Biology subjects

Dinner O'Sullivan, J. L.

Publications and source records attributed to Dinner O'Sullivan, J. L..

7 recordsLinked to original sources

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

Intrinsic ecological dynamics drive biodiversity turnover in model metacommunities

Turnover of species composition through time is frequently observed in ecosystems. It is often interpreted as indicating the impact of changes in the environment. Continuous turnover due solely to ecological dynamics--species interactions and dispersal--is also known to be theoretically possible, however the prevalence of such autonomous turnover in natural communities remains unclear. Here we demonstrate that observed patterns of compositional turnover and other important macroecological phenomena can be reproduced in large spatially explicit model ecosystems, without external forcing such as environmental change or the invasion of new species into the model. These results imply that the potential role of autonomous turnover as a widespread and important natural process is underappreciated, challenging assumptions implicit in many observation and management tools. Quantifying the baseline level of compositional change would greatly improve ecological status assessments. One Sentence SummaryBiodiversity change previously attributed to external drivers is explainable as resulting from intrinsic ecosystem dynamics.

ecology↗

bioRxiv2018

Metacommunity-scale biodiversity regulation and the self-organized emergence of macroecological patterns

There exist a number of key macroecological patterns whose ubiquity suggests the spatio-temporal structure of ecological communities is governed by some universal mechanisms. The nature of these mechanisms, however, remains poorly understood. Here we probe spatio-temporal patterns species richness and community composition using a simple metacommunity assembly model. Despite making no a priori assumptions regarding biotic spatial structure or the distribution of biomass across species, model metacommunities self-organize to reproduce well documented patterns including characteristic species abundance distributions, range size distributions and species area relations. Also in agreement with observations, species richness in our model attains an equilibrium despite continuous species turnover. Crucially, it is in the neighbourhood of the equilibrium that we observe the emergence of these key macroecological patterns. Biodiversity equilibria in models occur due to the onset of ecological structural instability, a population-dynamical mechanism. This strongly suggests a causal link between local community processes and macroecological phenomena.

ecology↗