ECOP Subgroup Contributed Talks

Brendon McGuinness

McGill University

"Optimization of resource consumption traits shape community structure and the strength of niche and neutral processes in competitive communities"

Resource competition theory has overlooked the feedbacks that emerge from organisms shaping their environment through resource consumption, which in turn, shape plastic changes in traits in direct response to environmental variation. Community ecology has yet to integrate this feedback to predictions of community structure that include functional diversity and relative abundance distributions. Here we study how plasticity in resource consumption traits, defined by individual energy allocation constraints, shape community structure. We adopt a model incorporating plasticity in classic consumer-resource models where consumption strategies become dynamic state variables through optimizing organism growth by gradient ascent, underpinned by investment constraints in physiological machinery for acquisition of resources. Our results predict how plasticity in resource consumption strategies results in trait dynamics that let species avoid competitors while maximizing its efficiency on available resources. Interestingly this plastic optimization in even just one species in a community allows all other non-plastic species to coexist, a case of positive facilitation with pure competitive interactions. Additionally, we build a simple model based on plasticity maximizing resource uptake while minimizing competition that is predictive of relative species abundances so long as a geometric characteristic that we define as community supply vector distance is above a certain threshold. We study two cases, one where species consumption strategies are predictive of species abundances (niche), and a second in which consumption strategies are not predictive of species abundances (neutral). In the first case, we find that initial consumption strategies are more predictive of relative abundance distributions than equilibrium consumption strategies, highlighting the importance of the consumption strategy species have when colonizing a new environment in determining community structure when these traits are dynamic. Our study suggests that plasticity constrained by individual energy allocation provides a mechanism of facilitation that promote coexistence as well determines the relative strength of niche and neutral processes as drivers of community structure.
Additional authors: Frederic Guichard; Stephanie Weber

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Farshad Shirani

Georgia Institute of Technology

"Competition, Phenotypic Adaptation, and the Evolution of a Species’ Range"

Geographic ranges of communities of species evolve in response to environmental, ecological, and evolutionary forces. Understanding the effects of these forces on species’ range dynamics is a major goal of spatial ecology. Previous mathematical models have jointly captured the dynamic changes in species’ population distributions and the selective evolution of fitness-related phenotypic traits in the presence of an environmental gradient. These models inevitably include some unrealistic assumptions, and biologically reasonable ranges of values for their parameters are not easy to specify. As a result, simulations of the seminal models of this type can lead to markedly different conclusions about the behavior of such populations, including the possibility of maladaptation setting stable range boundaries. In this talk, we present our works on harmonizing such results by developing and simulating a continuum model of range evolution in a community of species that interact competitively while diffusing over an environmental gradient. Our model extends existing models by incorporating both competition and freely changing intraspecific trait variance. We show that the spatial profile of species’ trait variance that is predicated by our model is consistent with experimental measurements available in the literature. Moreover, we show that our results reaffirm interspecific competition as an effective factor in limiting species’ ranges, even when trait variance is not artificially constrained.
Additional authors: Judith R. Miller (Georgetown University)

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Maud El-Hachem

CSIRO (Commonwealth Scientific and Industrial Research Organisation)

"Coexistence in two-species competition with delayed maturation"

Mortality caused by competition that occurs during maturation is explicitly modelled in some alternative formulations of the Lotka-Volterra competition model. We generalise this approach by using a distributed delay for maturation time. The distributed delay separates the mature from the immature individuals, to represent a species where competition is more important for immature individuals and where maturation time is long compared to lifetime. The resulting system of delay differential equations (DDEs) is transformed into a system of ordinary differential equations (ODEs) using the linear chain approximation. We show how the survival of a species depends on the rate of maturation being able to compensate for the rate of loss due to mortality of adults and immature individuals. A species fit for survival enters into competition with another species, leading to competitive exclusion, to stable coexistence of both species, or to unstable coexistence. We determine the stability conditions using the nullclines method and local stability analysis. The introduction of a distributed delay promotes coexistence and survival of the species compared to the limiting case of a discrete delay, potentially affecting management of relevant pests and threatened species.
Additional authors: Nicholas J. Beeton

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Zhao (Wendy) Wang

McGill University

"Dynamics of a reduced gene regulation model with transport-driven state-dependent delay"

Time-delays arise naturally in biological systems involving transport processes. We study the dynamics of a scalar delay differential equation where the delay induced by transport depends on the state of the system, and is defined implicitly by a threshold condition. The model can be derived from an extended gene regulation model where we found that the inclusion of threshold state-dependent transcription and translation delay enriches the potential operon dynamics in contrast to models with constant delays. We systemically study the various cases when feedback and transport velocity are described by increasing or decreasing (or constant) Hill functions of the state variable. We also examine the stability and bifurcations of the steady states in a limiting case where the Hill function turns into a piecewise constant function. With constant transport velocity, the fold bifurcations always bound the stability of the steady state even in the presence of Hopf bifurcations, while the steady state when unique could lose stability in supercritical Hopf bifurcations. The dynamics with variable transport velocity is more interesting and complex due to the existence of high dimensional bifurcations of the steady states as well as periodic orbits. The steady state could undergo codimension-2 bifurcation such as fold-Hopf bifurcation and Bogdanov–Takens bifurcation that is associated with three codimension-1 bifurcations, Hopf bifurcation, fold bifurcation and homoclinic bifurcation nearby. Understanding the dynamics of the reduced scalar model may help to locate regions where interesting dynamics could occur for the full model.

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