Habitat loss and fragmentation drive global biodiversity loss so being able to forecast species’ responses to the fragmentation of their habitat is a critical conservation goal. The short-term responses of species to fragmentation are frequently used to extrapolate their long-term responses, but theory and accumulating empirical evidence suggest that short-term responses are poor predictors of long-term responses, especially when matrix habitat is dynamic, which is common. We use data for an amphipod, Arcitalitrus sylvaticus, from a long-term, large-scale experiment to ask: can we predict a species’ long-term response from its short-term response by also determining its abiotic niche and predicting how a dynamic matrix, and fragment habitat, will change over time? Amphipods were sampled from the Wog Wog Fragmentation Experiment in southeastern Australia from 1985-1998 and from 2009-2014 using pitfall traps distributed in native continuous Eucalyptus forest, remnant Eucalyptus forest fragments of different sizes within a Pinus radiata managed plantation matrix, and within the pine matrix. We determined the effects of fragmentation on the amphipod and used habitat and microclimate data to model the abiotic niche of the amphipod.
Immediately following fragmentation in 1987, amphipods disappeared from the matrix and declined in abundance in all fragment sizes, except large fragment cores, compared to continuous forest. By 2010, the pine trees in the matrix neared maturity, and the overall impact of fragmentation on amphipod abundance disappeared; abundances in the fragments, matrix, and continuous forest were similar. We determined that A. sylvaticus inhabits habitat with wetter soils and greater canopy cover, which explains why its abundance sharply dropped in fragments and the matrix immediately following clear-cutting and rebounded as the matrix matured and began to approximate the abiotic conditions of the continuous Eucalyptus forest. The dramatic short-term response of the amphipod was a poor predictor of its long-term response. Had we measured the abiotic niche of the amphipod in 1985 and recognized that the maturing pine plantation matrix would eventually shade and cool the Eucalyptus fragments, we could have predicted that the negative impacts of fragmentation on this species should subside over time. Together, abiotic niche models, predicting how the matrix will alter fragments over time, and a species’ short-term response to fragmentation, provide a simple, yet powerful, way to predict the long-term responses of species impacted by habitat fragmentation.