Dispersal movement through fragmented landscapes: the role of stepping stones and perceptual range

Abstract

Context: Dispersal is a crucial process for species persistence under natural and disturbed landscapes. The effectiveness of stepping stones as a connectivity strategy for increasing dispersal success depends on landscape structure and animal behaviour, such as the perceptual range. Objectives: We quantify the relative contribution of stepping stones (small fragments and scattered trees) to dispersal success considering interactions with perceptual range, habitat amount and configuration. Methods: We develop an individual-based model (IBM) to simulate the dispersal movement of small mammals. The model is parametrized using empirical estimates of perceptual range and movement properties (turning angles and steps length). Simulations are implemented in landscapes with varying gradients of habitat amount and clumpiness, with and without the presence of stepping stones. Results: Small patches and scattered trees combined, or only scattered trees, have a positive effect on dispersal. Meanwhile, the presence of only small patches has negative effects on dispersal. Habitat amount positively influences dispersal, which decreases abruptly when the habitat amount is less than 20%. This threshold disappears in the presence of stepping stones. In landscapes with intermediate levels of habitat amount, landscape fragmentation (low clumpiness) has a positive effect on dispersal success. Conclusions: Stepping stones, especially scattered trees, are a fundamental connectivity strategy for the conservation of small non-flying vertebrates in human-modified landscapes, particularly landscapes with less than 20% of habitat amount. However, small patches stepping stones may act as ecological traps leading the individuals to dead-ends. Their effectiveness in improving dispersal depends on both landscape structure and perceptual range.