Species coexistence in resource‐limited patterned ecosystems is facilitated by the interplay of spatial self‐organisation and intraspecific competition

The exploration of mechanisms that enable species coexistence under competition for a sole limiting resource is widespread across ecology. Two examples of such facilitative processes are intraspecific competition and spatial self-organisation. These processes determine the outcome of competitive dynamics in many resource-limited patterned ecosystems, classical examples of which include dryland vegetation patterns, intertidal mussel beds and Subalpine ribbon forests. Previous theoretical investigations have explained coexistence within patterned ecosystems by making strong assumptions on the differences between species (e.g. contrasting dispersal behaviours or different functional responses to resource availability). In this paper, I show that the interplay between the detrimental effects of intraspecific competition and the facilitative nature of self-organisation forms a coexistence mechanism that does not rely on species-specific assumptions and captures coexistence across a wide range of the environmental stress gradient. I use a theoretical model that captures the interactions of two generic consumer species with an explicitly modelled resource to show that coexistence relies on a balance between species' colonisation abilities and their local competitiveness, provided intraspecific competition is sufficiently strong. Crucially, the requirements on species' self-limitation for coexistence to occur differ on opposite ends of the resource input spectrum. For low resource levels, coexistence is facilitated by strong intraspecific dynamics of the species superior in its colonisation abilities, but for larger volumes of resource input, strong intraspecific competition of the locally superior species enables coexistence. Results presented in this paper also highlight the importance of hysteresis in understanding tipping points, in particular extinction events. Finally, the theoretical framework provides insights into spatial species distributions within single patches, supporting verbal hypotheses on coexistence of herbaceous and woody species in dryland vegetation patterns and suggesting potential empirical tests in the context of other patterned ecosystems.

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Intraspecific competition in models for vegetation patterns: Decrease in resilience to aridity and facilitation of species coexistence

Ecological Complexity ◽

10.1016/j.ecocom.2020.100835 ◽

2020 ◽

Vol 42 ◽

pp. 100835

Author(s):

L. Eigentler

Keyword(s):

Intraspecific Competition ◽

Species Coexistence ◽

Vegetation Patterns

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Higher order interactions and coexistence theory

10.1101/748517 ◽

2019 ◽

Author(s):

Pragya Singh ◽

Gaurav Baruah

Keyword(s):

Intraspecific Competition ◽

Species Coexistence ◽

General Rule ◽

Higher Order ◽

Volterra Model ◽

Ecological Communities ◽

Coexistence Theory ◽

Wide Range ◽

Analytical Result ◽

Underlying Mechanisms

AbstractHigher order interactions (HOIs) have been suggested to stabilize diverse ecological communities. However, their role in maintaining species coexistence from the perspective of modern coexistence theory is unknown. Here, using a three-species Lotka-Volterra model, we derive a general rule for species coexistence modulated by HOIs. We show that negative HOIs that intensify pairwise competition, can promote coexistence across a wide range of fitness differences, provided that HOIs strengthen intraspecific competition more than interspecific competition. In contrast, positive HOIs that alleviate pairwise competition can also stabilize coexistence across a wide range of fitness differences, irrespective of differences in strength of inter- and intraspecific competition. Furthermore, we extend our three-species analytical result to multispecies competitive community and show, using simulations, that feasible multispecies coexistence is possible provided that strength of negative intraspecific HOIs is higher than interspecific HOIs. In addition, multispecies communities, however, become unstable with positive HOIs as such higher-order interactions could lead to disproportionately infeasible growth rates. This work provides crucial insights on the underlying mechanisms that could maintain species diversity and links HOIs with modern coexistence theory.

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Competitive ecosystems are robustly stabilized by structured environments

10.1101/2020.03.09.983395 ◽

2020 ◽

Author(s):

Tristan Ursell

Keyword(s):

Computational Models ◽

Species Coexistence ◽

Physical Structure ◽

Microbial Consortia ◽

Natural Environments ◽

Competing Species ◽

Interspecies Competition ◽

Engineering Structures ◽

Resource Limited ◽

Physical Environments

ABSTRACTNatural environments, like soils or the mammalian gut, frequently contain microbial consortia competing within a niche, wherein many species contain genetic mechanisms of interspecies competition. Recent computational work suggests that physical structures in the environment can stabilize competition between species that would otherwise be subject to competitive exclusion under isotropic conditions. Here we employ Lotka-Volterra models to show that physical structure stabilizes large competitive ecological networks, even with significant differences in the strength of competitive interactions between species. We show that for stable communities the length-scale of physical structure inversely correlates with the width of the distribution of competitive fitness, such that physical environments with finer structure can sustain a broader spectrum of interspecific competition. These results highlight the generic stabilizing effects of physical structure on microbial communities and lay groundwork for engineering structures that stabilize and/or select for diverse communities of ecological, medical, or industrial utility.AUTHOR SUMMARYNatural environments often have many species competing for the same resources and frequently one species will out-compete others. This poses the fundamental question of how a diverse array of species can coexist in a resource limited environment. Among other mechanisms, previous studies examined how interactions between species – like cooperation or predation – could lead to stable biodiversity. In this work we looked at this question from a different angle: we used computational models to examine the role that the environment itself might play in stabilizing competing species. We modeled how species arrange themselves in space when the environment contains objects that alter the interfaces along which competing species meet. We found that these ‘structured’ environments stabilize species coexistence, across a range of density of those objects and in a way that was robust to differing strengths of interspecies competition. Thus, in addition to biological factors, our work presents a generic mechanism by which the environment itself can influence ecological outcomes and biodiversity.

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Higher order interactions and species coexistence

Theoretical Ecology ◽

10.1007/s12080-020-00481-8 ◽

2020 ◽

Author(s):

Pragya Singh ◽

Gaurav Baruah

Keyword(s):

Intraspecific Competition ◽

Species Interactions ◽

Species Coexistence ◽

General Rule ◽

Higher Order ◽

Volterra Model ◽

Ecological Communities ◽

Wide Range ◽

Analytical Result ◽

Underlying Mechanisms

AbstractHigher order interactions (HOIs) have been suggested to stabilize diverse ecological communities. However, their role in maintaining species coexistence from the perspective of modern coexistence theory is not known. Here, using generalized Lotka-Volterra model, we derive a general rule for species coexistence modulated by HOIs. We show that where pairwise species interactions fail to promote species coexistence in regions of extreme fitness differences, negative HOIs that intensify pairwise competition, however, can promote coexistence provided that HOIs strengthen intraspecific competition more than interspecific competition. In contrast, positive HOIs that alleviate pairwise competition can stabilize coexistence across a wide range of fitness differences, irrespective of differences in strength of inter- and intraspecific competition. In addition, we extend our three-species analytical result to multispecies communities and show, using simulations, that multispecies coexistence is possible provided that strength of negative intraspecific HOIs is higher than interspecific HOIs. Our work sheds light on the underlying mechanisms through which HOIs can maintain species diversity.

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