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Biological reference points (BRPs) used in fisheries management do not include density‐dependent (DD) growth, with DD processes only considered in the stock recruitment relationship. Not accounting for DD on somatic growth has led to criticism that such BRPs underestimate the compensatory effects of DD at low stock size, and therefore risk foregone catch opportunities. Here, we analyse 81 stocks from the Northeast Atlantic for evidence of DD growth, defined as the process in which stock size affects somatic weight. We evaluate the following questions: (1) How many stocks have experienced instantaneous DD growth and do stocks of the same species display similar trends? (2) Is there a common instantaneous DD growth relationship shared by all stocks? (3) For stocks exhibiting significant instantaneous DD growth, can we quantify the strength of the relationship? (4) Is DD growth operating as an intra‐cohort process as opposed to an instantaneous effect? Results reveal that only the weight of recruits exhibits a common instantaneous DD growth while the other responses analysed show a positive, noncompensatory effect, suggesting that other processes are at work. All responses examined showed significant temporal autocorrelation, which, when not accounted for, suggest apparent instantaneous DD growth in several stocks. Comparison of instantaneous against intracohort DD growth showed an increase in the number of stocks with significant DD growth, although, as for instantaneous DD growth, this declined greatly when temporal autocorrelation was accounted for. Our results counteract the a priori assumption that DD growth compensation is related only to stock biomass or density, suggesting that DD growth should be dealt case‐by‐case. Consequently, management practices that aim to fish down stock biomass with the anticipation of triggering DD growth will be associated with greater asymmetric risks than keeping biomass at levels where replacement yield does not rely on it. [ABSTRACT FROM AUTHOR]

Inbreeding depression is a key factor regulating the evolution of self-fertilization in plants. Despite predictions that inbreeding depression should evolve with selfing rates as deleterious alleles are increasingly exposed and removed by selection, evidence of purging the genetic load in wild populations is equivocal at best. This discordance could be explained, in part, if the load underlying inbreeding depression is subject to soft selection, i.e., the fitness of selfed individuals depends on the frequency and density of selfed vs. outcrossed individuals in the population. Somewhat counterintuitively, this means that populations with contrasting mutation load can have similar fitness. Soft selection against selfed individuals may be expected when there is inbreeding depression for competitive ability in density-regulated populations. We tested population-level predictions of inbreeding depression in competitive ability by creating a density series of potted plants consisting of either purely outcrossed, purely selfed, or mixed (50% outcrossed, 50% selfed) seed of the mixed-mating biennial Sabatia angularis (Gentianaceae) representing ecological neighborhoods. Focusing on the growth and survival of juveniles, we show that mean plant size is independent of neighborhood composition when resources are limiting, but greatest in outcrossed neighborhoods at low densities. Across a range of densities, this manifests as stronger densitydependence in outcrossed populations compared to selfed or mixed ones. We also found significantly greater size inequalities among individuals in mixed neighborhoods, even at high densities where mean juvenile size converged, a key signature of asymmetric competition between outcrossed and selfed individuals. Our work illustrates how soft selection could shelter the genetic load underlying inbreeding depression and its demographic consequences. [ABSTRACT FROM AUTHOR]

Group living has well-known costs and benefits. Large groups may experience greater competition for resources, while simultaneously benefit from reduced risk through predator dilution. When there is a tradeoff between forage acquisition and predation risk, the ability to congregate into large groups may unlock access to previously unavailable habitat with high risk of predation, thereby increasing forage available to the population. We evaluated whether forage availability increased with population size and how it was mediated through changes in group size. There was a tradeoff between forage availability and predation risk. Larger groups used areas with more forage biomass and greater predation risk than smaller groups. Group size also increased with population abundance, meaning bighorn sheep used gentler terrain and areas with more forage biomass at greater population abundance. Group size functionally increased carrying capacity by yielding access to more resources for growing populations of gregarious ungulates. [ABSTRACT FROM AUTHOR]

Bivalves are becoming an increasingly popular tool to counteract eutrophication, particularly in vegetated coastal ecosystems where synergistic interactions between bivalves and plants can govern important N sequestration pathways. In turn, new calls to evaluate how bivalve densities modify N pools and processes across multiple scales have surfaced.Ribbed mussels, Geukensia demissa, and their relationship with smooth cordgrass present a classic demonstration of positive bivalve‐plant interactions and offer a useful model for assessing density dependence. We measure porewater ammonium concentrations, N stable isotope signatures in cordgrass tissue, and sediment N fluxes in mussel aggregations and in cordgrass‐only plots across a southeastern U.S. salt marsh.In addition to measuring the effect of mussel presence, we evaluate mussel density dependence through a multiscale approach. At the patch scale, we quantify mussel density effects within their aggregations (individuals m−2) while at a larger landscape scale, we quantify mussel density effects on the cordgrass‐only areas they neighbour (individuals ~30 m−2).Porewater ammonium concentrations were halved in mussel biodeposits relative to sediments in cordgrass‐only areas and negatively related to mussel density within aggregations. Leaf clip ẟ15N signatures were nearly 2‰ higher in cordgrass growing among mussel aggregations and increased with increasing patch mussel density. Microcosm incubations showed that mussels enhanced N2 flux (i.e., nitrogen removal) and DIN flux (i.e., N regeneration) into the water column, where only nitrogen removal increased with increasing patch‐scale mussel density. Across the marsh landscape, mussel coverage drove ammonium accumulation and N2 flux in sediments.Synthesis. Our results suggest that, at the patch scale, mussels stimulate the microbial metabolism of N, the assimilation of this bioavailable N by cordgrass, and nitrogen removal in a positive, density‐dependent manner. Tidal currents redistribute mussel biodeposits from mussel aggregations to surrounding areas, influencing biogeochemical transformations at scales beyond their physical footprint. We emphasize that the N regeneration potential of bivalve populations is a significant metric contributing to their mitigation potential and that bivalve density effects may be non‐linear, vary across patch to ecosystem scales, and have differing implications for the plants with which they interact. [ABSTRACT FROM AUTHOR]

Competition for resources and space can drive forage selection of large herbivores from the bite through the landscape scale. Animal behaviour and foraging patterns are also influenced by abiotic and biotic factors.Fine‐scale mechanisms of density‐dependent foraging at the bite scale are likely consistent with density‐dependent behavioural patterns observed at broader scales, but few studies have directly tested this assertion.Here, we tested if space use intensity, a proxy of spatiotemporal density, affects foraging mechanisms at fine spatial scales similarly to density‐dependent effects observed at broader scales in caribou. We specifically assessed how behavioural choices are affected by space use intensity and environmental processes using behavioural state and forage selection data from caribou (Rangifer tarandus granti) observed from GPS video‐camera collars using a multivariate discrete‐choice modelling framework.We found that the probability of eating shrubs increased with increasing caribou space use intensity and cover of Salix spp. shrubs, whereas the probability of eating lichen decreased. Insects also affected fine‐scale foraging behaviour by reducing the overall probability of eating. Strong eastward winds mitigated negative effects of insects and resulted in higher probabilities of eating lichen. At last, caribou exhibited foraging functional responses wherein their probability of selecting each food type increased as the availability (% cover) of that food increased.Space use intensity signals of fine‐scale foraging were consistent with density‐dependent responses observed at larger scales and with recent evidence suggesting declining reproductive rates in the same caribou population. Our results highlight potential risks of overgrazing on sensitive forage species such as lichen. Remote investigation of the functional responses of foraging behaviours provides exciting future applications where spatial models can identify high‐quality habitats for conservation. [ABSTRACT FROM AUTHOR]

Management of wildlife populations is most effective with a thorough understanding of the interplay among vital rates, population growth, and density-dependent feedback; however, measuring all relevant vital rates and assessing density-dependence can prove challenging. Integrated population models have been proposed as a method to address these issues, as they allow for direct modeling of density-dependent pathways and inference on parameters without direct data. We developed integrated population models from a 25-year demography dataset of Northern Bobwhites (Colinus virginianus) from southern Georgia, USA, to assess the demographic drivers of population growth rates and to estimate the strength of multiple density-dependent processes simultaneously. Furthermore, we utilize a novel approach combining breeding productivity and post-breeding abundance and age-and-sex ratio data to infer juvenile survival. Population abundance was relatively stable for the first 14 years of the study but began growing after 2012, showing that bobwhite populations may be stable or exhibit positive population growth in areas of intensive management. Variation in breeding and non-breeding survival drove changes in population growth in a few years; however, population growth rates were most affected by productivity across the entire study duration. A similar pattern was observed for density-dependence, with relatively stronger negative effects of density on productivity than on survival. Our novel modeling approach required an informative prior but was successful at updating the prior distribution for juvenile survival. Our results show that integrated population models provide an attractive and flexible method for directly modeling all relevant density-dependent processes and for combining breeding and post-breeding data to estimate juvenile survival in the absence of direct data.

ABSTRACT Biological reference points (BRPs) used in fisheries management do not include density‐dependent (DD) growth, with DD processes only considered in the stock recruitment relationship. Not accounting for DD on somatic growth has led to criticism that such BRPs underestimate the compensatory effects of DD at low stock size, and therefore risk foregone catch opportunities. Here, we analyse 81 stocks from the Northeast Atlantic for evidence of DD growth, defined as the process in which stock size affects somatic weight. We evaluate the following questions: (1) How many stocks have experienced instantaneous DD growth and do stocks of the same species display similar trends? (2) Is there a common instantaneous DD growth relationship shared by all stocks? (3) For stocks exhibiting significant instantaneous DD growth, can we quantify the strength of the relationship? (4) Is DD growth operating as an intra‐cohort process as opposed to an instantaneous effect? Results reveal that only the weight of recruits exhibits a common instantaneous DD growth while the other responses analysed show a positive, noncompensatory effect, suggesting that other processes are at work. All responses examined showed significant temporal autocorrelation, which, when not accounted for, suggest apparent instantaneous DD growth in several stocks. Comparison of instantaneous against intracohort DD growth showed an increase in the number of stocks with significant DD growth, although, as for instantaneous DD growth, this declined greatly when temporal autocorrelation was accounted for. Our results counteract the a priori assumption that DD growth compensation is related only to stock biomass or density, suggesting that DD growth should be dealt case‐by‐case. Consequently, management practices that aim to fish down stock biomass with the anticipation of triggering DD growth will be associated with greater asymmetric risks than keeping biomass at levels where replacement yield does not rely on it.

Intraspecific competition and resource diversity are considered major drivers of niche differentiation, which are expected to promote population niche expansion by driving individuals to feed on alternative resources and/or by enhancing individual diet specialization. Nevertheless, experimental studies on the interaction effects of both factors on animal behavior and population dynamics remain scant. Here, we investigate how resource diversity alters the impact of intraspecific competition on resource preference and fitness of three co-occurring cryptic species of the marine nematode complex Litoditismarina (PmI,PmIII andPmIV). Foreachcryptic species, two competition regimes ('low nematode density' and 'high nematode density') were established in microcosms with varying resource diversity (E. coli, low-, mediumand high-diversity food). Our results show differences in resource preference and population fitness depending on intraspecific competition and resource diversity, but the response also varied considerably between cryptic species. Pm III did not exhibit resource preference under low intraspecific competition, but preferred the two most diverse food sources under high intraspecific competition. Pm IV also showed preference for medium-diversity food under high competition, whereas no resource preference was observed in Pm I regardless of competition regimes and resource diversity. Nevertheless, all cryptic species exhibited enhanced adult population growth on a more diverse food source under stronger intraspecific competition. These results indicate that resource diversity can alleviate intraspecific competition and affect niche diversification, which may impact diversity maintenance in ecological communities. [ABSTRACT FROM AUTHOR]

Inbreeding depression is a key factor regulating the evolution of self-fertilization in plants. Despite predictions that inbreeding depression should evolve with selfing rates as deleterious alleles are increasingly exposed and removed by selection, evidence of purging the genetic load in wild populations is equivocal at best. This discordance could be explained, in part, if the load underlying inbreeding depression is subject to soft selection, i.e., the fitness of selfed individuals depends on the frequency and density of selfed vs. outcrossed individuals in the population. Somewhat counterintuitively, this means that populations with contrasting mutation load can have similar fitness. Soft selection against selfed individuals may be expected when there is inbreeding depression for competitive ability in density-regulated populations. We tested population-level predictions of inbreeding depression in competitive ability by creating a density series of potted plants consisting of either purely outcrossed, purely selfed, or mixed (50% outcrossed, 50% selfed) seed of the mixed-mating biennial Sabatia angularis (Gentianaceae) representing ecological neighborhoods. Focusing on the growth and survival of juveniles, we show that mean plant size is independent of neighborhood composition when resources are limiting, but greatest in outcrossed neighborhoods at low densities. Across a range of densities, this manifests as stronger density-dependence in outcrossed populations compared to selfed or mixed ones. We also found significantly greater size inequalities among individuals in mixed neighborhoods, even at high densities where mean juvenile size converged, a key signature of asymmetric competition between outcrossed and selfed individuals. Our work illustrates how soft selection could shelter the genetic load underlying inbreeding depression and its demographic consequences.

Group living has well-known costs and benefits. Large groups may experience greater competition for resources, while simultaneously benefit from reduced risk through predator dilution. When there is a tradeoff between forage acquisition and predation risk, the ability to congregate into large groups may unlock access to previously unavailable habitat with high risk of predation, thereby increasing forage available to the population. We evaluated whether forage availability increased with population size and how it was mediated through changes in group size. There was a tradeoff between forage availability and predation risk. Larger groups used areas with more forage biomass and greater predation risk than smaller groups. Group size also increased with population abundance, meaning bighorn sheep used gentler terrain and areas with more forage biomass at greater population abundance. Group size functionally increased carrying capacity by yielding access to more resources for growing populations of gregarious ungulates.

Body size is a key component of individual fitness and an important factor in the structure and functioning of populations and ecosystems. Disentangling the effects of environmental change, harvest and intra‐ and inter‐specific trophic effects on body size remains challenging for populations in the wild. Herring in the Northwest Atlantic provide a strong basis for evaluating hypotheses related to these drivers given that they have experienced significant warming and harvest over the past century, while also having been exposed to a wide range of other selective constraints across their range. Using data on mean length‐at‐age 4 for the sixteen principal populations over a period of 53 cohorts (1962–2014), we fitted a series of empirical models for temporal and between‐population variation in the response to changes in sea surface temperature. We find evidence for a unified cross‐population response in the form of a parabolic function according to which populations in naturally warmer environments have responded more negatively to increasing temperature compared with those in colder locations. Temporal variation in residuals from this function was highly coherent among populations, further suggesting a common response to a large‐scale environmental driver. The synchrony observed in this study system, despite strong differences in harvest and ecological histories among populations and over time, clearly indicates a dominant role of environmental change on size‐at‐age in wild populations, in contrast to commonly reported effects of fishing. This finding has important implications for the management of fisheries as it indicates that a key trait associated with population productivity may be under considerably less short‐term management control than currently assumed. Our study, overall, illustrates the need for a comparative approach within species for inferences concerning the many possible effects on body size of natural and anthropogenic drivers in the wild. [ABSTRACT FROM AUTHOR]

The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), pupates in the soil, and the average pupation depth increases with the number of concurrently pupating individuals at the same location. This study aimed to explain the density‐dependent pupation depth in B. dorsalis. Previous studies demonstrated that increasing pupation depth has the benefit of reduced parasitism and predation risk and the cost of reduced emergence success (i.e., eclosed adults in the soil fail to reach above ground). It was hypothesized that density‐dependent pupation depth is governed by density‐dependent cost. That is, emergence success of eclosed adults increases with density because the soil is more easily loosened as the number of individuals increases. Pupating larvae can reduce parasitism and predation risk by increasing pupation depth, but only those in high density can afford to pupate at deep depths due to the associated cost. To test the hypothesis, density‐dependent emergence success in B. dorsalis was examined in the laboratory. Newly pupated individuals were buried in peat moss approximately 5 cm below the surface, and the relationship between the number of buried pupae (four levels: 1, 25, 50, and 100 pupae) and their emergence success was recorded. To manipulate the difficulty of emergence, the level of peat moss compaction was also varied. Emergence success was uniformly high when peat moss was not heavily compacted regardless of the number of pupae, but the number of pupae had a positive effect on emergence success when the peat moss was heavily compacted. In addition, the timing of emergence was more synchronized in the highest density than in the lower densities. The results of this study, in combination with the previous findings, support the hypothesis. [ABSTRACT FROM AUTHOR]

Premise: Density‐dependent pollinator visitation can lead to density‐dependent mating patterns and within‐population genetic structure. In Gymnadenia conopsea, individuals in low‐density patches receive more self pollen than individuals in high‐density patches, suggesting higher relatedness at low density. Ongoing fragmentation is also expected to cause more local matings, potentially leading to biparental inbreeding depression. Methods: To evaluate whether relatedness decreases with local density, we analyzed 1315 SNP loci in 113 individuals within two large populations. We quantified within‐population genetic structure in one of the populations, recorded potential habitat barriers, and visualized gene flow using estimated effective migration surfaces (EEMS). We further estimated the magnitude of biparental inbreeding depression that would result from matings restricted to within 5 m. Results: There was no significant relationship between local density and relatedness in any population. We detected significant fine‐scale genetic structure consistent with isolation by distance, with positive kinship coefficients at distances below 10 m. Kinship coefficients were low, and predicted biparental inbreeding depression resulting from matings within the closest 5 m was a modest 1–3%. The EEMS suggested that rocks and bushes may act as barriers to gene flow within a population. Conclusions: The results suggest that increased self‐pollen deposition in sparse patches does not necessarily cause higher selfing rates or that inbreeding depression results in low establishment success of inbred individuals. The modest relatedness suggests that biparental inbreeding depression is unlikely to be an immediate problem following fragmentation of large populations. The results further indicate that habitat structure may contribute to governing fine‐scale genetic structure in G. conopsea. [ABSTRACT FROM AUTHOR]

Keystone plant species are commonly used for restoring degraded terrestrial sites because, despite being encountered in low abundances in natural communities, they interact with multiple species across multiple niche dimensions. Nevertheless, the demographic characteristics of these "great interactors" are often disregarded in restoration planning, which may bring unintended consequences for restoration trajectories once the outcome of species relationships interplays between positive and negative effects depending on the density of interacting species. Therefore, while replanting keystone species at their characteristically low densities may re‐entangle food webs and allow novel plant and animal recruitment, restoring them at high densities can assemble asymmetrical relationships strong enough to affect sympatric plant species establishment, survival, and reproduction. Here, we explore the negative consequences of overusing keystone plant species in sites undergoing restoration and provide specific guidelines for practitioners to maximize the benefits of keystone plants in restoration initiatives. [ABSTRACT FROM AUTHOR]

Abstract Regular assessment of reintroduced populations is essential to guide management and provide lessons for other reintroduction projects. Bearded vulture Gypaetus barbatus reintroduction in the Alps began in 1986 with the release of the first fledglings, the first successful reproduction was recorded in 1997, and the population has grown steadily since. A previous assessment suggested that no further releases would be required to establish a self‐sustaining population from a demographic point of view. However, this conclusion was based on a small sample size and spatially homogeneous demographic rates of released individuals, which may differ from and be spatially variable among wild‐hatched individuals. Using longitudinal data and breeding site survey data, we constructed an integrated population model to examine the demography of the entire Alpine population, spatially stratified into a core and a periphery. We performed retrospective population analyses to identify demographic reasons for spatial differences in population growth and conducted population viability analyses to assess the impact of future threats and reintroduction options. In 2021, an estimated 172 (CRI: 147–198) females were present in the Alps, of which 65 (CRI: 63–67) were breeders. Adult survival and productivity were higher in the core than in the periphery, so the population grew more strongly in the core than in the periphery. Differences in adult survival contributed most to the differences in population growth between the two areas. The population viability analysis predicts that the Alpine population will double in 10 years but that an increase in the mortality hazard above 0.055 will lead to a population decline. Unlike the population in the core, the population in the periphery is dependent on further releases at this stage. Bearded vulture reintroductions in the Alps have succeeded in creating a self‐sustaining population with higher reproductive success and similar survival probabilities to the autochthonous Pyrenean population. In general, management should focus on preventing further mortality risks. In the periphery, reducing current mortality and increasing reproductive success are essential to make the population independent of releases.

Intraspecific competition and resource diversity are considered major drivers of niche differentiation, which are expected to promote population niche expansion by driving individuals to feed on alternative resources and/or by enhancing individual diet specialization. Nevertheless, experimental studies on the interaction effects of both factors on animal behavior and population dynamics remain scant. Here, we investigate how resource diversity alters the impact of intraspecific competition on resource preference and fitness of three co-occurring cryptic species of the marine nematode complex Litoditis marina (Pm I, Pm III and Pm IV). For each cryptic species, two competition regimes (‘low nematode density’ and ‘high nematode density’) were established in microcosms with varying resource diversity (E. coli, low-, medium- and high-diversity food). Our results show differences in resource preference and population fitness depending on intraspecific competition and resource diversity, but the response also varied considerably between cryptic species. Pm III did not exhibit resource preference under low intraspecific competition, but preferred the two most diverse food sources under high intraspecific competition. Pm IV also showed preference for medium-diversity food under high competition, whereas no resource preference was observed in Pm I regardless of competition regimes and resource diversity. Nevertheless, all cryptic species exhibited enhanced adult population growth on a more diverse food source under stronger intraspecific competition. These results indicate that resource diversity can alleviate intraspecific competition and affect niche diversification, which may impact diversity maintenance in ecological communities.

Identifying factors affecting the survival of individuals is essential for understanding the evolution of life-history traits and population dynamics. Despite numerous studies on this subject in north-temperate environments, there is a lack of equivalent studies at similar latitudes in the south. Here, we used a 14-year dataset of capture, banding, and resighting to estimate the annual variation in the apparent adult survival probability of a south-temperate population of House Wrens (Troglodytes aedon bonariae). We evaluated temporal variation in survival and the effect of environmental (climatic) and demographic variables (adult abundance, total number of fledglings produced during each breeding season) on survival estimators. We found that the probability of adult survival decreased as the abundance of breeding adults increased. This density-dependent effect could be related to the resident lifestyle of southern House Wrens, which could determine an intense competition for territories and resources that ultimately would affect their survival.

Conspecific plant density and heterospecific frequency are key drivers of herbivore damage. However, most studies have investigated their effects separately and for single (rather than multiple) focal plant species.We conducted an experiment involving three tree species, namely: Cordia dodecandra (Boraginaceae), Manilkara zapota (Zapotaceae), and Piscidia piscipula (Fabaceae). We manipulated understory densities of M. zapota and C. dodecandra (focal species) and their frequency relative to P. piscipula. Three months after planting, we surveyed insect leaf chewer and sucking damage on the former two. Because these species are attacked by different herbivores, we predicted a negative effect of heterospecific frequency on herbivory.Density and frequency varied in the direction and function of their effects on herbivory depending on the plant species and attacking herbivore. As expected, Piscidia piscipula frequency had a negative linear effect on M. zapota leaf‐chewer damage, whereas conspecific density did not affect chewer damage on this species. In contrast, density and frequency had non‐linear effects on C. dodecandra chewer damage, namely positive (hump‐shaped) and negative (U‐shaped) relationships, respectively. In addition, density and frequency had positive linear effects on C. dondecandra damage by leafhoppers.These findings call for more work jointly assessing plant inter‐specific variation in density‐ and frequency‐dependent variation in herbivory and its underlying drivers. [ABSTRACT FROM AUTHOR]

The Janzen–Connell hypothesis (JCH) predicts that attack by specialist enemies on seedlings increases with conspecific seedling density, but studies have rarely experimentally tested for the contingency of such effects on the tree community context (e.g. diversity, composition) ormeasured responses by different enemies (e.g. herbivores, pathogens). We conducted a field study in a large‐scale system evaluating tree species diversity and conspecific density effects on leaf damage on mahogany Swietenia macrophylla seedlings. We established quadrats of eight levels of seedling density across mahogany tree monocultures and tree species polycultures including mahogany, and recorded percent leaf damage by insects and percent leaf necrosis by a pathogenic fungus on mahogany seedlings. We found contrasting effects of tree species diversity on insects and pathogens. Whereas tree diversity did not affect leaf damage by insects, it had a significant negative effect on leaf necrosis by pathogens whereby, on average, percent leaf necrosis on mahogany seedlings in polyculture was half of that observed in monoculture. We discuss the potential influences of changes in mahogany tree density versus frequency (relative to other tree species) driving this diversity effect. Unexpectedly, we found no effect of seedling conspecific density on either leaf insect or pathogen damage (i.e. density‐independent attack). Likewise, we found no significant tree diversity by seedling density interaction, indicating that plant enemies were consistently unresponsive to variation in seedling density acrosslevels of tree diversity. Overall, this study provides a unique test of the JCH by experimentally evaluating seedling density and tree diversity effects on contrasting plant enemies and, in turn, the controls they exert over plant recruitment. [ABSTRACT FROM AUTHOR]

Inferring the strength of species interactions from demographic data is a challenging task. The Integrated Population Modelling (IPM) approach, bringing together population counts, capture-recapture, and individual-level fecundity data into a unified model framework, has been extended from single species to the community level. This allows to specify IPMs for multiple species with interactions specified as links between vital rates and stage-specific densities. However, there is no evaluation of such models when interactions are actually absent---while any interaction inference method runs the risk of producing false positives. We investigate here whether multispecies IPMs could output interactions where there are in fact none, building on an existing predator-prey IPM. We show that interspecific density-dependence estimates are centered on zero when simulated to be zero, and therefore their estimation is unbiased. Their coverage probability, quantifying how many times credible intervals include zero, is also satisfactory. We further confirm that adding random temporal variation to multispecies density-dependent link functions does not alter these results. This study therefore reaffirms the potential of multispecies IPMs to infer correctly how biotic interactions influence demography, although future studies should investigate model misspecifications.

Cannibalism (i.e., intraspecific predation) affects the population dynamics of many invertebrate species. Cannibalism by the predatory cladoceran Bythotrephes cederströmii Schödler, 1863 has been observed and noted in laboratory settings on several occasions, but no studies have published results of cannibalism experiments or explicitly quantified Bythotrephes cannibalism rates. We performed two laboratory experiments that demonstrated and quantified Bythotrephes cannibalism. Cannibalism occurred frequently in our experiments, and cannibalism clearance rates were comparable to those for Bythotrephes feeding on heterospecific prey. Further, our estimates of clearance rates between conspecifics suggest that cannibalism could be an important food source during certain periods of the year, and in particular places, for which Bythotrephes densities are at the higher end of observed ranges. While more research is needed, our results suggest that there are conditions in which cannibalism should be included in models of Bythotrephes predation, including bioenergetics models predicting Bythotrephes consumption rates. [ABSTRACT FROM AUTHOR]

In this report I examine tradeoffs involving body size, age, and resource allocation within the framework of the Equal Fitness Paradigm (EFP) in six species of plethodontid salamanders of the genus Desmognathus in two assemblages in the southern Blue Ridge Mountains of North Carolina. The species are representative of the three life-history modes associated with habitat utilization in Desmognathus, namely stream, streamside, and forest. The two assemblages include the largest and smallest members of the genus. Among species, I recorded a negative correlation between body size and relative offspring size, a positive correlation between body size and lifetime offspring number, but negative correlations between body size and both lifetime reproductive investment and productivity, as reflected in the decrease in body size with increasing relative offspring size. In comparing these trends with published data on variation in these parameters in animals generally, I conclude that desmognathan salamanders lie at the slow end of the fast–slow axis in the pace-of-life model of life-history evolution. I discuss possible population regulatory mechanisms that operate on these populations, as a function of life-history mode, with special emphasis on streamside species. I suggest that retention of a brief larval phase in streamside species reflects tradeoffs among dispersal-related traits, including survival and growth. [ABSTRACT FROM AUTHOR]

Endangered species, despite often living at low population densities, may undergo unexpected density‐dependent feedbacks in the case of successful recovery or marked reduction in range. Because density‐dependence dynamics can increase risk of extinction, these effects can hamper conservation efforts. In this study, we analyze the dynamics of the largest population of the tamaraw Bubalus mindorensis, a critically endangered ungulate species endemic to Mindoro island, Philippines. The population is located within a <3000 ha area in Mounts Iglit‐Baco Natural Park, with limited expansion possibilities. We took advantage of a 22 year time series of tamaraw counts to estimate annual population growth rate and possible density‐dependence, accounting for sampling errors in the counts. The tamaraw population has been increasing at an average rate of +5% per year, as would be expected given its protected status by law. Population growth showed strong spatial structuring, with a population growth close to +10% in the core area of protection, and a reduction of abundance of −5% at the periphery of its range, inside the protected area. This range constriction is concerning because our best population dynamics model suggests significant negative density‐dependence (Bayes factor = 0.9). The contraction of tamaraw range is likely caused by anthropogenic pressures forcing the species to live at relatively high densities in the core zone where protection is most effective, creating source‐sink dynamics. Our study highlights the fact that, despite the continuous population growth over the last two decades, the long‐term viability of the Mounts Iglit‐Baco Natural Park tamaraw population remains uncertain. [ABSTRACT FROM AUTHOR]

Many of the world's native fauna suffer unsustainable losses from invasive mammalian predators. Conservation managers control predators on the premise that if large numbers are removed, prey will respond. This is sometimes true, but not always. Empirical relationships between predator densities and responses of vulnerable prey in Oceania often show little or no response across a broad range of predator reductions, with positive responses only at low threshold predator densities. Even then, some prey populations fail to respond. More research is required to identify predator thresholds across a range of prey taxa. This uncertainty of outcomes, coupled with the considerable cost of mammalian pest control, risks little or no return from limited conservation funds. A unifying theory is required to help understand why conservation outcomes from predator control are so variable despite the best efforts of conservation managers, and to expedite the right kind of management for a given prey species. We argue that a modern synthesis of numerical and functional response theory, in the form of total response models, provides such a theory. Stochastic consumer‐resource models are recommended for dynamic systems, but they are difficult to parameterize. Total response models, on the other hand, present a simple conceptual framework that managers can use as a heuristic to understand predator–prey systems, help explain some of the variability in predator control outcomes and stimulate thinking about other management options that can be integrated with predator control to improve conservation outcomes. Five rules of thumb are suggested to assist conservation managers. [ABSTRACT FROM AUTHOR]

Characterizing dispersal kernels from truncated data is important for managing and predicting population dynamics. We used mark‐recapture data from 10 previously published replicated experiments at three host plant development stages (seedling, tillering, and heading) to estimate parameters of the normal and exponential dispersal kernels for green rice leafhopper, Nephotettix cincticeps (Uhler). We compared classic statistical methods for estimating untruncated distribution parameters from truncated data with maximum likelihood (MLE) and the method of statistical moments for simulated and empirical data. Simulations showed that both methods provided accurate parameter estimates with similar precision. The method of moments is algebraically complex, but simple to calculate, while the MLE methods require numerical solutions of nonlinear equations. Simulations also showed that accurate, precise estimates of the parameters of the untruncated distributions could be attained even under severe truncation with sufficient numbers of recaptures. Both diffusivity and the exponential mean were higher with later plant growth stage, showing that insects moved farther and faster at the heading stage. Precision of the estimates was not strongly related to percent capture, size of the experimental field, or the number of leafhoppers captured. The leptokurtic exponential kernel fit the data better than the normal kernel for all the experiments. These results support an alternative explanation for the strong density‐dependent population regulation of this species at the heading stage. Instead of leafhopper density per se, the increase in movement at this stage could integrate the populations in the separate fields, leveling densities throughout the landscape. [ABSTRACT FROM AUTHOR]

Abstract Many of the world's native fauna suffer unsustainable losses from invasive mammalian predators. Conservation managers control predators on the premise that if large numbers are removed, prey will respond. This is sometimes true, but not always. Empirical relationships between predator densities and responses of vulnerable prey in Oceania often show little or no response across a broad range of predator reductions, with positive responses only at low threshold predator densities. Even then, some prey populations fail to respond. More research is required to identify predator thresholds across a range of prey taxa. This uncertainty of outcomes, coupled with the considerable cost of mammalian pest control, risks little or no return from limited conservation funds. A unifying theory is required to help understand why conservation outcomes from predator control are so variable despite the best efforts of conservation managers, and to expedite the right kind of management for a given prey species. We argue that a modern synthesis of numerical and functional response theory, in the form of total response models, provides such a theory. Stochastic consumer‐resource models are recommended for dynamic systems, but they are difficult to parameterize. Total response models, on the other hand, present a simple conceptual framework that managers can use as a heuristic to understand predator–prey systems, help explain some of the variability in predator control outcomes and stimulate thinking about other management options that can be integrated with predator control to improve conservation outcomes. Five rules of thumb are suggested to assist conservation managers.

Plants are attacked by multiple herbivores, and depend on a precise regulation of responses to cope with a wide range of antagonists. Simultaneous herbivory can occur in different plant compartments, which may pose a serious threat to plant growth and reproduction. In particular, plants often face co-occurring root and floral herbivory, but few studies have focused on such interactions. Here, we investigated in the field the combined density-dependent effects of root-chewing cebrionid beetle larvae and flower-chewing pierid caterpillars on the fitness and defense of a semiarid Brassicaceae herb. We found that the fitness impact of both herbivore groups was independent and density-dependent. Increasing root herbivore density non-significantly reduced plant fitness, while the relationship between increasing floral herbivore density and the reduction they caused in both seed number and seedling emergence was non-linear. The plant defensive response was non-additive with regard to the different densities of root and floral herbivores; high floral herbivore density provoked compensatory investment in reproduction, and this tolerance response was combined with aboveground chemical defense induction when also root herbivore density was high. Plants may thus prioritize specific trait combinations in response to varying combined below- and aboveground herbivore densities to minimize negative impacts on fitness. [ABSTRACT FROM AUTHOR]

Fishing gear-based landings or survey methods are often used to make assessments of species stock abundance. In order to convert catch into abundance values, estimates or assumptions are made on the catch efficiency of the gear-based method. This is the case in areas where flat oysters, Ostrea edulis, are surveyed for fisheries and conservation objectives in a range of projects across Europe. Flat oyster dredge efficiency assumptions vary widely from 5–30% in published studies and uncertainty in what is an appropriate efficiency estimate has led some survey teams to switch to Catch-per-unit-effort (CPUE), where CPUE is also of concern should catch efficiency change with shellfish density, ground type or some other unmeasured variable such as shellfish distribution. We undertook an experimental approach to estimate dredge efficiency in a standard ladder dredge used to harvest and survey adult flat oysters in the UK and Ireland. The dredge efficiency trials assessed how efficiency was influenced by oyster density (between 1 and 2.2 oysters m2), distribution (clumped vs uniform) and ground types across a gradient of more hard to more soft surface sediments. Dredge efficiency was significantly affected by oyster distribution, but also density and ground hardness as well as their interactions. While a median value between 7 and 10% seems an appropriate universal ladder dredge efficiency to adopt, ground type and distribution had such an effect that local conditions may effect this considerably. Catch efficiency was negatively density-dependent, this makes CPUE methods challenging where oyster densities are likely to vary. Practitioners, regulators and researchers conducting surveys can improve CPUE approaches through standard techniques and knowledge of how catch efficiency varies as we have presented here. [ABSTRACT FROM AUTHOR]

Mast seeding, a phenomenon observed in numerous perennial plant species, is highly variable reproduction across years, synchronized among individuals within a population. One major fitness advantage of masting is the reduced seed predation rates, achieved through alternating seed scarcity and abundance that starve and subsequently satiate seed consumers. Proximately, the variability in seed production frequently correlates with weather conditions. Convergent responses among species to weather fluctuations often lead to synchronized masting events across species, which may help with predator satiation, but this hypothesis has rarely been tested. Here, we address this gap by using 23 years of seed production and pre-dispersal seed predation monitoring in three North American oak species (Quercus rubra , Quercus alba , Quercus montana). We found that spring and summer weather patterns correlated with masting events in all three species, resulting in intraspecific synchrony levels ranging from 0.21 to 0.38, depending on the species pair. Intraspecific masting synchrony facilitated efficient insect starvation in Q. rubra and Q. alba , while community-wide mast years were necessary for satiation in Q. montana. Our findings present a rare empirical test supporting the hypothesis that intraspecific masting synchrony enhances reproductive efficiency by minimizing seed losses to generalist pre-dispersal seed predators. Improved seed survival via community-wide masting implies that stands with diverse oak species may have improved regeneration potential, suggesting management options for increased seed supply. • Mast seeding is variable reproduction over years, synchronized in populations. • Masting reduces seed predation by alternating seed scarcity and abundance. • Weather impacts seed production, synchronizing masting events across species. • A 23-year study shows intraspecific masting synchrony aids predator satiation. • Stands with diverse oak species may have improved regeneration potential [ABSTRACT FROM AUTHOR]

Understanding the interacting role of climate and habitat in shaping wildlife population dynamics can help to reveal synergistic pathways that drive population resilience or decline across variable and changing environments. Moose (Alces alces) is a pan-boreal herbivore experiencing population declines across large portions of North America; however, the species has shown variable response to climate across its distribution. We investigated moose demographic response to climate and evaluated the interacting role of habitat across 36 years and along a biogeographic gradient in Ontario, Canada that has experienced decadal changes to climate and habitat quality. Moose density exhibited a nonlinear trend that initially increased and then decreased over the study timeframe and was negatively affected by regional and local patterns of winter severity and later frost onset. Recruitment exhibited a monotonic decline and was positively affected by spring heat and deciduous forest cover, while also exhibiting density-dependent effects. The negative response of moose density to winter severity was reduced in Wildlife Management Units (WMUs) with higher proportions of dense canopy cover, supporting expectations that this habitat type improves moose winter mobility and predator avoidance. The negative effect of later frost onset was greater in WMUs with more regenerating forest, and both variables are associated with higher exposure to parasites and predators. Further, density-dependent effects on recruitment were suppressed by warmer springs that support vegetation productivity and in WMUs with higher proportions of dense canopy cover that can provide concealment from predators. Our study illustrates the important role habitat conditions can have to mitigate, or exacerbate, climate-change effects for a wide-spread herbivore occupying variable environments by potentially altering pathways relevant to energetic balance, predation, and parasite transmission. In this system, moose occupying sparse or regenerating forests are more susceptible to adverse climatic effects and should be managed accordingly.

The consequences of fisheries-induced evolution on stock productivity and yield depend, to a large extent, on the general prospects for growth and survival. Here, we compare the selection pressures imposed by two distinct patterns of exploitation—principally targeting spawning or non-spawning aggregations—on age at maturity among 15 Canadian stocks of Atlantic herring (Clupea harengus) that have exhibited a consistent pattern of length-at-age responses to common large-scale environmental drivers since the 1960s. In accordance with expectations for maturity-dependent harvesting, the establishment of a spawner-targeted fishery in the southern Gulf of St. Lawrence coincided with a shift towards delayed maturity in both resident stocks, whereas stocks elsewhere subject to fisheries that also exploited juveniles more commonly exhibited trends towards earlier maturity. Despite these differences, we find that environmentally driven changes in length at maturation, combined with total mortality, may overwhelmingly determine lifetime reproductive success and possibly fitness. By linking phenotypic changes experienced in the juvenile period to simple correlates of egg production in mature age classes, our study highlights the importance of managing fisheries in the context of ubiquitous but contrasting environmental constraints on life histories. [ABSTRACT FROM AUTHOR]

We study an interspecific, density-dependent model of two species competing for a single nutrient in a chemostat, allowing for a predator-prey relationship between them. We have previously examined the system in the absence of species mortality, showing that multiple positive steady states can appear and disappear through a saddle-node or transcritical bifurcation. In this paper we include mortality. We give a complete analysis for the existence and local stability of all steady states of the three-dimensional system that cannot be reduced to two dimensional ones. Specializing the forms of the rate functions, we show how mortality destabilizes the positive steady state and that stable limit cycles emerge through supercritical Hopf bifurcations. To describe how the process behaves with respect to the choice of dilution rate and input concentration as control parameters, we determine the operating diagram theoretically and also numerically by using the software package MATCONT. The bifurcation diagram based on the input concentration shows various types of bifurcations of steady states, and coexistence either at a positive steady state or via sustained oscillations. [ABSTRACT FROM AUTHOR]

Hunting and fishing are often size-selective, which favours slow body growth. In addition, fast growth rate has been shown to be positively correlated with behavioural traits that increase encounter rates and catchability in passive fishing gears such as baited traps. This harvest-induced selection should be effectively eliminated in no-take marine-protected areas (MPAs) unless strong density dependence results in reduced growth rates. We compared body growth of European lobster (Homarus gammarus) between three MPAs and three fished areas. After 14 years of protection from intensive, size-selective lobster fisheries, the densities in MPAs have increased considerably, and we demonstrate that females moult more frequently and grow more during each moult in the MPAs. A similar, but weaker pattern was evident for males. This study suggests that MPAs can shield a wild population from slow-growth selection, which can explain the rapid recovery of size structure following implementation. If slow-growth selection is a widespread phenomenon in fisheries, the effectiveness of MPAs as a management tool can be higher than currently anticipated. [ABSTRACT FROM AUTHOR]

Harvest of wild organisms is an important component of human culture, economy, and recreation, but can also put species at risk of extinction. Decisions that guide successful management actions therefore rely on the ability of researchers to link changes in demographic processes to the anthropogenic actions or environmental changes that underlie variation in demographic parameters.Ecologists often use population models or maximum sustained yield curves to estimate the impacts of harvest on wildlife and fish populations. Applications of these models usually focus exclusively on the impact of harvest and often fail to consider adequately other potential, often collinear, mechanistic drivers of the observed relationships between harvest and demographic rates. In this study, we used an integrated population model and long‐term data (1973–2016) to examine the relationships among hunting and natural mortality, the number of hunters, habitat conditions, and population size of blue‐winged teal Spatula discors, an abundant North American dabbling duck with a relatively fast‐paced life history strategy.Over the last two and a half decades of the study, teal abundance tripled, hunting mortality probability increased slightly (<0.02), and natural mortality probability increased substantially (>0.1) at greater population densities. We demonstrate strong density‐dependent effects on natural mortality and fecundity as population density increased, indicative of compensatory harvest mortality and compensatory natality. Critically, an analysis that only assessed the relationship between survival and hunting mortality would spuriously indicate depensatory mortality due to multicollinearity between abundance, natural mortality and hunting mortality.Our findings demonstrate that models that only consider the direct effect of hunting on survival or natural mortality can fail to accurately assess the mechanistic impact of hunting on population dynamics due to multicollinearity among demographic drivers. This multicollinearity limits inference and may have strong impacts on applied management actions globally. [ABSTRACT FROM AUTHOR]

Dispersive movements are often thought to be multicausal and driven by individual body size, sex, conspecific density, environmental variation, personality, and/or other variables. Yet such variables often do not account for most of the variation among dispersive movements in nature, leaving open the possibility that dispersion may be indeterministic. We assessed the amount of variation in 24 h movement distances that could be accounted for by potential drivers of displacement with a large empirical dataset of movement distances performed by Fowler's Toads (Anaxyrus fowleri) on the northern shore of Lake Erie at Long Point, Ontario (2002–2021, incl.). These toads are easy to sample repeatedly, can be identified individually and move parallel to the shoreline as they forage at night, potentially dispersing to new refuge sites. Using a linear mixed‐effect model that incorporated random effect terms to account for sampling variance and inter‐annual variation, we found that all potential intrinsic and extrinsic drivers of movement accounted for virtually none of the variation observed among 24 h distances moved by these animals, whether over short or large spatial scales. We examined the idea of movement personality by testing variance per individual toad and found no evidence of individuality in movement distances. We conclude that deterministic variables, whether intrinsic or extrinsic, neither can be shown to nor are necessary to drive movements in this population over all spatial scales. Stochastic, short time‐scale movements, such as daily foraging movements, can instead accumulate over time to produce large spatial‐scale movements that are dispersive in nature. [ABSTRACT FROM AUTHOR]

The mechanisms determining habitat use in animal populations have important implications for population dynamics, conservation, and management. Here, we investigated how an increase in annual numbers of brown bear females with cubs of the year (FCOY) in a growing, yet threatened population, could explain differences in the habitat characteristics around reproductive dens. Habitat characteristics around FCOY dens were compared between a low bear density period (1995–2005) and a period when the population was increasing (2006–2016). We also compared the distance to the nearest breeding area and to all other breeding areas observed during the same year. The results suggested that during the second period, breeding areas were closer to rivers, fruit trees, and anthropogenic sources of disturbance (trails, highways) than in 1995–2005. There were also shorter distances to the closest neighboring breeding area, while the mean distance among FCOY breeding areas increased as the population grew and expanded at the landscape level. These changes may reflect that the best den locations were increasingly occupied (i.e., ideal-despotic distribution), and may be further explained by the avoidance of conspecifics by FCOY in a critical time of the year, when newborn cubs are most vulnerable. We suggest that both density-dependent factors and human-related features of the landscape are crucial to understanding long-term dynamics in the habitat use of a threatened species. [ABSTRACT FROM AUTHOR]

Management of wildlife populations is most effective with a thorough understanding of the interplay among vital rates, population growth, and density-dependent feedback; however, measuring all relevant vital rates and assessing density-dependence can prove challenging. Integrated population models have been proposed as a method to address these issues, as they allow for direct modeling of density-dependent pathways and inference on parameters without direct data. We developed integrated population models from a 25-year demography dataset of Northern Bobwhites ( Colinus virginianus ) from southern Georgia, USA, to assess the demographic drivers of population growth rates and to estimate the strength of multiple density-dependent processes simultaneously. Furthermore, we utilize a novel approach combining breeding productivity and post-breeding abundance and age-and-sex ratio data to infer juvenile survival. Population abundance was relatively stable for the first 14 years of the study but began growing after 2012, showing that bobwhite populations may be stable or exhibit positive population growth in areas of intensive management. Variation in breeding and non-breeding survival drove changes in population growth in a few years; however, population growth rates were most affected by productivity across the entire study duration. A similar pattern was observed for density-dependence, with relatively stronger negative effects of density on productivity than on survival. Our novel modeling approach required an informative prior but was successful at updating the prior distribution for juvenile survival. Our results show that integrated population models provide an attractive and flexible method for directly modeling all relevant density-dependent processes and for combining breeding and post-breeding data to estimate juvenile survival in the absence of direct data., Competing Interests: The authors declare that they have no competing interests., (© 2024 Lewis et al.)

Abstract Mutualisms are ubiquitous in nature, provide important ecosystem services, and involve many species of interest for conservation. Theoretical progress on the population dynamics of mutualistic interactions, however, comparatively lagged behind that of trophic and competitive interactions, leading to the impression that ecologists still lack a generalized framework to investigate the population dynamics of mutualisms. Yet, over the last 90 years, abundant theoretical work has accumulated, ranging from abstract to detailed. Here, we review and synthesize historical models of two‐species mutualisms. We find that population dynamics of mutualisms are qualitatively robust across derivations, including levels of detail, types of benefit, and inspiring systems. Specifically, mutualisms tend to exhibit stable coexistence at high density and destabilizing thresholds at low density. These dynamics emerge when benefits of mutualism saturate, whether due to intrinsic or extrinsic density dependence in intraspecific processes, interspecific processes, or both. We distinguish between thresholds resulting from Allee effects, low partner density, and high partner density, and their mathematical and conceptual causes. Our synthesis suggests that there exists a robust population dynamic theory of mutualism that can make general predictions.

Abstract Studies of spatial point patterns (SPPs) are often used to examine the role that density‐dependence (DD) and environmental filtering (EF) play in community assembly and species coexistence in forest communities. However, SPP analyses often struggle to distinguish the opposing effects that DD and EF may have on the distribution of tree species. We tested percolation threshold analysis on simulated tree communities as a method to distinguish the importance of thinning from DD EF on SPPs. We then compared the performance of percolation threshold analysis results and a Gibbs point process model in detecting environmental associations as well as clustering patterns or overdispersion. Finally, we applied percolation threshold analysis and the Gibbs point process model to observed SPPs of 12 dominant tree species in a Puerto Rican forest to detect evidence of DD and EF. Percolation threshold analysis using simulated SPPs detected a decrease in clustering due to DD and an increase in clustering from EF. In contrast, the Gibbs point process model clearly detected the effects of EF but only identified DD thinning in two of the four types of simulated SPPs. Percolation threshold analysis on the 12 observed tree species' SPPs found that the SPPs for two species were consistent with thinning from DD processes only, four species had SPPs consistent with EF only and SPP for five reflected a combination of both processes. Gibbs models of observed SPPs of living trees detected significant environmental associations for 11 species and clustering consistent with DD processes for seven species. Percolation threshold analysis is a robust method for detecting community assembly processes in simulated SPPs. By applying percolation threshold analysis to natural communities, we found that tree SPPs were consistent with thinning from both DD and EF. Percolation threshold analysis was better suited to detect DD thinning than Gibbs models for clustered simulated communities. Percolation threshold analysis improves our understanding of forest community assembly processes by quantifying the relative importance of DD and EF in forest communities.

Abstract Dispersive movements are often thought to be multicausal and driven by individual body size, sex, conspecific density, environmental variation, personality, and/or other variables. Yet such variables often do not account for most of the variation among dispersive movements in nature, leaving open the possibility that dispersion may be indeterministic. We assessed the amount of variation in 24 h movement distances that could be accounted for by potential drivers of displacement with a large empirical dataset of movement distances performed by Fowler's Toads (Anaxyrus fowleri) on the northern shore of Lake Erie at Long Point, Ontario (2002–2021, incl.). These toads are easy to sample repeatedly, can be identified individually and move parallel to the shoreline as they forage at night, potentially dispersing to new refuge sites. Using a linear mixed‐effect model that incorporated random effect terms to account for sampling variance and inter‐annual variation, we found that all potential intrinsic and extrinsic drivers of movement accounted for virtually none of the variation observed among 24 h distances moved by these animals, whether over short or large spatial scales. We examined the idea of movement personality by testing variance per individual toad and found no evidence of individuality in movement distances. We conclude that deterministic variables, whether intrinsic or extrinsic, neither can be shown to nor are necessary to drive movements in this population over all spatial scales. Stochastic, short time‐scale movements, such as daily foraging movements, can instead accumulate over time to produce large spatial‐scale movements that are dispersive in nature.

The extent and magnitude of parasitism often vary among closely related host species and across populations within species. Determining the ecological basis for this species and population‐level variation in parasitism is critical for understanding infection dynamics in multi‐host–parasite systems. To investigate such ecological underpinnings of variation in parasitism, we studied Enallagma damselfly host species and their water mite (Arrenurus spp.) ectoparasites in lakes.We first evaluated how host identity and density could shape parasitism. To test the effects of con‐ and heterospecific host density on parasitism, we used a field experiment with Enallagma basidens and E. signatum. We found that parasitism did not vary with con‐ or heterospecific density and was determined by host identity alone, with no spillover effects.We also evaluated the potential role of local adaptation and resource availability in shaping parasitism. To do so, we used E. signatum in a reciprocal transplant experiment crossed with a prey resource‐level manipulation. This experiment revealed that parasitism declined sharply for one host population in its non‐local lake, but not the other source population, with no effects of prey levels. This asymmetry implies that damselflies express enhanced defences against parasitism that are neither population‐specific nor dependent on resource abundance, or that mites developed heightened local host specificity.The results of multivariate modeling from an observational study generally supported these experimental findings: neither host density nor resource abundance strongly explained among‐population variation in parasitism. Instead, local abiotic conditions (pH) had the strongest relationship with parasitism, with minimal associations with predator density, temperature and a measure of immune function.Collectively, our findings suggest a crucial role for the local environment in shaping host–parasite interactions within multi‐host–parasite systems. More generally, these results show that research at the intersection of community ecology and disease ecology is critical for understanding host–parasite dynamics within natural communities. [ABSTRACT FROM AUTHOR]

Ecologists often estimate population trends of animals in time series of counts using linear regression to estimate parameters in a linear transformation of multiplicative growth models, where logarithms of rates of change in counts in time intervals are used as response variables. We present quantile regression estimates for the median (0.50) and interquartile (0.25, 0.75) relationships as an alternative to mean regression estimates for common density‐dependent and density‐independent population growth models. We demonstrate that the quantile regression estimates are more robust to outliers and require fewer distributional assumptions than conventional mean regression estimates and can provide information on heterogeneous rates of change ignored by mean regression. We provide quantile regression trend estimates for 2 populations of greater sage‐grouse (Centrocercus urophasianus) in Wyoming, USA, and for the Crawford population of Gunnison sage‐grouse (Centrocercus minimus) in southwestern Colorado, USA. Our selected Gompertz models of density dependence for both populations of greater sage‐grouse had smaller negative estimates of density‐dependence terms and less variation in corresponding predicted growth rates (λ) for quantile than mean regression models. In contrast, our selected Gompertz models of density dependence with piecewise linear effects of years for the Crawford population of Gunnison sage‐grouse had predicted changes in λ across years from quantile regressions that varied more than those from mean regression because of heterogeneity in estimated λs that were both less and greater than mean estimates. Our results add to literature establishing that quantile regression provides better behaved estimates than mean regression when there are outlying growth rates, including those induced by adjustments for zeros in the time series of counts. The 0.25 and 0.75 quantiles bracketing the median provide robust estimates of population changes (λ) for the central 50% of time series data and provide a 50% prediction interval for a single new prediction without making parametric distributional assumptions or assuming homogeneous λs. Compared to mean estimates, our quantile regression trend estimates for greater sage‐grouse indicated less variation in density‐dependent λs by minimizing sensitivity to outlying values, and for Gunnison sage‐grouse indicated greater variation in density‐dependent λs associated with heterogeneity among quantiles. [ABSTRACT FROM AUTHOR]

The ringed seal is a small phocid seal that has a northern circumpolar distribution. It has long been recognized that body size is variable in ringed seals, and it has been suggested that ecotypes that differ in size exist. This study explores patterns of body size (length and girth) and age-at-maturity across most of the Arctic subspecies’ range using morphometric data from 35 sites. Asymptotic lengths varied from 113 to 151 cm, with sites falling into five distinct size clusters (for each sex). Age-at-maturity ranged from 3.1 to 7.4 years, with sites that had early ages of sexual maturity generally having small length-at-maturity and small final body length. The sexes differed in length at some sites, but not in a consistent pattern of dimorphism. The largest ringed seals occurred in western Greenland and eastern Canada, and the smallest occurred in Alaska and the White Sea. Latitudinal trends occurred only within sites in the eastern Canadian Arctic. Girth (with length and season accounted for) was also highly variable but showed no notable spatial pattern; males tended to be more rotund than females. Genetic studies are needed, starting with the “giants” at Kangia (Greenland) and in northern Canada to determine whether they are genetically distinct ecotypes. Additional research is also needed to understand the ecological linkages that drive the significant regional size differences in ringed seals that were confirmed in this study, and also to understand their implications with respect to potential adaptation to climate change.

Wildlife populations cannot grow indefinitely; however, natural mechanisms of population regulation may be unknown for species undergoing prolonged harvest or persecution. Poached across the continent for centuries, African elephants have seldom been subject to natural mechanisms of population regulation. However, increased protections have removed the top-down control of poaching, leading some elephant populations to rebound. Maintaining healthy populations and ecosystems throughout the elephant's range requires a better understanding of the natural ways in which elephant populations are regulated. We analyzed 24 years of data on an African savanna elephant (Loxodonta africana) population in Tanzania, finding rapid and sustained population growth immediately following cessation of poaching. Annual survival was high and contributed 15.2 times more to population growth than recruitment. An upward shifting age structure, high elephant densities and anthrax outbreaks were negatively associated with survival, representing 62.4 % of variable importance. This suggests that disease is a key density-dependent mechanism for regulating elephant populations, capable of rapid population stabilization. However, patterns of anthrax outbreaks are variable across elephant populations, necessitating a better understanding of the diversity and drivers of anthrax outbreaks, and effects on elephant vital rates. Although rainfall has been suggested as an important factor for anthrax outbreak frequency and severity, we found no evidence for mediation of anthrax effects by rainfall in our survival models. Nevertheless, managers should be aware of the natural mechanisms of elephant population regulation, including disease-related feedbacks, and the potential role of changing precipitation patterns, when making decisions for elephant conservation and management throughout Africa. [ABSTRACT FROM AUTHOR]

Dispersal is a key demographic process involving three stages: emigration, transience and settlement; each of which is influenced by individual, social and environmental determinants. An integrated understanding of species dispersal is essential for demographic modelling and conservation planning. Here, we review the dispersal patterns and determinants documented in the scientific literature for the grey wolf (Canis lupus) across its distribution range. We showed a surprisingly high variability within and among study areas on all dispersal parameters – dispersal rate, direction, distance, duration and success. We found that such large variability is due to multiple individual, social and environmental determinants, but also due to previously overlooked methodological research issues. We revealed a potential non‐linear relationship between dispersal rate and population density, with dispersal rate higher at both ends of the gradient of population density. We found that human‐caused mortality reduces distance, duration and success of dispersal events. Furthermore, dispersers avoid interaction with humans, and highly exposed areas like agricultural lands hamper population connectivity in many cases. We identified numerous methodological research problems that make it difficult to obtain robust estimates of dispersal parameters and robust inferences on dispersal patterns and their determinants. In particular, analyses where confounding factors were not accounted for led to substantial knowledge gaps on all aspects of dispersal in an otherwise much‐studied species. Our understanding of wolf biology and management would significantly benefit if wolf dispersal studies reported the results and possible factors affecting wolf dispersal more transparently. [ABSTRACT FROM AUTHOR]