Habitat fragmentation often forces animals to cross the potentially dangerous environment in between patches of habitat – the area known as the matrix.
Due to differences in composition and configuration, the matrix can vary in the degree to which it restricts movement. For example, an urban matrix of roads and buildings that surrounds a patch of forest is likely to be more of a barrier to a deer’s movement than an agricultural matrix of crops.
Rohwäder, M.S., Gallagher, C. and Jeltsch, F. 2024. Variations in risk‐taking behaviour mediate matrix mortality’s impact on biodiversity under fragmentation. Ecography, p.e07140.
Two main variables determine how a matrix will affect species movement. First, what is the risk of mortality for an individual crossing the matrix (e.g. risk of predation, risk of vehicle collisions)? Second, how does an individual animal behave in response to the matrix? Some individuals will be bolder and more willing to enter the matrix, while others will be risk-averse. Together, the risk of mortality in the matrix and an individual’s behavioral response to the matrix influence how the matrix in a fragmented landscape affects biodiversity.
In a new study, researchers used a modeling approach to examine how habitat fragmentation, the quality of the matrix, and risk-taking behavior of individual animals interact to shape the diversity of ecological communities. To disentangle the effects of fragmentation, the mortality risk of the matrix, and individual behavioral responses to the matrix, researchers modeled communities of small herbivorous mammals. The model simulates the behavior of hypothetical individuals belonging to several small mammal species that are competing for a common food resource.
These communities were simulated under different scenarios of landscape fragmentation (weakly to highly fragmented), matrix mortality (low to high risk of mortality) and behavioral traits (different distributions of individual risk-taking probability). Researchers then measured the biodiversity of the communities after a period of 20 years.
Results of the simulations show that the risk of the mortality in the matrix determined whether fragmentation reduced or bolstered biodiversity. When mortality risk was low, fragmentation had a positive effect on biodiversity, but when mortality risk was high, fragmentation negatively impacted biodiversity. When landscapes were weakly fragmented, biodiversity of the communities was highly stable, even when the matrix was risky.
The behavior of individuals in the community also regulated biodiversity: communities that were behaviorally diverse were more immune to the harmful impacts of fragmentation and matrix mortality. In highly fragmented landscapes, the individuals in the simulated communities became more risk-taking because they needed to cross the matrix to meet their resource needs.
However, as the matrix became more risky in these simulated landscapes, communities became more behaviorally heterogenous to avoid matrix mortality. This implies that over the long-term, fragmentation could influence the evolution of risk-taking traits in ecological communities.
Together, these results highlight how fragmentation and the matrix interact to impact biodiversity. A more or less risky matrix could intensify the effects of fragmentation. Managing the land in between habitat patches so that it’s less risky to organisms can ameliorate some of the risks of habitat fragmentation.
However, it may not always be possible to make the matrix less risky. Corridors can reduce the impacts of fragmentation and a dangerous matrix by facilitating the movement of organisms through the matrix.
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