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Wood in the deep sea serves as a substantial food source in an otherwise barren environment, forming specialized, endemic, and diverse community assemblages. This biodiversity reliance on a terrestrial source creates a linkage by which anthropogenic impacts on land can alter the deep oceans. Knowledge of the alpha‐ or beta‐diversity of entire wood‐fall communities, and wooden drivers of each would elucidate the terrestrial and deep‐sea linkage. We report on a multifactorial experiment in the deep ocean in which alpha‐ and beta‐diversity of 43 wood falls and 11 tree species are quantified over time, wood density, and wood size. We tested multiple hypotheses seeking to link how biodiversity on land may impact the biodiversity in the deep oceans. A tremendous biodiversity occurred among these wood falls in the deep Gulf of Mexico; 114 invertebrate species from 10 phyla. Time, wood hardness, and wood size all impacted various components of community structure. In many cases, these effects were additive. Species occurring on softwoods versus hardwoods and small versus large wood falls were compositionally different. Although various processes can control community structure, this experiment suggests a strong influence of environmental filtering and host specificity of wood‐fall invertebrates suggesting an intimate coupling to tree biodiversity and biomass on land. [ABSTRACT FROM AUTHOR]

A fundamental question in ecology is which species will prevail over others amid changes in both environmental mean conditions and their variability. Although the widely accepted fluctuating resource hypothesis predicts that increases in mean resource availability and variability therein will promote nonnative plant invasion, it remains unclear to what extent these effects might be mediated by soil microbes. We grew eight invasive nonnative plant species as target plants in pot-mesocosms planted with five different synthetic native communities as competitors, and assigned them to eight combinations of two nutrient-fluctuation (constant vs. pulsed), two nutrient-availability (low vs. high) and two soil-microbe (living vs. sterilized) treatments. We found that when plants grew in sterilized soil, nutrient fluctuation promoted the dominance of nonnative plants under overall low nutrient availability, whereas the nutrient fluctuation had minimal effect under high nutrient availability. In contrast, when plants grew in living soil, nutrient fluctuation promoted the dominance of nonnative plants under high nutrient availability rather than under low nutrient availability. Analysis of the soil microbial community suggests that this might reflect that nutrient fluctuation strongly increased the relative abundance of the most dominant pathogenic fungal family or genus under high nutrient availability, while decreasing it under low nutrient availability. Our findings are the first to indicate that besides its direct effect, environmental variability could also indirectly affect plant invasion via changes in soil microbial communities. [ABSTRACT FROM AUTHOR]

Niche modeling is typically used to assess the effects of anthropogenic land use and climate change on species distributions and to inform spatial conservation planning. These models focus on the suitability of local biotic and abiotic conditions for a species in environmental space (E‐space). Although movements also affect species occurrence, efforts to formally integrate geographic space (G‐space) into niche modeling have been hindered by the lack of comprehensive theoretical frameworks. We propose the "functional habitat" framework to define areas that are simultaneously of high quality in E‐space, and functionally connected to other suitable habitats in G‐space. Originating in metapopulation ecology, approaches have been developed to assess the amount of suitable connected habitats, based on the proximity between pairs of locations. Using network theory, which operates in topological space (T‐space, defined by a network), we extended these metapopulation approaches to integrate movement constraints in G‐space with niche modeling in E‐space. We demonstrate the functional habitat framework using empirical data (GPS tracking and population monitoring) throughout the European wild mountain reindeer (Rangifer t. tarandus) distribution range. We show that functional habitat outperforms traditional suitability in explaining the species' distribution. This approach integrates effects from habitat loss and fragmentation for spatial conservation planning, and avoids overemphasizing small, inaccessible areas with locally suitable habitats. The functional habitat framework formally integrates biotic, abiotic, and movement constraints in niche modeling using network theory, thus opening a wide range of applications in spatial conservation planning. [ABSTRACT FROM AUTHOR]

The subject loggerhead appeared to dominate the smaller green and Kemp's ridley turtles (e.g., biting at rear flippers), whereas the larger loggerhead dominated the subject loggerhead (Schofield et al., [14]). Keywords: animal-borne video; competition; Gulf of Mexico; loggerhead; niche; sea turtle EN animal-borne video competition Gulf of Mexico loggerhead niche sea turtle 1 5 5 01/04/23 20230101 NES 230101 The competitive exclusion principle states that ecologically similar species sharing a niche cannot occupy the same space at the same time (Gause, [5]). The larger loggerhead's aggressive behavior toward the subject loggerhead, but apparently not toward the green turtles and Kemp's ridley turtles, might reflect an intraspecific response (Dujon et al., [2]; Schofield et al., [15]). [Extracted from the article]

Plant communities are predicted to be more resistant to invasion if they are highly productive, harbor species with similar functional traits to invaders, or support species with high competitive potential. However, the strength of competition may decrease with increasing abiotic stress if species more heavily invest in traits that confer stress tolerance over competitive ability, potentially influencing community trait–resistance relationships. Recent research examining how community traits influence invasion resistance has been predominantly focused on single vegetation types, and results between studies are often conflicting. Few studies have evaluated the extent to which abiotic factors and community traits interact to influence invasion along vegetation gradients. Here, we use an in situ seed addition experiment to examine how above‐ and below‐ground plant traits and vegetation type interact to influence community resistance to invasion by a recently introduced annual grass, Ventenata dubia, along a productivity gradient in eastern Oregon, USA. To measure invasion resistance, we evaluated V. dubia biomass in seeded subplots with varying trait compositions across three vegetation types situated along a productivity gradient: scab‐flats (sparsely vegetated dwarf‐shrublands), low sage‐steppe, and ephemeral wet meadows. Trait–resistance relationships were highly context dependent. In wet meadows (the most productive sites), resistance to invasion increased with increasing resident biomass and as community weighted mean trait values for specific leaf area, fine‐to‐total root volume, and height become more similar to V. dubia's trait values, although these relationships were relatively weak. We did not find evidence that neighboring species influenced invasion resistance in less productive vegetation types, in contrast to our expectations that facilitative interactions may increase with decreasing productivity as posited by the stress‐gradient hypothesis. Unlike V. dubia, which heavily invaded all three vegetation types, introduced species with similar trait values, including Bromus tectorum, were not abundant throughout the study area demonstrating V. dubia's unique ability to take advantage of available resources. Our results illustrate how community traits and site productivity interact to influence community resistance to invasion and highlight that communities with lower overall biomass and few functionally similar species to V. dubia may be at the greatest risk for invasion. [ABSTRACT FROM AUTHOR]

Generalist species are the linchpins of networks, as they are important for maintaining network structure and function. Previous studies have shown that interactions between generalists tend to occur consistently across years and sites. However, the link between temporal and spatial interaction persistence across scales remains unclear. To address this gap, we collected data on plant–pollinator interactions throughout the flowering period for 5 yr across six plots in a subalpine meadow in the Rocky Mountains. We found that interactions between generalists tended to persist more in time and space such that interactions near the network core were more frequently recorded across years, within seasons, and among plots. We posit that species' tolerance of environmental variation across time and space plays a key role in generalization by regulating spatiotemporal overlap with interaction partners. Our results imply a role of spatiotemporal environmental variation in organizing species interactions, marrying niche concepts that emphasize species environmental constraints and their community role. [ABSTRACT FROM AUTHOR]

Climate and competition interact to affect species' performance, such as growth and survival, and help determine species distributions and coexistence. However, it is unclear how climatic conditions modulate frequency‐dependent performance, that is, how performance changes as a species becomes locally rare or common. This is critical because declines in performance as a species becomes more common (negative frequency dependence) is a signature of niche differences among species that stabilize coexistence, whereas positive frequency dependence leads to priority effects and hampers species coexistence. Here, we used dendrochronology and hierarchical models to test whether frequency‐dependent growth of sugar pine (Pinus lambertiana) depends on climatic conditions. We found that growth rates were strongly dependent on annual precipitation, but no frequency dependence was evident across all years. However, there was a strong interaction between precipitation and frequency dependence, revealing stabilizing niche differences in dry years but positive frequency dependence in wet years. These differences emerged because of precipitation‐driven changes in the direction and strength of both con‐ and heterospecific competition. Overall, these results show how stabilizing and destabilizing effects can be temporally dynamic for long‐lived species and interact with climate variation. [ABSTRACT FROM AUTHOR]

The role of light in partitioning ecological niche space remains a frontier in understanding the assembly of terrestrial vertebrate communities and their response to global change. Leveraging recent advances in biologging technology and intensive field surveys of cloud forest bird communities across an agricultural land use gradient in the Peruvian Andes, we demonstrate that eye size predicts (1) the ambient light microenvironment used by free‐ranging birds, (2) their foraging niche, and (3) species‐specific sensitivity to agricultural land use change. For 15 species carrying light sensors (N = 71 individuals), light intensity levels were best explained by eye size and foraging behavior, with larger‐eyed species using darker microenvironments. Across the cloud forest bird community (N = 240 species), hyperopic ("far‐sighted") foragers, (e.g., flycatchers), had larger eyes compared to myopic ("near‐sighted") species (e.g., gleaners and frugivores); eye size was also larger for myopic insectivores that foraged in the forest understory. Eye size strongly predicted sensitivity to brightly lit habitats across an agricultural land use gradient. Species that increased in abundance in mixed intensity agriculture, including fencerows, silvopasture, and pasture, had smaller eyes, suggesting that light acts as an environmental filter when communities disassemble in a human‐disturbed landscape. We suggest that eye size represents a novel functional trait contributing to terrestrial vertebrate community assembly and sensitivity to habitat disturbance. [ABSTRACT FROM AUTHOR]

Behavioral niche partitioning is an important and widely assumed mechanism for the coexistence of ecologically similar species. Here we assessed this mechanism by testing its core assumption, that evolved differences in foraging behavior correspond with differences in resources consumed. We combined data on foraging behavior, available prey, and observed diets of five coexisting species of New World wood warblers (Parulidae), a system that has been foundational to our understanding of behavioral niche partitioning. Consistent with past work, we found that the five species differed markedly in their foraging behavior, enough that some species pairs hardly overlapped at all in foraging microhabitat. In contrast, the birds overlapped highly in diet, while exhibiting small, interpretable differences in resource use. The high overlap resulted mostly from all five species consuming numerous ants, a prey source that moves between microhabitats. To test the prediction that the large differences in foraging behavior explain the small dietary differences, we generated expected diets based on available prey and foraging microhabitat use. Consistent with niche partitioning as a coexistence mechanism, we found that the small dietary differences were explained by a combination of foraging microhabitat and available prey, but this pattern was driven by only a small number of prey taxa. Thus, we found mixed support for behavioral niche partitioning. Our results indicate that foraging behavior among these bird species helps explain subtle variation in diet, potentially facilitating coexistence. However, our results also revealed a weak relationship between foraging behavior and resource partitioning. Consequently, studies that rely solely on foraging behavior may greatly overestimate the degree of niche differentiation leading to erroneous conclusions. Overall, this study calls into question how and why these differences in foraging behavior evolved, and what role if any they play in facilitating coexistence. [ABSTRACT FROM AUTHOR]

Invasive ecosystem engineers both positively and negatively affect their recipient ecosystems by generating novel habitats. Many studies have focused on alterations to ecosystem properties and to native species diversity and abundance caused by invasive engineers. However, relatively few studies have documented the extent to which behaviors of native species are affected. The red seaweed Gracilaria vermiculophylla (Rhodophyta) invaded estuaries of the southeastern United States within the last few decades and now provides abundant aboveground vegetative cover on intertidal mudflats that were historically devoid of seaweeds. We hypothesized that G. vermiculophylla would affect the foraging behavior of native shorebirds positively for birds that target seaweed‐associated invertebrates or negatively for birds that target prey on or within the sediment now covered with seaweed. Visual surveys of mudflats >1 ha in size revealed that more shorebirds occurred on mudflats with G. vermiculophylla relative to mudflats without G. vermiculophylla. This increased density was consistent across 7 of 8 species, with the one exception being the semipalmated plover Charadrius semipalmatus. A regression‐based analysis indicated that while algal presence predicted shorebird density, densities of some bird species depended on sediment composition and infaunal invertebrate densities. At smaller spatial scales (200 m2 and <1 m2), experimental removals and additions of G. vermiculophylla and focal observations showed strong variation in behavioral response to G. vermiculophylla among bird species. Birds preferentially foraged in bare mud (e.g., C. semipalmatus), in G. vermiculophylla (e.g., Arenaria interpres), or displayed no preference for either habitat (e.g., Tringa semipalmata). Thus, while the presence of the invasive ecosystem engineer on a mudflat appeared to attract greater numbers of these predators, shorebird species differed in their behavioral responses at the smaller spatial scales that affect their foraging. Our research illuminates the need to account for species identity, individual behavior, and scale when predicting the impacts of invasive species on native communities. [ABSTRACT FROM AUTHOR]

A fundamental question in ecology is which species will prevail over others amid changes in both environmental mean conditions and their variability. Although the widely accepted fluctuating resource hypothesis predicts that increases in mean resource availability and variability therein will promote nonnative plant invasion, it remains unclear to what extent these effects might be mediated by soil microbes. We grew eight invasive nonnative plant species as target plants in pot-mesocosms planted with five different synthetic native communities as competitors, and assigned them to eight combinations of two nutrient-fluctuation (constant vs. pulsed), two nutrient-availability (low vs. high) and two soil-microbe (living vs. sterilized) treatments. We found that when plants grew in sterilized soil, nutrient fluctuation promoted the dominance of nonnative plants under overall low nutrient availability, whereas the nutrient fluctuation had minimal effect under high nutrient availability. In contrast, when plants grew in living soil, nutrient fluctuation promoted the dominance of nonnative plants under high nutrient availability rather than under low nutrient availability. Analysis of the soil microbial community suggests that this might reflect that nutrient fluctuation strongly increased the relative abundance of the most dominant pathogenic fungal family or genus under high nutrient availability, while decreasing it under low nutrient availability. Our findings are the first to indicate that besides its direct effect, environmental variability could also indirectly affect plant invasion via changes in soil microbial communities., (© 2023 The Ecological Society of America.)

Abstract: Habitat complexity is accepted as a general mechanism for increasing the abundance and diversity of communities. However, the circumstances under which complexity has the strongest effects are not clear. Over 20 degrees of Australia's east coast, we tested whether the effects of within‐site structural habitat complexity on the diversity and community structure of sessile marine invertebrates was consistent over a latitudinal gradient where environmental conditions and species composition vary. We used experimental arrays with varied structural treatments to detect whether community cover, species richness, diversity and community composition (β‐diversity) changed with increasing complexity. Community response to complexity varied over latitude due to differences in species richness and community development. Increased complexity had the greatest positive effects on community cover and species richness at higher latitudes where recruitment and growth were low. At lower latitudes, community cover and species richness were higher overall and did not vary substantially between complexity treatments. Latitudinal variation in within‐treatment β‐diversity relative to complexity further suggest divergent community responses. At higher latitudes, increased similarity in more complex treatments suggests community dominance of successful taxonomic groups. Despite limited effects on species richness and community cover at lower latitudes, β‐diversity was higher in more complex treatments, signifying potential positive effects of increased complexity at these sites. These results demonstrate the context‐dependency of complexity effects in response to variation in species richness and community development and should be taken into consideration to help direct conservation and restoration efforts. [ABSTRACT FROM AUTHOR]

The emergent properties of the collection of species in a natural community, such as diversity and the distribution of relative abundances, are influenced by both niche-based and neutral (stochastic) processes. This pluralistic view of the natural world reconciles theory with empirical observations better than does either a strictly niche- or neutrality-based perspective. Even so, rules (or rules of thumb) that govern the relative contributions that niche-based and stochastic processes make as communities assemble remain only vaguely formulated and incompletely tested. For example, the translation of non-random (non-neutral) ecological processes, which differentially sort among species within a community, into species-compositional patterns may occur more influentially within some demographic subsets of organisms than within others. In other words, the relative contributions of niche vs. neutral processes may vary among age-, size-, or stage-classes. For example, non-random patterns of mortality that occur among seedlings in a rain forest, or among newly settled juveniles in communities of sessile marine communities, could be more influential than non-random mortality during later stages in determining overall community diversity. We propose two alternative, mutually compatible, hypotheses to account for different levels of influence from mortality among life-cycle stages toward producing non-random patterns in organismal communities. The Turnover Model simply posits that those demographic classes characterized by faster rates of turnover contribute greater influence in the short-term as sufficient mortality gives rise to non-random changes to the community, as well as over the longer-term as multiple individuals of a given fast-turnover demographic class transition into later classes compared to each individual that ratchets from a slow-turnover starting class into a later class. The Turnover Model should apply to most communities of organisms. The Niche Model, which posits that niche-based processes are more influential in some demographic classes relative to others, may alternatively or additionally apply to communities. We also propose several alternative mechanisms, especially relevant to forest trees, that could cause dynamics consistent with the Niche Model. These mechanisms depend on differences among demographic classes in the extent of demographic variation that individual organisms experience through their trait values or neighborhood conditions. [ABSTRACT FROM AUTHOR]

Four metacommunity paradigms-usually called neutral, species sorting, mass effects, and patch dynamics, respectively-are widely used for empirical and theoretical studies of spatial community dynamics. The paradigm framework highlights key ecological mechanisms operating in metacommunities, such as dispersal limitation, competition-colonization tradeoffs, or species equivalencies. However, differences in coexistence mechanisms between the paradigms and in situations with combined influences of multiple paradigms are not well understood. Here, we create a common model for competitive metacommunities, with unique parameterizations for each metacommunity paradigm and for scenarios with multiple paradigms operating simultaneously. We derive analytical expressions for the strength of Chesson's spatial coexistence mechanisms and quantify these for each paradigm via simulation. For our model, fitness-density covariance, a concentration effect measuring the importance of intraspecific aggregation of individuals, is the dominant coexistence mechanism in all three niche-based metacommunity paradigms. Increased dispersal between patches erodes intraspecific aggregation, leading to lower coexistence strength in the mass effects paradigm compared to species sorting. Our analysis demonstrates the potential importance of aggregation of individuals (fitness-density covariance) over co-variation in abiotic environments and competition between species (the storage effect), as fitness-density covariance can be stronger than the storage effect and is the sole stabilizing mechanism in the patch dynamics paradigm. As expected, stable coexistence does not occur in the neutral paradigm, which requires species to be equal and emphasizes the role of stochasticity. We show that stochasticity also plays an important role in niche-structured metacommunities by altering coexistence strength. We conclude that Chesson's spatial coexistence mechanisms provide a flexible framework for comparing metacommunities of varying complexity. [ABSTRACT FROM AUTHOR]

To determine whether phylogenetic relatedness predicts ecological niche differences and community assembly in the field, we transplanted 16 focal plant species into field niches of species of increasing phylogenetic relatedness, manipulated the presence of plant neighbors, and measured environmental covariates. We found that plant survivorship declined with increasing phylogenetic distance in the presence of neighbors, but with neighbor removal, reached a low point in field niches occupied by species diverged at 63 My, the maximum age of confamilials in our study, and then increased again in the sites of distant relatives. Plant biomass was similarly nonlinear, and niche differences increased with neighbor removal. Competitive response showed a linear decline with relatedness. We compared our experimental results to natural community composition, finding that conspecifics and distant relatives were more likely to co-occur at smaller spatial scales, as predicted by our measures of performance. [ABSTRACT FROM AUTHOR]

Climate and competition are often presented from two opposing views of the dominant driver of individual tree growth and species distribution in temperate forests, such as those in the eastern United States. Previous studies have provided abundant evidence indicating that both factors influence tree growth, and we argue that these effects are not independent of one another and rather that interactions between climate, competition, and size best describe tree growth. To illustrate this point, we describe the growth responses of five common eastern tree species to interacting effects of temperature, precipitation, competition, and individual size using maximum likelihood estimation. Models that explicitly include interactions among these four factors explained over half of the variance in annual growth for four out of five species using annual climate. Expanding temperature and precipitation analyses to include seasonal interactions resulted in slightly improved models with a mean R2 of 0.61 ( SD 0.10). Growth responses to individual factors as well their interactions varied greatly among species. For example, growth sensitivity to temperature for Quercus rubra increased with maximum annual precipitation, but other species showed no change in sensitivity or slightly reduced annual growth. Our results also indicate that three-way interactions among individual stem size, competition, and temperature may determine which of the five co-occurring species in our study could have the highest growth rate in a given year. Continued consideration and quantification of interactions among climate, competition, and individual-based characteristics are likely to increase understanding of key biological processes such as tree growth. Greater parameterization of interactions between traditionally segregated factors such as climate and competition may also help build a framework to reconcile drivers of individual-based processes such as growth with larger-scale patterns of species distribution. [ABSTRACT FROM AUTHOR]

Many established models of animal foraging assume that individuals are ecologically equivalent. However, it is increasingly recognized that populations may comprise individuals who differ consistently in their diets and foraging behaviors. For example, recent studies have shown that individual foraging site fidelity (IFSF, when individuals consistently forage in only a small part of their population's home range) occurs in some colonial breeders. Short-term IFSF could result from animals using a win--stay, lose--shift foraging strategy. Alternatively, it may be a consequence of individual specialization. Pelagic seabirds are colonial central-place foragers, classically assumed to use flexible foraging strategies to target widely dispersed, spatiotemporally patchy prey. However, tracking has shown that IFSF occurs in many seabirds, although it is not known whether this persists across years. To test for long-term IFSF and to examine alternative hypotheses concerning its cause, we repeatedly tracked 55 Northern Gannets (Morus bassanus) from a large colony in the North Sea within and across three successive breeding seasons. Gannets foraged in neritic waters, predictably structured by tidal mixing and thermal stratification, but subject to stochastic, wind-induced overturning. Both within and across years, coarse to mesoscale (tens of kilometers) IFSF was significant but not absolute, and foraging birds departed the colony in individually consistent directions. Carbon stable isotope ratios in gannet blood tissues were repeatable within years and nitrogen ratios were also repeatable across years, suggesting long-term individual dietary specialization. Individuals were also consistent across years in habitat use with respect to relative sea surface temperature and in some dive metrics, yet none of these factors accounted for IFSF. Moreover, at the scale of weeks, IFSF did not decay over time and the magnitude of IFSF across years was similar to that within years, suggesting that IFSF is not primarily the result of win--stay, lose--shift foraging. Rather, we hypothesize that site familiarity, accrued early in life, causes IFSF by canalizing subsequent foraging decisions. Evidence from this and other studies suggests that IFSF may be common in colonial central-place foragers, with farreaching consequences for our attempts to understand and conserve these animals in a rapidly changing environment. [ABSTRACT FROM AUTHOR]

Theoretical studies have shown that coexistence between competitors can be favored in a spatially heterogeneous environment by a number of mechanisms, which ultimately allow the expression of persistent or transitory variation in species competitive abilities, colonization, or reproduction. Four distinctive paradigms to model metacommunities have been identified according to assumptions about the biology of the species and essential aspects of the environment. Missing from these are mechanisms of coexistence that can arise from the dispersal process itself without explicit spatial heterogeneity or biological trade-offs. These mechanisms have only recently received attention, but they may be common in marine communities and other systems in which dispersal is obligatory and modulated by the physical environment. We investigate coexistence in spatially homogeneous metacommunities where there is no partitioning of resources, no competition-colonization trade-off, and no possibility of source-sink dynamics. Coexistence is shown to be possible through three distinct mechanisms related to the dispersal process itself. Firstly, in a neutral scenario, inclusion of temporal variability in the connectivity matrix, emulating an intrinsic attribute of ocean character and other turbulent environments, can promote the invasion of an equally matched competitor and, in a hierarchical competition scenario, the persistence of an otherwise unviable, inferior competitor (the dispersal variability mechanism). Secondly, a sufficiently large difference in the shape of the time-independent dispersal kernels of the two species, which may result from differences in larval-release timing, buoyancy, or behavior, can produce stable coexistence in the center of their shared range (the dispersal-shape mechanism). Thirdly, asymmetry in the dispersal process due to biased advection renders the metapopulation model reactive, such that small variations in the upstream abundances can be sufficient for the subordinate species to stably persist (the dispersal-bias mechanism). These results demonstrate that a subordinate species may persist by occupying a dispersal niche that differs sufficiently from that of the dominant species. Further theoretical research is necessary to develop simple empirical tests for these and other dispersal-based coexistence mechanisms. [ABSTRACT FROM AUTHOR]

Ecosystem-wide primary productivity generally increases with primary producer diversity, emphasizing the importance of diversity for ecosystem function. However, most studies that demonstrate this positive relationship have focused on terrestrial and aquatic benthic systems, with little attention to the diverse marine pelagic primary producers that play an important role in regulating global climate. Here we show how phytoplankton biodiversity enhances overall marine ecosystem primary productivity and other ecosystem functions using a self-organizing ecosystem model. Diversity manipulation numerical experiments reveal positive, asymptotically saturating relationships between ecosystem-wide phytoplankton diversity and functions of productivity, nutrient uptake, remineralization, and diversity metrics used to identify mechanisms shaping these relationships. Increase in productivity with increasing diversity improves modeled ecosystem stability and model robustness and leads to productivity rates that exceed expected yields primarily through niche complementarity and facilitative interactions between coexisting phytoplankton types; the composition of traits in assemblages determines the magnitude of complementarity and selection effects. While findings based on these aggregate measures of diversity effects parallel those from the majority of experimental outcomes of terrestrial and benthic biodiversity-ecosystem function studies, we combine analyses of community diversity effects and investigations of the underlying interactions among phytoplankton types to demonstrate how an increase in recycled production of non-diatoms through an increase in new production of diatoms drives this diversity-ecosystem function response. We demonstrate the important role that facilitation plays in the modeled marine plankton and how this facilitative interaction could amplify future climate-driven changes in ocean ecosystem productivity. [ABSTRACT FROM AUTHOR]

Whether species will be extirpated in their current geographic ranges due to rapidly changing climate, and if so, whether they can avoid extinction by shifting their distributions are pressing questions for biodiversity conservation. However, forecasts of climate change impacts on species' geographic distributions rarely incorporate a demographic understanding of species' responses to climate. Because many biotic and abiotic factors at multiple scales control species' range limits, experimentation is essential to establish underlying mechanisms. We used a manipulative climate change experiment embedded within a natural climate gradient to examine demographic responses of 12 prairie species with northern range limits within the Pacific Northwest, USA. During the first year, warming decreased recruitment of species even at the coolest edge of their current ranges, but this effect disappeared when they were moved poleward beyond their current ranges. This response was largely driven by differences in germination rates. Other vital rates responded in unique and sometimes opposing ways (survivorship vs. fitness) to species' current ranges and climate change, and were mediated by indirect effects of climate on competition and nutrient availability. Our results demonstrate the importance of using regional-scale climate manipulations and the need for longer-term experiments on the demographic responses that control species' distributions. [ABSTRACT FROM AUTHOR]

Foliose lichens with cyanobacterial bionts (bipartite and tripartite) form a distinct assemblage of epiphytes strongly associated with humid microclimatic conditions in inland British Columbia. Previous research showed that these cyano- and cephalolichen communities are disproportionately abundant and species-rich on conifer saplings beneath Populus compared to beneath other tree species. More revealing, lichens with cyanobacterial bionts were observed beneath Populus even in stands that did not otherwise support them. We experimentally test the hypothesis that this association is due to the interception of glucose-rich nectar that is exuded from Populus extra-floral nectaries (EFN). Using CO2 flux measurements and phospholipid fatty acid (PLFA) analysis with experimental applications of 13C6-labeled glucose, we demonstrate that cyano- and cephalolichens have a strong respiratory response to glucose. Lichens treated with glucose had lower net photosynthesis and higher establishment rates than control thalli. Furthermore, lichens with cyanobacterial bionts rapidly incorporate exogenous 13C into lichen fatty acid tissues. A large proportion of the 13C taken up by the lichens was incorporated into fungal biomarkers, suggesting that the mycobiont absorbed and assimilated the majority of applied 13C6 glucose. Our observations suggest that both cyanolichens and cephalolichens may utilize an exogenous source of glucose, made available by poplar EFNs. The exogenous C may enable these lichens to become established by providing a source of C for fungal respiration despite drought-induced inactivity of the cyanobacterial partner. As such, the mycobiont may adopt an alternative nutritional strategy, using available exogenous carbon to extend its realized niche. [ABSTRACT FROM AUTHOR]

Recent biodiversity-ecosystem functioning experiments in temperate grasslands have shown that productivity positively correlates with plant species richness. Resource partitioning (in particular, nitrogen [N] partitioning) has been proposed as one possible mechanism to explain this pattern. There is evidence for interspecific differences in chemical form, soil depth, and timing of N uptake. However, it has rarely been tested whether such differences result in increased N exploitation at the plant community level. Using l5N-labeled litter that was mixed into different soil layers, we tested whether eight common grasses and forbs grown in communities of one, two, or four species differ with respect to the proportions of N taken up from different soil depths (N niche), and how this affects the total N uptake of plant communities. We calculated proportional similarity between species (niche overlap) with regard to N uptake from the labeled soil layers; we further calculated an a priori measure of community N uptake based on species N uptake in monoculture (community niche). Interestingly, however, plant community N uptake was not affected by species richness, possibly because community-level N uptake was determined by (diversity-independent) soil N mineralization rates. We nevertheless observed a positive effect of species richness on productivity due to increased aboveground biomass :N ratios. This may indicate increased competition for light, resulting in increased amounts of comparably N-poor stem tissue. However, community N content and biomass were positively correlated with the community niche, a measure which is strongly linked to species composition. Thus, our results suggest that the studied species are generalists rather than specialists regarding N uptake depth, and that species composition was more important than species richness in determining community N uptake. Overall, N partitioning may be a less important driver of positive biodiversity-productivity effects in temperate grasslands than previously assumed. [ABSTRACT FROM AUTHOR]

In spite of the controversy that they have generated, neutral models provide ecologists with powerful tools for creating dynamic predictions about beta-diversity in ecological communities. Ecologists can achieve an understanding of the assembly rules operating in nature by noting when and how these predictions are met or not met. This is particularly valuable for those groups of organisms that are challenging to study under natural conditions (e.g., bacteria and fungi). Here, we focused on arbuscular mycorrhizal fungal (AMF) communities and performed an extensive literature search that allowed us to synthesize the information in 19 data sets with the minimal requisites for creating a null hypothesis in terms of community dissimilarity expected under neutral dynamics. In order to achieve this task, we calculated the first estimates of neutral parameters for several AMF communities from different ecosystems. Communities were shown either to be consistent with neutrality or to diverge or converge with respect to the levels of compositional dissimilarity expected under neutrality. These data support the hypothesis that divergence occurs in systems where the effect of limited dispersal is overwhelmed by anthropogenic disturbance or extreme biological and environmental heterogeneity, whereas communities converge when systems have the potential for niche divergence within a relatively homogeneous set of environmental conditions. Regarding the study cases that were consistent with neutrality, the sampling designs employed may have covered relatively homogeneous environments in which the effects of dispersal limitation overwhelmed minor differences among AMF taxa that would lead to environmental filtering. Using neutral models we showed for the first time for a soil microbial group the conditions under which different assembly processes may determine different patterns of beta-diversity. Our synthesis is an important step showing how the application of general ecological theories to a model microbial taxon has the potential to shed light on the assembly and ecological dynamics of communities. [ABSTRACT FROM AUTHOR]

We studied the relative roles of environmental species sorting and priority effects in the assembly of ecological communities on long time scales, by analyzing community turnover of water fleas (Daphnia) in response to strong and recurrent environmental change in a fluctuating tropical lake. During the past 1800 years, Lake Naivasha (Kenya) repeatedly fluctuated between a small saline pond habitat during lowstands and a large freshwater lake habitat during highstands. Starting from a paleoecological reconstruction, we estimated the role of priority effects in Daphnia community assembly across 16 of these habitat turnovers and compared this with the response of the community to reconstructed changes in three environmental variables important for species sorting. Our results indicate that the best predictor of Daphnia community composition during highstands was the community composition just prior to the transition from lowstands to highstands. This reflects a long-lasting priority effect of late lowstand communities on highstand communities, arising when remnant lowstand populations fill newly available ecological space in the rapidly expanding lake habitat. Species sorting and priority effects had a comparable but relatively small influence on community composition during the lowstands. Moreover, these priority effects decayed rapidly with time as Daphnia communities responded to environmental change, in contrast with the highstand communities where priority effects lasted for several decades. [ABSTRACT FROM AUTHOR]

The relative importance of dispersal and niche restrictions remains a controversial topic in community ecology, especially for microorganisms that are often assumed to be ubiquitous. We investigated the impact of these factors for the community assembly of the root-symbiont arbuscular mycorrhizal fungi (AMF) by sampling roots from geothermal and nonthermal grasslands in Yellowstone National Park (YNP), followed by sequencing and RFLP of AMF ribosomal DNA. With the exception of an apparent generalist RFLP type closely related to Glomus intraradices, a distance-based redundancy analysis indicated that the AMF community composition correlated with soil pH or pH-driven changes in soil chemistry. This was unexpected, given the large differences in soil temperature and plant community composition between the geothermal and nonthermal grasslands. RFLP types were found in either the acidic geothermal grasslands or in the neutral to alkaline grasslands, one of which was geothermal. The direct effect of the soil chemical environment on the distribution of two AMF morphospecies isolated from acidic geothermal grasslands was supported in a controlled greenhouse experiment. Paraglomus occultum and Scutellospora pellucida were more beneficial to plants and formed significantly more spores when grown in acidic than in alkaline soil. Distance among grasslands, used as an estimate of dispersal limitations, was not a significant predictor of AMF community similarity within YNP, and most fungal taxa may be part of a metacommunity. The isolation of several viable AMF taxa from bison feces indicates that wide-ranging bison could be a vector for at least some RFLP types among grasslands within YNP. In support of classical niche theory and the Baas-Becking hypothesis, our results suggest that AMF are not limited by dispersal at the scale of YNP, but that the soil environment appears to be the primary factor affecting community composition and distribution. [ABSTRACT FROM AUTHOR]

Ecological communities are structured by both deterministic, niche-based processes and stochastic processes such as dispersal. A pressing issue in ecology is to determine when and for which organisms each of these types of processes is important in community assembly. The roles of deterministic and stochastic processes have been studied for a variety of communities, but very few researchers have addressed their contribution to insect herbivore community structure. Insect herbivore niches are often described as largely shaped by the antagonistic pressures of predation and host plant defenses. However host plants are frequently discrete patches of habitat, and their spatial arrangement can affect herbivore dispersal patterns. We studied the roles of predation, host plant quality, and host spatial proximity for the assembly of a diverse insect herbivore community on Quercus alba (white oak) across two growing seasons. We examined abundances of feeding guilds to determine if ecologically similar species responded similarly to variation in niches. Most guilds responded similarly to leaf quality, preferring high-nitrogen, low-tannin host plants, particularly late in the growing season, while bird predation had little impact on herbivore abundance. The communities on the high-quality plants tended to be larger and, in some cases, have greater species richness. We analyzed community composition by correlating indices of community similarity with predator presence, leaf quality similarity, and host plant proximity. Birds did not affect community composition. Community similarity was significantly associated with distance between host plants and uncorrelated with leaf quality similarity. Thus although leaf quality significantly affected the total abundance of herbivores on a host plant, in some cases leading to increased species richness, dispersal limitation may weaken this relationship. The species composition of these communities may be driven by stochastic processes rather than variation in host plant characteristics or differential predation by insectivorous birds. [ABSTRACT FROM AUTHOR]

The response of an ecosystem to perturbations is mediated by both antagonistic and facilitative interactions between spicies. It is thought that a community's resilience depends crucially on the food web-the network of trophic interactions-and on the food web's degree of compartmentalization. Despite its ecological importance, compartmentalization and the mechanisms that give rise to it remain poorly understood. Here we investigate several definitions of compartments, propose ways to understand the ecological meaning of these definitions, and quantify the degree of compartmentalization of empirical food webs. We find that the compartmentalization observed in empirical food webs can be accounted for solely by the niche organization of species and their diets. By uncovering connections between compartmentalizatioii and species' diet contiguity, our findings help us understand which perturbations can result in fragmentation of the food web and which can lead to catastrophic effects. Additionally, we show that the composition of compartments can be used to address the long-standing question of what determines the ecological niche of a species. [ABSTRACT FROM AUTHOR]

Taxa with smaller individuals tend to have shorter generation times and higher local abundance and diversity. The scaled specialization hypothesis (SSH) posits that taxocenes of smaller individuals should differentiate more rapidly and thoroughly along physiochemical gradients of a given age and extent. In a Panama rainforest, we evaluated how bacteria, fungi, and ants responded to two such gradients: one topographic and the other arising from nine years of NPK fertilization. Terminal restriction fragment length polymorphism (T-RFLP) delineated bacteria and fungi operational taxonomic units (OTUs); traditional taxonomy delineated the ants. Bacteria had higher local species richness than fungi and ants (averaging 48 vs. 30 vs. 6 OTUs in <0.25 m2). Bacteria OTUs were also more widely distributed (17% of OTUs were found on ⩾50% of sample plots compared to 3% for fungi and ants). Consistent with SSH, bacterial composition differed across short-term (+N and +P) and long-term (topographic) gradients; fungal taxocenes differed only along the long-term gradient; and ant taxocenes were homogenous across both. Body size can help predict community responses to a changing environment. [ABSTRACT FROM AUTHOR]

We propose a framework for hypothesis-testing of stable isotope ratios in ecological studies. Statistical procedures are based on analysis of nested linear models and a residual permutation procedure (RPP) that is employed to evaluate probabilities associated with test statistics. We used simulated examples and a real data set to illustrate the utility and generality of the method. First, we developed a test for differences in centroid location and dispersion of δ13C and δ15N values within and among groups of isotopic data. Second, we evaluated magnitude and direction of change in centroid position (termed "path") of a pair of isotopic samples separated in space/time relative to paths of other paired sample sets. Third, we compared attributes of path trajectories (size, direction, and shape) over sample sets containing more than two samples to provide a quantitative description of how patterns of isotopic ratios change in response to spatial and temporal gradients. Examples are limited to the bivariate case (δ13C-δ15N biplots), but the statistical method can readily be applied to univariate and multivariate cases. [ABSTRACT FROM AUTHOR]

The high levels of species diversity observed within many biological communities are captivating, yet the mechanisms that may maintain such diversity remain elusive. Many of the phenotypic differences observed among species cause interspecific trade-offs that ultimately act to maintain diversity through niche-based coexistence. In contrast, neutral community theory argues that phenotypic differences among species do not contribute to maintaining species diversity because species are ecologically equivalent. Here we provide experimental and observational field evidence that two phylogenetically very distant Enallagma species appear to be ecologically equivalent to one another. Experimental abundance manipulations showed that each species gains no demographic advantage at low relative abundance, whereas manipulations of total Enallagma abundance resulted in large increases in per capita mortality and large decreases in growth for both species. Moreover, demographic rates and relative abundances of multiple Enallagma species were uncorrelated with major environmental gradients in an observational study of 20 natural lakes. These are the expected patterns if species are ecologically equivalent. However, these results do not imply that all damselflies in these lakes are ecologically identical. Previous experimental results have demonstrated the operation of strong coexistence mechanisms maintaining Enallagma and its sister-genus Ischnura in these littoral food webs. Combined with a simple theoretical model we present, these results taken together show how both neutral and niche dynamics can jointly structure communities. [ABSTRACT FROM AUTHOR]

Mechanistic models of community assembly state that biotic and abiotic filters constrain species establishment through selection on their functional traits. Predicting this assembly process is hampered because few studies directly incorporate environmental measurements and scale up from species to community level and because the functional traits' significance is environment dependent. We analyzed community assembly by measuring structure, environmental conditions, and species traits of secondary forests in a species-rich tropical system. We found, as hypothesized, that community structure shaped the local environment and that strong relationships existed between this environment and the traits of the most successful species of the regeneration communities. Path and multivariate analyses showed that temperature and leaf traits that regulate it were the most important factors of community differentiation. Comparisons between the trait composition of the forest's regeneration, juvenile, and adult communities showed a consistent community assembly pattern. These results allowed us to identify the major functional traits and environmental factors involved in the assembly of dry-forest communities and demonstrate that environmental filtering is a predictable and fundamental process of community assembly, even in a complex system such as a tropical forest. [ABSTRACT FROM AUTHOR]

Abiotic, biotic, and dispersal constraints jointly control the spatial distributions of species, but few studies have directly evaluated how these forces interact and vary over time to create dynamic spatial distributions. Through three years of observation and two years of field manipulation, I investigated simultaneous constraints on the spatial distribution of Lupinus nanus, a native annual legume that grows in dense patches in California grasslands. I transplanted L. nanus across its own patch boundaries, yet within apparently suitable habitat, and assessed the demographic success of naturally occurring and seeded plants in plots with and without competitor removal in years that varied in temperature and rainfall. Core sites were defined as those consistently densely occupied, whereas peripheral sites were densely occupied only during some years, and exterior sites were consistently unoccupied or very sparsely occupied. Site types (core, periphery, and exterior) differed in soil moisture, P, and NO3. Competition limited emergence in all site types in the dry/warm year and in patch peripheries in the wet/cool year. Population fitness (seeds produced per seed added) was >1.0 in cores during all years. Peripheral sites had fitness near replacement in the wet/cool year, which was greatly increased by competition removal. Exterior fitness was <1.0 in both experimental years, regardless of seed addition and competitor removal. Seed addition did not increase site-specific fitness, and a seed bank was found to be present in all site types. Herbivory was greater in patch cores and peripheries than in exteriors. Soil variation exerted the most consistent control over patch limits, while competition played an intermittent role in excluding Lupinus from patch peripheries. The dynamic distribution of L. nanus is the product of temporal variation in specific abiotic and biotic niche axes, primarily soil characteristics and competition, rather than dispersal limitation. [ABSTRACT FROM AUTHOR]

Biotic interactions, such as competition and herbivory, can limit plant species ranges to a subset of edaphically suitable habitats, termed the realized niche. Here we explored the role that herbivores play in restricting the niche of serpentine ecotypes of the native California annual Collinsia sparsiflora. We planted seeds from four populations into a range of natural field environments that varied in the presence/absence of naturally occurring C. sparsiflora and in predicted suitability for growth and survival of the serpentine ecotype of C. sparsifIora. Path analysis was then used to model the direct and herbivore-mediated indirect effects of environmental variables on the survival of C. sparsiflora serpentine ecotypes. We found that C. sparsiflora received more herbivory when planted into areas where serpentine ecotypes of C. sparsifIora were not predicted to persist, and that increased herbivory was associated with decreased survival, suggesting that herbivores may limit the distribution of C. sparsiflora serpentine ecotypes. Additionally, we demonstrated that edaphic environmental variables impacted the survival of C. sparsiflora serpentine ecotypes both directly and indirectly, by altering interactions with herbivores. These indirect effects were probably trait-mediated and probably occurred because edaphic factors may influence plant traits that, in turn, alter attractiveness to herbivores. Although the magnitude of direct effects exceeded the magnitude of indirect effects, many strong herbivore-mediated indirect effects were detected. Thus, interactions between the abiotic environment and insect herbivory contributed to restricting the niche of C. sparsiflora serpentine ecotypes to a subset of available habitat. [ABSTRACT FROM AUTHOR]

Abiotic and biotic processes operate at multiple spatial and temporal scales to shape many ecological processes, including species distributions and demography. Current debate about the relative roles of niche-based and stochastic processes in shaping species distributions and community composition reflects, in part, the challenge of understanding how these processes interact across scales. Traditional statistical models that ignore autocorrelation and spatial hierarchies can result in misidentification of important ecological covariates. Here, we demonstrate the utility of a hierarchical modeling framework for testing hypotheses about the importance of abiotic factors at different spatial scales and local spatial autocorrelation for shaping species distributions and abundances. For the two orchid species studied, understory light availability and soil moisture helped to explain patterns of presence and abundance at a microsite scale (<4 m2), while soil organic content was important at a population scale (<400 m2). The inclusion of spatial autocorrelation is shown to alter the magnitude and certainty of estimated relationships between abundance and abiotic variables, and we suggest that such analysis be used more often to explore the relationships between species life histories and distributions. The hierarchical modeling framework is shown to have great potential for elucidating ecological relationships involving abiotic and biotic processes simultaneously at multiple scales. [ABSTRACT FROM AUTHOR]