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Population cycles have been observed in mammals as well as insects, but consistent population cycling has rarely been documented in agroecosystems and never for a beetle. We analysed the long-term population patterns of the cabbage stem flea beetle Psylliodes chrysocephala in winter oilseed rape over 50 years. Psylliodes chrysocephala larval density from 3045 winter oilseed rape fields in southern Sweden showed strong 8-year population cycles in regional mean density. Fluctuations in larval density were synchronous over time across five subregional populations. Subregional mean environmental variables explained 90.6% of the synchrony in P. chrysocephala populations at the 7-11 year time-scale. The number of days below -10°C showed strong anti-phase coherence with larval densities in the 7-11 year time-scale, such that more cold days resulted in low larval densities. High levels of the North Atlantic Oscillation weather system are coherent and anti-phase with cold weather in Scania, Sweden. At the field-scale, later crop planting date and more cold winter days were associated with decreased overwintering larval density. Warmer autumn temperatures, resulting in greater larval accumulated degree days early in the season, increased overwintering larval density. Despite variation in environmental conditions and crop management, 8-year cycles persisted for cabbage stem flea beetle throughout the 50 years of data collection. Moran effects, influenced by the North Atlantic Oscillation weather patterns, are the primary drivers of this cycle and synchronicity. Insect pest data collected in commercial agriculture fields is an abundant source of long-term data. We show that an agricultural pest can have the same periodic population cycles observed in perennial and unmanaged ecosystems. This unexpected finding has implications for sustainable pest management in agriculture and shows the value of long-term pest monitoring projects as an additional source of time-series data to untangle the drivers of population cycles., (© 2022 The Authors. Journal of Animal Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society.)

Clarifying the effects of biodiversity on ecosystem stability in the context of global environmental change is crucial for maintaining ecosystem functions and services. Asynchronous changes between trophic levels over time (i.e. trophic community asynchrony) are expected to increase trophic mismatch and alter trophic interactions, which may consequently alter ecosystem stability. However, previous studies have often highlighted the stabilising mechanism of population asynchrony within a single trophic level, while rarely examining the mechanism of trophic community asynchrony between consumers and their food resources. In this study, we analysed the effects of population asynchrony within and between trophic levels on community stability under the disturbances of climate warming, fishery decline and de-eutrophication, based on an 18-year monthly monitoring dataset of 137 phytoplankton and 91 zooplankton in a subtropical lake. Our results showed that species diversity promoted community stability mainly by increasing population asynchrony both for phytoplankton and zooplankton. Trophic community asynchrony had a significant negative effect on zooplankton community stability rather than that of phytoplankton, which supports the match-mismatch hypothesis that trophic mismatch has negative effects on consumers. Furthermore, the results of the structural equation models showed that warming and top-down effects may simultaneously alter community stability through population dynamics processes within and between trophic levels, whereas nutrients act on community stability mainly through the processes within trophic levels. Moreover, we found that rising water temperature decreased trophic community asynchrony, which may challenge the prevailing idea that climate warming increases the trophic mismatch between primary producers and consumers. Overall, our study provides the first evidence that population and trophic community asynchrony have contrasting effects on consumer community stability, which offers a valuable insight for addressing global environmental change., (© 2024 The Author(s). Journal of Animal Ecology © 2024 British Ecological Society.)

Disentangling empirically the many processes affecting spatial population synchrony is a challenge in population ecology. Two processes that could have major effects on the spatial synchrony of wild population dynamics are density dependence and variation in environmental conditions like temperature. Understanding these effects is crucial for predicting the effects of climate change on local and regional population dynamics.We quantified the direct contribution of local temperature and density dependence to spatial synchrony in the population dynamics of nine fish species inhabiting the Barents Sea. First, we estimated the degree to which the annual spatial autocorrelations in density are influenced by temperature. Second, we estimated and mapped the local effects of temperature and strength of density dependence on annual changes in density. Finally, we measured the relative effects of temperature and density dependence on the spatial synchrony in changes in density.Temperature influenced the annual spatial autocorrelation in density more in species with greater affinities to the benthos and to warmer waters. Temperature correlated positively with changes in density in the eastern Barents Sea for most species. Temperature had a weak synchronizing effect on density dynamics, while increasing strength of density dependence consistently desynchronised the dynamics.Quantifying the relative effects of different processes affecting population synchrony is important to better predict how population dynamics might change when environmental conditions change. Here, high degrees of spatial synchrony in the population dynamics remained unexplained by local temperature and density dependence, confirming the presence of additional synchronizing drivers, such as trophic interactions or harvesting. [ABSTRACT FROM AUTHOR]

Food webs depict the tangled web of trophic interactions associated with the functioning of an ecosystem. Understanding the mechanisms providing stability to these food webs is therefore vital for conservation efforts and the management of natural systems. Here, we first characterised a tropical stream meta-food web and five individual food webs using a Bayesian Hierarchical approach unifying three sources of information (gut content analysis, literature compilation and stable isotope data). With data on population-level biomass and individually measured body mass, we applied a bioenergetic model and assessed food web stability using a Lotka-Volterra system of equations. We then assessed the resilience of the system to individual species extinctions using simulations and investigated the network patterns associated with systems with higher stability. The model resulted in a stable meta-food web with 307 links among the 61 components. At the regional scale, 70% of the total energy flow occurred through a set of 10 taxa with large variation in body masses. The remaining 30% of total energy flow relied on 48 different taxa, supporting a significant dependency on a diverse community. The meta-food web was stable against individual species extinctions, with a higher resilience in food webs harbouring omnivorous fish species able to connect multiple food web compartments via weak, non-specialised interactions. Moreover, these fish species contributed largely to the spatial variation among individual food webs, suggesting that these species could operate as mobile predators connecting different streams and stabilising variability at the regional scale. Our results outline two key mechanisms of food web stability operating in tropical streams: (i) the diversity of species and body masses buffering against random and size-dependent disturbances and (ii) high regional diversity and weak omnivorous interactions of predators buffering against local stochastic variation in species composition. These mechanisms rely on high local and regional biodiversity in tropical streams, which is known to be strongly affected by human impacts. Therefore, an urgent challenge is to understand how the ongoing systematic loss of diversity jeopardises the stability of stream food webs in human-impacted landscapes., (© 2024 The Author(s). Journal of Animal Ecology © 2024 British Ecological Society.)

As air temperature increases, it has been suggested that smaller individual body size may be a general response to climate warming. However, for ectotherms inhabiting cold, highly seasonal environments, warming temperatures may increase the scope for growth and result in larger body size.In a long‐term study of individual brook trout Salvelinus fontinalis and brown trout Salmo trutta inhabiting a small stream network, individual lengths increased over the course of 15 years. As size‐selective gains and losses to the population acted to reduce body sizes and mean body size at first tagging in the autumn (<60 mm) were not observed to change substantially over time, the increase in body size was best explained by higher individual growth rates.For brook trout, increasing water temperatures during the spring (when both trout species accomplish most of their total annual growth) was the primary driver of growth rate for juvenile fish and the environmental factor which best explained increases in individual body size over time.For brown trout, by contrast, reduction in and subsequent elimination of juvenile Atlantic salmon Salmo salar midway through the study period explained most of the increases in juvenile growth and body size.In addition to these major trends, a considerable amount of interannual variation in trout growth and body size was explained by other abiotic (stream flow) and biotic (population density) factors with the direction and magnitude of these effects differing by season, age‐class and species. For example, stream flow was the dominant growth rate driver for adult fish with strong positive effects in the summer and autumn, but flow variation could not explain increases in body size as we observed no trend in flow.Overall, our work supports the general contention that for high‐latitude ectotherms, increasing spring temperatures associated with a warming climate can result in increased growth and individual body size (up to a point), but context‐dependent change in other factors can substantially contribute to both interannual variation and longer‐term effects. [ABSTRACT FROM AUTHOR]

Identifying the drivers of population fluctuations in spatially distinct populations remains a significant challenge for ecologists. Whereas regional climatic factors may generate population synchrony (i.e. the Moran effect), local factors including the level of density dependence may reduce the level of synchrony. Although divergences in the scaling of population synchrony and spatial environmental variation have been observed, the regulatory factors that underlie such mismatches are poorly understood.Few previous studies have investigated how density‐dependent processes and population‐specific responses to weather variation influence spatial synchrony at both local and regional scales. We addressed this issue in a pond‐breeding amphibian, the great crested newt Triturus cristatus. We used capture–recapture data collected through long‐term surveys in five T. cristatus populations in Western Europe.In all populations—and subpopulations within metapopulations—population size, annual survival and recruitment fluctuated over time. Likewise, there was considerable variation in these demographic rates between populations and within metapopulations. These fluctuations and variations appear to be context‐dependent and more related to site‐specific characteristics than local or regional climatic drivers. We found a low level of demographic synchrony at both local and regional levels. Weather has weak and spatially variable effects on survival, recruitment and population growth rate. In contrast, density dependence was a common phenomenon (at least for population growth) in almost all populations and subpopulations.Our findings support the idea that the Moran effect is low in species where the population dynamics more closely depends on local factors (e.g. population density and habitat characteristics) than on large‐scale environmental fluctuation (e.g. regional climatic variation). Such responses may have far‐reaching consequences for the long‐term viability of spatially structured populations and their ability to respond to large‐scale climatic anomalies. [ABSTRACT FROM AUTHOR]

Spatial synchrony in population dynamics can be caused by dispersal or spatially correlated variation in environmental factors like weather (Moran effect). Distinguishing between these mechanisms is challenging for natural populations, and the study of dispersal‐induced synchrony in particular has been dominated by theoretical modelling and laboratory experiments.The goal of the present study was to evaluate the evidence for dispersal as a cause of meso‐scale (distances of tens of kilometres) spatial synchrony in natural populations of the two cyclic geometrid moths Epirrita autumnata and Operophtera brumata in sub‐arctic mountain birch forest in northern Norway.To infer the role of dispersal in geometrid synchrony, we applied three complementary approaches, namely estimating the effect of design‐based dispersal barriers (open sea) on synchrony, comparing the strength of synchrony between E. autumnata (winged adults) and the less dispersive O. brumata (wingless adult females), and relating the directionality (anisotropy) of synchrony to the predominant wind directions during spring, when geometrid larvae engage in windborne dispersal (ballooning).The estimated effect of dispersal barriers on synchrony was almost three times stronger for the less dispersive O. brumata than E. autumnata. Inter‐site synchrony was also weakest for O. brumata at all spatial lags. Both observations argue for adult dispersal as an important synchronizing mechanism at the spatial scales considered. Further, synchrony in both moth species showed distinct anisotropy and was most spatially extensive parallel to the east–west axis, coinciding closely to the overall dominant wind direction. This argues for a synchronizing effect of windborne larval dispersal. Congruent with most extensive dispersal along the east–west axis, E. autumnata also showed evidence for a travelling wave moving southwards at a speed of 50–80 km/year.Our results suggest that dispersal processes can leave clear signatures in both the strength and directionality of synchrony in field populations, and highlight wind‐driven dispersal as promising avenue for further research on spatial synchrony in natural insect populations. [ABSTRACT FROM AUTHOR]

A shift in the relative arrival of offspring, for example a shift in hatching time, can affect competition at the intraspecific level through size‐mediated priority effects, where the larger individuals gain more resources. These priority effects are likely to be affected by climate warming and the rate of intraspecific predation, that is cannibalism.In a laboratory experiment, we examined size‐mediated priority effects in larvae of the univoltine damselfly, Lestes sponsa, at two different temperatures (21 and 23°C). We created three size groups of larvae by manipulating hatching time: early hatched with a large size (extra‐advanced), intermediate hatched with an intermediate size (advanced) and late hatched with a small size (non‐advanced). Thereafter, we reared the larvae from these groups in non‐mixed and mixed groups of 12 larvae.We found strong priority and temperature effects. First, extra‐advanced larvae most often had higher survival, growth and development rates than non‐advanced larvae in mixed groups, compared to groups that consisted of only extra‐advanced larvae. Second, temperature increased growth and development rates and cannibalism.However, the strength of priority effects did not differ between the two experimental temperatures, because there was no statistical interaction between temperature and treatments. That is, the mixed and non‐mixed groups of non‐advanced, advanced and extra‐advanced larvae showed the same relative change in life‐history traits across the two temperatures.Non‐advanced and advanced larvae had similar or higher growth rate and mass in mixed groups compared to non‐mixed groups, suggesting that predation from advanced larvae in the mixed group released resources for the non‐advanced and advanced larvae that survived despite cannibalism risk. Thus, a thinning effect occurred due to cannibalism caused by priority effects.The results suggest that a shift in the relative arrival of offspring can cause temperature‐dependent priority effects, mediated through cannibalism, growth and development, which may change the size distribution and abundance of emerging aquatic insects. Shifts in the relative hatching of offspring can lead size‐mediated priority effects. This study shows that such priority effects have a twofold advantage in early‐hatching individuals: higher growth and higher cannibalism on early‐hatching individuals. In addition, a two‐degree higher temperature increased growth and cannibalism. [ABSTRACT FROM AUTHOR]

The spatial configuration and size of patches influence metapopulation dynamics by altering colonisation–extinction dynamics and local density dependency. This spatial forcing as determined by the metapopulation typology then imposes strong selection pressures on life‐history traits, which will in turn feed back on the ecological metapopulation dynamics. Given the relevance of metapopulation persistence for biological conservation, and the potential rescuing role of evolution, a firm understanding of the relevance of these eco‐evolutionary processes is essential.We here follow a systems' modelling approach to quantify the importance of spatial forcing and experimentally observed life‐history evolution for metapopulation demography as quantified by (meta)population size and variability. We therefore developed an individual‐based model matching an earlier experimental evolution with spider mites to perform virtual translocation and invasion experiments that would have been otherwise impossible to conduct.We show that (a) metapopulation demography is more affected by spatial forcing than by life‐history evolution, but that life‐history evolution contributes substantially to changes in local‐ and especially metapopulation‐level population sizes, (b) extinction rates are minimised by evolution in classical metapopulations, and (c) evolution is optimising individual performance in metapopulations when considering the importance of more cryptic stress resistance evolution.Ecological systems' modelling opens up a promising avenue to quantify the importance of eco‐evolutionary feedbacks in spatially structured populations. Metapopulation sizes are especially impacted by evolution, but its variability is mainly determined by the spatial forcing.Eco‐evolutionary dynamics can increase the persistence of classical metapopulations. Conservation of genetic variation and, hence, adaptive potential is thus not only essential in the face of environmental change; it also generates putative rescuing feedbacks that impact metapopulation persistence. In this paper, the authors follow a system's modelling approach to disentangle the role of metapopulation structure relative to evolution for metapopulation performance. They provide evidence that metapopulation‐level selection maximises individual performance and, more importantly, that evolved changes in life histories following changes in metapopulation structure have the potential to feed back on metapopulation dynamics, especially on local and metapopulation sizes. [ABSTRACT FROM AUTHOR]

Spatially separated populations of the same species often exhibit correlated fluctuations in abundance, a phenomenon known as spatial synchrony. Dispersal can generate spatial synchrony. In nature, most individuals disperse short distances with a minority dispersing long distances. The effect of occasional long distance dispersal on synchrony is untested, and theoretical predictions are contradictory. Occasional long distance dispersal might either increase both overall synchrony and the spatial scale of synchrony, or reduce them.We conducted a protist microcosm experiment to test whether occasional long distance dispersal increases or decreases overall synchrony and the spatial scale of synchrony.We assembled replicate 15‐patch ring metapopulations of the protist predator Euplotes patella and its protist prey Tetrahymena pyriformis. All metapopulations experienced the same dispersal rate, but differed in dispersal distance. Some metapopulations experienced strictly short distance (nearest neighbour) dispersal, others experienced a mixture of short‐ and long distance dispersal.Occasional long distance dispersal increased overall spatial synchrony and the spatial scale of synchrony for both prey and predators, though the effects were not statistically significant for predators. As predicted by theory, dispersal generated spatial synchrony by entraining the phases of the predator–prey cycles in different patches, a phenomenon known as phase locking.Our results are consistent with theoretical models predicting that occasional long distance dispersal increases spatial synchrony. However, our results also illustrate that the spatial scale of synchrony need not match the spatial scale of the processes generating synchrony. Even strictly short distance dispersal maintained high spatial synchrony for many generations at spatial scales much longer than the dispersal distance, thanks to phase locking. The authors show experimentally that even occasional long distance dispersal can synchronize population cycles on large spatial scales. This helps explain why population cycles in nature often are synchronized over distances much longer than the typical dispersal distance. Pictured is the main study organism, the ciliate protist Euplotes patella (photo by Jeremy Fox). [ABSTRACT FROM AUTHOR]