Paths to annihilation: Genetic and demographic consequences of range contraction patterns

Abstract

Species range contractions are important contributors to biological annihilation, yet typically do not receive the same attention as extinctions. Range contractions can lead to marked impacts on populations but are often only characterized by measurements of reduced extent. For effective conservation efforts, it is critical to recognize that not all range contractions are the same. We propose four distinct patterns of range contraction: shrinkage, amputation, hollow, and fragmentation. We tested their impact on populations of a generic generalist species using forward-time simulations. Results showed that all four patterns differentially reduced population abundance (declines of 60-80%) and significantly increased average relatedness, with differing patterns in nucleotide diversity (π) declines relative to the contraction pattern. The fragmentation pattern resulted in the strongest effects on post-contraction genetic diversity and structure. Defining and quantifying range contraction patterns and their consequences for the planet’s biodiversity provides necessary information to combat biological annihilation in the Anthropocene.

Dynamics of reduced genetic diversity in increasingly fragmented populations of Florida scrub jays,Aphelocoma coerulescens

“…Our results highlight how quickly genomic impacts can accumulate during rapid anthropogenic population decline, even in the presence of ongoing gene flow. Habitat loss and fragmentation have been shown to deteriorate genetic diversity at the greatest magnitude relative to other modes of range contraction (Rogan et al, 2021 ). Therefore, we emphasize the importance of conservation intervention in the early stages of population decline, especially given the severity and speed associated with habitat loss and fragmentation.…”