Biology subjects

de Roos, A. M.

Publications and source records attributed to de Roos, A. M..

4 recordsLinked to original sources

bioRxiv2021

Resonance in physiologically structured population models

Ecologists have long sought to understand how the dynamics of natural populations are affected by the environmental variation those populations experience. A transfer function is a useful tool for this purpose, as it uses linearization theory to show how the frequency spectrum of the fluctuations in a populations abundance relates to the frequency spectrum of environmental variation. Here, we show how to derive and to compute the transfer function for a continuous-time model of a population that is structured by a continuous individual-level state variable such as size. To illustrate, we derive, compute, and analyze the transfer function for a size-structured population model of stony corals with open recruitment, parameterized for a common Indo-Pacific coral species complex. This analysis identifies a sharp multi-decade resonance driven by space competition between existing coral colonies and incoming recruits. The resonant frequency is most strongly determined by the rate at which colonies grow, and the potential for resonant oscillations is greatest when colony growth is only weakly density-dependent. While these resonant oscillations are unlikely to be a predominant dynamical feature of degraded reefs, they suggest dynamical possibilities for marine invertebrates in more pristine waters. The size-structured model that we analyze is a leading example of a broader class of physiologically structured population models, and the methods we present should apply to a wide variety of models in this class.

ecology↗

bioRxiv2020

A general approach for analysis of physiologically structured population models: the R package 'PSPManalysis'

SummaryHow environmental conditions affect the life history of individual organisms and how these effects translate into dynamics of population and communities on ecological and evolutionary time scales is a central question in many eco-evolutionary studies.Physiologically structured population models (PSPMs) offer a theoretical approach to address such questions as they are built upon a function-based model of the life history, which explicitly describes how life history depends on individual traits as well as on environmental factors. PSPMs furthermore explicitly account for population feedback on these environmental factors, which translates into density-dependent effects on the life history. PSPMs can thus capture life histories in quite some detail but lead to population-level formulations in terms of partial differential equations that are generally hard to analyse.Here I present a general methodology and a R software package for computing how the ecological steady states of PSPMs depend on model parameters and to detect bifurcation points in the computed curves where dynamics change drastically. The package makes specifying the population model unnecessary and only requires a relatively straightforward implementation of the life history functions as input. It furthermore allows for analysing the evolutionary dynamics and evolutionary singular states of the PSPMs based on Adaptive Dynamics theory.Given the central role of the individual life history in many studies, there is substantial scope for using the presented methodology in fields as diverse as ecology, ecotoxicology, conservation biology and evolutionary biology, where it has already been applied to problems like the evolution of cannibalism, niche shifts and metamorphosis.Competing Interest StatementThe authors have declared no competing interest.View Full Text

ecology↗

bioRxiv2020

Dynamic population stage-structure stabilizes complex ecological communities

SummaryNatural ecological communities are diverse, complex and often surprisingly stable, but the mechanisms underlying their stability remain a theoretical enigma1-5. Interactions such as competition and predation presumably structure communities6, yet theory predicts that complex communities are only stable when species growth rates are mostly limited by intraspecific self-regulation rather than by interactions with resources, competitors and predators3,5,7. Current theory, however, only considers the network topology of population-level interactions between species and neglects within-population differences among juvenile and adult individuals. Here, using model simulations, I show that including commonly observed differences in vulnerability to predation and foraging efficiency between juvenile and adult individuals results in up to ten times larger, more complex communities than in simulations without population stage-structure. These diverse communities are stable or fluctuate with limited amplitude, even though in the model only a single basal species is self-regulated and the population-level interaction network is highly connected. Analysis of the species interaction matrix predicts the simulated communities to be unstable but extending the matrix with a population structure subsystem reveals that dynamic changes in population stage-structure completely cancel out this instability. Common differences between juveniles and adults and fluctuations in their relative abundance hence have a decisive influence on the stability of complex natural communities and their vulnerability when environmental conditions change. Thus, community persistence can not be explained by the network of interactions between the constituting species alone.Competing Interest StatementThe authors have declared no competing interest.View Full Text

ecology↗

bioRxiv2020

Stony coral populations are more sensitive tochanges in vital rates in disturbed environments

Reef-building corals, like many long-lived organisms, experience environmental change as a combination of separate but concurrent processes, some of which are gradual yet long-lasting, while others are more acute but short-lived. For corals, some chronic environmental stressors, such as rising temperature and ocean acidification, are thought to induce gradual changes in colonies vital rates. Meanwhile, other environmental changes, such as the intensification of tropical cyclones, change the disturbance regime that corals experience. Here, we use a physiologically structured population model to explore how chronic environmental stressors that impact the vital rates of individual coral colonies interact with the intensity and magnitude of disturbance to affect coral population dynamics and cover. We find that when disturbances are relatively benign, intraspecific density dependence driven by space competition partially buffers coral populations against gradual changes in vital rates. However, the impact of chronic stressors is amplified in more highly disturbed environments, because disturbance weakens the buffering effect of space competition. We also show that coral cover is more sensitive to changes in colony growth and mortality than to external recruitment, at least in non-self-seeding populations, and that space competition and size structure mediate the extent and pace of coral-population recovery following a large-scale mortality event. Understanding the complex interplay among chronic environmental stressors, mass-mortality events, and population size structure sharpens our ability to project coral dynamics in an increasingly disturbed future.

ecology↗