Demographic effects of aggregation in the presence of a component Allee effect

TL;DR

This paper develops a spatially explicit model to explore how aggregation influences demographic Allee effects, revealing that spatial structure can enhance survival and alter the manifestation of these effects.

Contribution

It introduces a novel theoretical framework where spatial patterns emerge from individual behaviors, linking local interactions to population-level demographic effects.

Findings

Aggregation increases population abundance.

Aggregation enables survival in harsher environments.

Spatial structure can suppress or localize demographic Allee effects.

Abstract

The component Allee effect (AE) is the positive correlation between an organism's fitness component and population density. Depending on the population spatial structure, which determines the interactions between organisms, a component AE might lead to positive density-dependence in the population per capita growth rate and establish a demographic AE. However, existing spatial models impose a fixed population spatial structure, which limits the understanding of how a component AE and spatial dynamics jointly determine the existence of demographic AEs. We introduce a spatially explicit theoretical framework where spatial structure and population dynamics are emergent properties of the individual-level demographic and movement rates. This framework predicts various spatial patterns depending on its specific parameterization, including evenly spaced aggregates of organisms, that determine the demographic-level by-products of the component AE. We find that aggregation increases population abundance and allows population survival in harsher environments and at lower global population densities when compared with uniformly distributed organisms. Moreover, aggregation can prevent the component AE from manifesting at the population level or restrict it to the level of each independent aggregate. These results provide a mechanistic understanding of how component AEs might operate for different spatial structures and manifest at larger scales.