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1. Extreme site fidelity as an optimal strategy in an unpredictable and homogeneous environment

   https://doi.org/10.1111/1365-2435.13390  

   Gerber, Brian D. ; Hooten, Mevin B. ; Peck, Christopher P. ; Rice, Mindy B. ; Gammonley, James H. ; Apa, Anthony D. ; Davis, Amy J. ; Lemaître, ed., Jean‐François ( July 2019 , Functional Ecology)

   Animal site fidelity structures space use, population demography and ultimately gene flow. Understanding the adaptive selection for site fidelity patterns provides a mechanistic understanding to both spatial and population processes. This can be achieved by linking space use with environmental variability (spatial and temporal) and demographic parameters. However, rarely is the environmental context that drives the selection for site fidelity behaviour fully considered.

   We use ecological theory to understand whether the spatial and temporal variability in breeding site quality can explain the site fidelity behaviour and demographic patterns of Gunnison sage‐grouse (Centrocercus minimus). We examined female site fidelity patterns across multiple spatial scales: proximity of consecutive year nest locations, space‐use overlap within and across the breeding and brooding seasons, and fidelity to a breeding patch. We also examined the spatial and temporal variability in nest, chick, juvenile and adult survival.

   We found Gunnison sage‐grouse to be site faithful to their breeding patch, area of use within the patch and generally where they nest, suggesting an “Always Stay” site fidelity strategy. This is an optimal evolutionary strategy when site quality is unpredictable. Further, we found limited spatial variability in survival within age groups, suggesting little demographic benefit to moving among patches. We suggest Gunnison sage‐grouse site fidelity is driven by the unpredictability of predation in a relatively homogeneous environment, the lack of benefits and likely costs to moving across landscape patches and leaving known lek and breeding/brooding areas.

   Space use and demography are commonly studied separately. More so, site fidelity patterns are rarely framed in the context of ecological theory, beyond questions related to the win‐stay:lose‐switch rule. To move beyond describing patterns and understand the adaptive selection driving species movements and their demographic consequences require integrating movement, demography and environmental variability in a synthetic framework.

   Site fidelity theory provides a coherent framework to simultaneously investigate the spatial and population ecology of animal populations. Using it to frame ecological questions will lead to a more mechanistic understanding of animal movement, spatial population structuring and meta‐population dynamics.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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2. Demographic back‐casting reveals that subtle dimensions of climate change have strong effects on population viability

   https://doi.org/10.1111/1365-2745.13471  

   Czachura, Kevin ; Miller, Tom E. X. ; Salguero‐Gómez, ed., Roberto ( August 2020 , Journal of Ecology)

   The effects of climate change on population viability reflect the net influence of potentially diverse responses of individual‐level demographic processes (growth, survival, regeneration) to multiple components of climate. Articulating climate–demography connections can facilitate forecasts of responses to future climate change as well as back‐casts that may reveal how populations responded to historical climate change.

   We studied climate–demography relationships in the cactusCyclindriopuntia imbricata; previous work indicated that our focal population has high abundance but a negative population growth rate, where deaths exceed births, suggesting that it persists under extinction debt. We parameterized a climate‐dependent integral projection model with data from a 14‐year field study, then back‐casted expected population growth rates since 1900 to test the hypothesis that recent climate change has driven this population into extinction debt.

   We found clear patterns of climate change in our central New Mexico study region but, contrary to our hypothesis,C. imbricatahas most likely benefitted from recent climate change and is on track to reach replacement‐level population growth within 37 years, or sooner if climate change accelerates. Furthermore, the strongest feature of climate change (a trend towards years that are overall warmer and drier, captured by the first principal component of inter‐annual variation) was not the main driver of population responses. Instead, temporal trends in population growth were dominated by more subtle, seasonal climatic factors with relatively weak signals of recent change (wetter and milder cool seasons, captured by the second and third principal components).

   Synthesis. Our results highlight the challenges of back‐casting or forecasting population dynamics under climate change, since the most apparent features of climate change may not be the most important drivers of ecological responses. Environmentally explicit demographic models can help meet this challenge, but they must consider the magnitudes of different aspects of climate change alongside the magnitudes of demographic responses to those changes.

    

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3. Effects of range and niche position on the population dynamics of a tropical plant

   https://doi.org/10.1002/ecy.3990  

   Moutouama, Jacob K. ; Gaoue, Orou G. ( February 2023 , Ecology)

   The center‐periphery hypothesis predicts a decline in population performance toward the periphery of a species' range, reflecting an alteration of environmental conditions at range periphery. However, the rare demographic tests of this hypothesis failed to disentangle the role of geography from that of ecological niche and are biased toward temperate regions. We hypothesized that, because species are expected to experience optimal abiotic conditions at their climatic niche center, (1) central populations will have better demographic growth, survival, and fertility than peripheral populations. As a result, (2) central populations are expected to have higher growth rates than peripheral populations. Peripheral populations are expected to decline, thus limiting species range expansion beyond these boundaries. Because peripheral populations are expected to be in harsh environmental conditions, (3) population growth rate will be more sensitive to perturbation of survival‐growth rather than fertility in peripheral populations. Finally, we hypothesized that (4) soils properties will drive the variations in population growth rates for narrowly distributed species for which small scale ecological factors could outweigh landscape level drivers. To test these hypotheses, we studied the demography ofThunbergia atacorensis(Acanthaceae), a range‐limited herb in West Africa. We collected three years of demographic data to parameterize an integral projection model (IPM) and estimated population level demographic statistics. Demographic vital rates and population growth rates did not change significantly with distance from geographic or climatic center, contrary to predictions. However, populations at the center of the geographic range were demographically more resilient to perturbation than those at the periphery. Soil nitrogen was the main driver of population growth rate variation. The relative influence of survival‐growth on population growth rates exceeded that of fertility at the geographic range center while we observed the opposite pattern for climatic niche. Our study highlights the importance of local scale processes in shaping the dynamics and distribution of range‐limited species. Our findings also suggest that the distinction between geographic distribution and climatic niche is important for a robust demographic test of the center‐periphery hypothesis.

    

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4. Climate‐mediated population dynamics of a migratory songbird differ between the trailing edge and range core

   https://doi.org/10.1002/ecm.1559  

   Lewis, William B. ; Cooper, Robert J. ; Chandler, Richard B. ; Chitwood, Ryan W. ; Cline, Mason H. ; Hallworth, Michael T. ; Hatt, Joanna L. ; Hepinstall‐Cymerman, Jeff ; Kaiser, Sara A. ; Rodenhouse, Nicholas L. ; et al ( January 2023 , Ecological Monographs)

   Understanding the demographic drivers of range contractions is important for predicting species' responses to climate change; however, few studies have examined the effects of climate change on survival and recruitment across species' ranges. We show that climate change can drive trailing edge range contractions through the effects on apparent survival, and potentially recruitment, in a migratory songbird. We assessed the demographic drivers of trailing edge range contractions using a long‐term demography dataset for the black‐throated blue warbler (Setophaga caerulescens) collected across elevational climate gradients at the trailing edge and core of the breeding range. We used a Bayesian hierarchical model to estimate the effect of climate change on apparent survival and recruitment and to forecast population viability at study plots through 2040. The trailing edge population at the low‐elevation plot became locally extinct by 2017. The local population at the mid‐elevation plot at the trailing edge gradually declined and is predicted to become extirpated by 2040. Population declines were associated with warming temperatures at the mid‐elevation plot, although results were more equivocal at the low‐elevation plot where we had fewer years of data. Population density was stable or increasing at the range core, although warming temperatures are predicted to cause population declines by 2040 at the low‐elevation plot. This result suggests that even populations within the geographic core of the range are vulnerable to climate change. The demographic drivers of local population declines varied between study plots, but warming temperatures were frequently associated with declining rates of population growth and apparent survival. Declining apparent survival in our study system is likely to be associated with increased adult emigration away from poor‐quality habitats. Our results suggest that demographic responses to warming temperatures are complex and dependent on local conditions and geographic range position, but spatial variation in population declines is consistent with the climate‐mediated range shift hypothesis. Local populations of black‐throated blue warblers near the warm‐edge range boundary at low latitudes and low elevations are likely to be the most vulnerable to climate change, potentially leading to local extirpation and range contractions.

    

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5. Species‐specific variation in germination rates contributes to spatial coexistence more than adult plant water use in four closely related annual flowering plants

   https://doi.org/10.1111/1365-2745.13408  

   James, Aubrie R. M. ; Burnette, Timothy E. ; Mack, Jasmine ; James, David E. ; Eckhart, Vincent M. ; Geber, Monica A. ; Zhou, ed., Shurong ( May 2020 , Journal of Ecology)

   Spatial partitioning is a classic hypothesis to explain plant species coexistence, but evidence linking local environmental variation to spatial sorting, demography and species' traits is sparse. If co‐occurring species' performance is optimized differently along environmental gradients because of trait variation, then spatial variation might facilitate coexistence.

   We used a system of four naturally co‐occurring species ofClarkia(Onagraceae) to ask whether distribution patchiness corresponds to variation in two environmental variables that contribute to hydrological variation. We then reciprocally sowedClarkiainto each patch type and measured demographic rates in the absence of congeneric competition. Species sorted in patches along one or both gradients, and in three of the four species, germination rate in the ‘home’ patch was higher than all other patches.

   Spatially variable germination resulted in the same three species exhibiting the highest population growth rates in their home patches.

   Species' trait values related to plant water use, as well as indicators of water stress in home patches, differed among species and corresponded to home patch attributes. However, post‐germination survival did not vary among species or between patch types, and fecundity did not vary spatially.

   Synthesis. Our research demonstrates the likelihood that within‐community spatial heterogeneity affects plant species coexistence, and presents novel evidence that differential performance in space is explained by what happens in the germination stage. Despite the seemingly obvious link between adult plant water‐use and variation in the environment, our results distinguish the germination stage as important for spatially variable population performance.

    

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