Does reaction-diffusion support the duality of fragmentation effect?

TL;DR

This paper investigates how habitat fragmentation affects population dynamics within reaction-diffusion models, revealing that fragmentation can have both positive and negative effects depending on the removal or harvesting strategy.

Contribution

It demonstrates that reaction-diffusion models can support the duality of fragmentation effects, contrasting with traditional predictions of solely negative impacts.

Findings

Fragmented reserves increase population sizes with constant removal.

Aggregated reserves yield higher populations with proportional removal.

Maximum yields occur on fragmented reserves at intermediate harvesting levels.

Abstract

There is a gap between single-species model predictions, and empirical studies, regarding the effect of habitat fragmentation per se, i.e., a process involving the breaking apart of habitat without loss of habitat. Empirical works indicate that fragmentation can have positive as well as negative effects, whereas, traditionally, single-species models predict a negative effect of fragmentation. Within the class of reaction-diffusion models, studies almost unanimously predict such a detrimental effect. In this paper, considering a single-species reaction-diffusion model with a removal -- or similarly harvesting -- term, in two dimensions, we find both positive and negative effects of fragmentation of the reserves, i.e. the protected regions where no removal occurs. Fragmented reserves lead to higher population sizes for time-constant removal terms. On the other hand, when the removal term is proportional to the population density, higher population sizes are obtained on aggregated reserves, but maximum yields are attained on fragmented configurations, and for intermediate harvesting intensities.