Biology subjects

Terry, C.

Publications and source records attributed to Terry, C..

11 recordsLinked to original sources

bioRxiv2025

Unfeasible expectations: why simple predictors outperform structural stability measures for understanding community assembly

Understanding what determines community assembly and disassembly in a changing environment is a core challenge for ecology. Recently a family of structural stability approaches that determine the range of intrinsic growth rates compatible with system feasibility have been gaining popularity as a measure of how likely a community is able to persist in fluctuating conditions. This offers a theoretical basis for understanding and predicting the assembly and stability of complex multi-species communities from only interaction network structures. However, here I show that the high sensitivity of calculations of the feasibility domain, coupled with empirical uncertainties inherent in estimated interaction strength, are likely to preclude the approachs reliable application to empirical settings as a metric to compare the stability of different communities. Across four reanalyses of previous empirical demonstrations of the structural stability approach, more parsimonious measures based on species connectance provide better explanations for patterns of community assembly or differences in stability. Calculation of structural stability metrics therefore appears to lose, rather than synthesise, information embedded in empirical interaction matrices. This success of simpler measures is good news for the purposes of prediction and emphasises the value of multiple-competing hypotheses in validation tests to demonstrate value-added associated with new approaches.

ecology↗

bioRxiv2024

Transgenerational effects impact the vulnerability of a host-parasitoid system to rising temperatures.

O_LITransgenerational effects, non-evolutionary processes by which environmental conditions in one generation influence the performance in subsequent generations, are hypothesised to have substantial consequences for population dynamics under stochastic environments. However, any direct apparent detriment or advantage these processes generate for a focal species may be counteracted by concurrent effects upon interacting species. C_LIO_LIUsing an experimental Drosophila-parasitoid model system, we determined how the previous generations thermal environment impacts the thermal performance of both hosts and parasitoids. We found substantial responses in both trophic-levels, with potential evidence for both condition-transfer effects and adaptive transgenerational plasticity. C_LIO_LIWe used these results to parameterise discrete-time simulation models to explore how transgenerational effects of thermal conditions and temporal autocorrelation in temperature are expected to impact the time to extinction for this host-parasitoid system under climate change. The models predicted that transgenerational effects would significantly hasten the time to extinction, largely through a reduction in estimated average performance. Under the assumptions of one of the population dynamics models trialled, we identified an additional hastening of extinction from the combined effect of both host and parasitoid transgenerational effects. C_LIO_LIOur research demonstrates how community-level consequences of transgenerational effects may impact a populations sensitivity to climate change under a fluctuating environment and highlights the need to quantify and contextualise thermal transgenerational effects in their ecological setting. C_LI

ecology↗

bioRxiv2024

Experimental validation of ecological coexistence theory to forecast extinction under rising temperatures.

Interactions between species pose considerable challenges for forecasting the response of ecological communities to global changes. Coexistence theory could address this challenge by defining the conditions species can or cannot persist alongside competitors. However, although coexistence theory is increasingly deployed for projections, these frameworks have rarely been subjected to critical multigenerational validation tests. Here, using a highly replicated mesocosm experiment, I directly test if the modern coexistence theory approach can predict time-to-extirpation in the face of rising temperatures within the context of competition from a heat-tolerant species. Competition hastened expiration and the modelled point of coexistence breakdown overlapped with mean observations under both steady temperature increases and with additional environmental stochasticity. That said, although the theory identified the interactive effect between the stressors, predictive precision was low even in this simplified system. Nonetheless, these results support the careful use of coexistence modelling for forecasts and understanding drivers of change.

ecology↗

bioRxiv2022

Codistribution as an indicator of whole metacommunity response to environmental change.

Metacommunity structure can be summarised by fitting joint species distribution models and partitioning the variance explained into environmental, spatial and codistribution components. Here we identify how these components respond through time with directed environmental change and propose this as an indicator of sustained directional pressure. Through simulations, we identify how declines in the codistribution component can diagnose ecological breakdown, while rises in environmental and spatial components may indicate losses in peripheral areas and dispersal limitations. We test the method in two well-studied systems. Butterflies are known to be strongly responding to climate change, and we show that over 21 years the codistribution component declines for butterfly communities in southern England. By contrast, birds in the same region are under less climate pressure and, despite high occupancy turnover, show minimal change in metacommunity structure. The approach has high potential to summarise and compare the impact of external drivers on whole communities.

ecology↗

bioRxiv2022

Predicting Schrödinger's range-shifting cat: Analytic results for the impact of asymmetric environmental dependence on species responses to climate change

Analytic models for how species will respond to climate change can highlight key parameter dependencies. By mapping equations for population dynamics onto corresponding well-studied problems from quantum mechanics we derive analytical results for the frequently observed case of asymmetric environmental response curves. We derive expressions in terms of parameters representing climate velocity, dispersal rate, maximum growth rate, niche width, high-frequency climate variability and environmental performance curve skew for three key responses: 1) population persistence, 2) lag between range displacement and climate displacement, 3) location of maximum population sensitivity. Surprisingly, under our model assumptions, the direction of performance curve asymmetry does not strongly contribute to either persistence or lags. Conservation measures to support range-shifting populations may have most benefit near their environmental optimum or where the environmental dependence is shallow, irrespective of whether this is the leading or trailing edge. A metapopulation simulation corroborates our results.

ecology↗

bioRxiv2021

Temporally robust spatial structure in ecosystems explained by local biodiversity regulation

The mechanisms determining the distribution of the number of sites species occupy--the occupancy frequency distribution (OFD)--remain incompletely understood despite decades of research. Here we study OFD in fresh-water metacommunities in England. We show that OFD are largely time invariant despite continuous turnover in community composition and well described by log-series distributions. Both shape and temporal robustness are readily explained by a simple patch occupancy model with intrinsic regulation of local richness. The model is mathematically analogous to classical neutral theory, but concerns numbers of patches occupied instead of individuals present. The precise shape of the models log-series OFD is determined by a parameter representing the rate of colonisation from adjacent sites, which we estimate for the data. Our results support the view that meta-community structure reflects a dynamic steady state controlled by local ecological constraints. Interspecific trait differences underlie these constraints, but are unlikely to determine macroecological structure.

ecology↗

bioRxiv2021

Predictors of the long-term conservation value of sites in a mechanistic metacommunity model

Conserving biodiversity often requires deciding which sites to prioritise for protection. Predicting the impact of habitat loss is a major challenge, however, since impacts can be distant from the perturbation in both space and time. Here we study the long-term impacts of habitat loss in a mechanistic metacommunity model in terms of both immediate extinctions and secondary species losses. We find that biomass-at-site, closely related to site area, is a poor predictor of long-term regional species losses following site removal. Knowledge of the compositional distinctness (average between-site Bray-Curtis dissimilarity) of the removed community can markedly improve the prediction of impacts at the regional scale, even when biotic responses play out at substantial spatial or temporal distance from the removed site. Fitting our model to empirical species-by-site tables describing Andean diatoms and Brazilian lichen-fungi, we show that compositional distinctness surpasses area as a predictor of long-term species losses in the empirically relevant parameter range. Our results robustly demonstrate that site area alone is not sufficient to gauge conservation priorities; analysis of compositional distinctness permits improved prioritisation at low cost.

ecology↗

bioRxiv2021

No pervasive size trend in global community dynamics.

While recent meta-analyses have suggested that local taxonomic richness has on average remained invariant, potential shifts in functional traits remain underexplored at global scales. Here, by linking the largest cross-taxa community time series database to multiple trait databases, we show that within communities there is no clear trend between size traits and changes in abundance rank over time. This suggests that there is no pervasive tendency across biomes for larger species to be doing proportionally better or worse than smaller species.

ecology↗

bioRxiv2021

Synthesising the multiple impacts of climatic variability on community responses to climate change

Recent developments in understanding and predicting species responses to climate change have emphasised the importance of both environmental variability and consideration of the wider biotic community. However, to date, the interaction between the two has received less attention. Both theoretical and empirical results suggest that the combined effect of environmental variability and interspecific interactions can have strong impacts on existing range limits. Here we explore how competitive interactions and temporal variability can interact with the potential to strongly influence range shift dynamics. We highlight the need to understand these between-process interactions in order to predict how species will respond to global change. In particular, future research will need to move from evaluating possibilities to quantifying their impact. We emphasise the value and utility of empirically parameterised models to determine the direction and relative importance of these forces in natural systems.

ecology↗

bioRxiv2020

The effect of natural enemies on the coexistence of competing species - an empirical test using Bayesian modern coexistence theory

O_LIThe role of natural enemies in promoting coexistence of competing species has generated substantial debate. Modern coexistence theory provides a detailed framework to investigate this topic, but there have been remarkably few empirical applications to the impact of natural enemies. C_LIO_LIWe tested experimentally the capacity for a generalist enemy to promote coexistence of competing insect species, and the extent to which any impact can be predicted by trade-offs between reproductive rate and susceptibility to natural enemies. C_LIO_LIWe used experimental mesocosms to conduct a fully-factorial pairwise competition experiment for six rainforest Drosophila species, with and without a generalist pupal parasitoid. We then parameterised models of competition and examined the coexistence of each pair of Drosophila species within the framework of modern coexistence theory. C_LIO_LIWe found idiosyncratic impacts of parasitism on pairwise coexistence, mediated through changes in fitness differences, not niche differences. There was no evidence of an overall reproductive rate - susceptibility trade-off. Pairwise reproductive rate - susceptibility relationships were not useful shortcuts for predicting the impact of parasitism on coexistence. C_LIO_LIOur results exemplify the value of modern coexistence theory in multi-trophic contexts and the importance of contextualising the impact of natural enemies. In the set of species investigated, competition was affected by the higher trophic level, but the overall impact on coexistence cannot be easily predicted just from knowledge of relative susceptibility. Methodologically, our Bayesian approach highlights issues with the separability of model parameters within modern coexistence theory and shows how using the full posterior parameter distribution improves inferences. This method should be widely applicable for understanding species coexistence in a range of systems. C_LI

ecology↗

bioRxiv2017

Identifying Important Interaction Modifications in Ecological Systems

Trophic interaction modifications, where a consumer-resource link is affected by additional species, are widespread and significant causes of indirect effects in ecological networks. The sheer number of potential interaction modifications in ecological systems poses a considerable challenge, making prioritisation for empirical study essential. Here, we introduce measures to quantify the topological relationship of individual interaction modifications relative to the underlying network. We use these, together with measures for the strength of trophic interaction modifications to identify modifications that are most likely to exert significant effects on the dynamics of whole systems. Using a set of simulated food webs and randomly distributed interaction modifications, we test whether a subset of interaction modifications important for the local stability and direction of species responses to perturbation of complex networks can be identified. We show that trophic interaction modifications affecting interactions with a high biomass flux, those that connect species otherwise distantly linked, and those where high trophic-level species modify to interactions lower in the web have particular importance for dynamics. In contrast, the centrality of modifications in the network provided little information. This work demonstrates that analyses of interaction modifications can be tractable at the network scale and highlights the importance of understanding the relationship between the distributions of trophic and non-trophic effects.

ecology↗