Biology subjects

Gellner, G.

Publications and source records attributed to Gellner, G..

3 recordsLinked to original sources

bioRxiv2023

Can higher-order interactions resolve the species coexistence paradox?

Most ecological models are based on the assumption that species interact in pairs. Emerging in diverse communities, however, are higher-order interactions, in which two or more species jointly impact the growth of a third species. A pitfall of the pairwise approach is that it misses the higher-order interactions potentially responsible for maintaining diversity in nature. Here, we explore how well higher-order interactions enable coexistence when pairwise interactions are insufficient to do so. Specifically, we explore the stability properties of systems where higher-order interactions guarantee that a specified set of abundances are a feasible equilibrium of the dynamics. Even these higher-order interactions do not necessarily produce robust coexistence. We find that facilitative higher-order interactions that counter pairwise competitive interactions are less likely to generate stable equilibria than competitive interactions countering pairwise facilitation. In both cases the system is more likely to be stable when the pairwise interactions are weak, and when the equilibrium abundances are near those produced by the pairwise interactions. Last, we show that correlations between the pairwise and higher-order interactions permit robust coexistence in diverse systems. Our work reveals the challenges in generating stable coexistence through higher-order interactions, but also uncovers higher-order interaction patterns that can enable diversity.

ecology↗

bioRxiv2022

Slower organisms exhibit sudden population disappearances in a reddened world

Nature is replete with variation in the body sizes, reproductive output, and generation times of species that produce life history responses known to vary from small and fast to large and slow. Although researchers recognize that life history speed likely dictates fundamental processes in consumer-resource interactions like productivity and stability, theoretical work remains incomplete in this critical area. Here, we examine the role of life history speed on consumer-resource interactions by using a well used mathematical approach that manipulates the speed of the consumers growth rate in a consumer-resource interaction. Importantly, this approach holds the isocline geometry intact allowing us to assess the impacts of altered life history speed on stability (coefficient of variation, CV) without changing the underlying qualitative dynamics. Although slowing life history can be initially stabilizing, we find that in stochastic settings slowing ultimately drives highly destabilizing population disappearances, especially under reddened noise. Our results suggest that human-driven reddening of noise may decrease species stability because the autocorrelation of red noise enlarges the period and magnitude of perturbations, overwhelming a species natural compensatory responses via a ratchet-like effect. This ratchet-like effect then pushes species population dynamics far away from equilibria that can lead to precipitous local extinction.

ecology↗

bioRxiv2020

Ecosystem Entanglement and the Propagation of Nutrient-Driven Instability

Almost 50 years ago, Michael Rosenzweig pointed out that nutrient addition can destabilize food webs, leading to loss of species and reduced ecosystem function through the paradox of enrichment. Around the same time, David Tilman demonstrated that increased nutrient loading would also be expected to cause competitive exclusion leading to deleterious changes in food web diversity. While both concepts have greatly illuminated general diversity-stability theory, we currently lack a coherent framework to predict how nutrients influence food web stability across a landscape. This is a vitally important gap in our understanding, given mounting evidence of serious ecological disruption arising from anthropogenic displacement of resources and organisms. Here, we combine contemporary theory on food webs and meta-ecosystems to show that nutrient additions are indeed expected to drive loss in stability and function in human-impacted regions. However, this loss in stability occurs not just from wild oscillations in population abundance, but more frequently from the complete loss of an equilibrium due to edible plant species being competitively excluded. In highly modified landscapes, spatial nutrient transport theory suggests that such instabilities can be amplified over vast distances from the sites of nutrient addition. Consistent with this theoretical synthesis, the empirical frequency of these distant propagating ecosystem imbalances appears to be growing. This synthesis of theory and empirical data suggests that human modification of the Earths ecological connectivity is "entangling" once distantly separated ecosystems, causing rapid, expansive, and costly nutrient-driven instabilities over vast areas of the planet. The corollary to this spatial nutrient theory, though -- akin to weak interaction theory from food web networks -- is that slow spatial nutrient pathways can be potent stabilizers by moderating flows across a landscape.

ecology↗