Abstract
Organisms with different life-histories and abilities to disperse often utilise habitat patches in different ways. We investigated the influence of the size of patches of rock (separated by stretches of sand) on the density of pulmonate limpets (Siphonaria spp.) along 1500 km of the linear landscape of the South African coastline. We compared the influence of patch-size on two congeneric species with different modes of development, S. serrata a direct developer, and S. concinna a planktonic developer. We tested the spatial and temporal consistency of the effects of patch-size by sampling 7 independent regions spanning the distributional range of both species of limpets, and by sampling one region at monthly intervals for 1 year. Within each region or month, 4 small patches (<20 m in length) interspersed with the 4 large patches (>60 m in length) were sampled. Across the entire geographic range and throughout the year, there were more of both species of limpets in large patches than in small patches. In most regions, there was greater variability in large patches than small patches. Variability within patches in a single region was similar throughout the year, with greater variability of both species in large than in small patches. We found little influence of the mode of development on the response of limpets to patch-size. Our findings highlight the importance of understanding patterns of distribution of species with respect to habitat heterogeneity in linear landscapes, and contradict the idea that organism mobility at an early ontogenetic stage directly affects habitat use.
Highlights
Habitat loss and fragmentation are generally considered to be among the major threats to biodiversity [1]
There was a significant effect of Region by Size (Table 1) with a greater density of adult limpets in large patches than small patches in most regions (Fig. 2) but this was only significant in the Eastern Cape (Table 1)
The most striking pattern from this study, encompassing regional scales of 1500 km and temporal sampling for one year, is that two species with distinctly different modes of development and very different potential for dispersal generally showed the same responses to patch size. This suggests that siphonarian limpets respond to factors influencing their survival rather than processes influencing their arrival at patches
Summary
Habitat loss and fragmentation are generally considered to be among the major threats to biodiversity [1]. Dispersal can include adult motility, and the effects of life-history on the ability to disperse at different ontogenetic stages. Previous studies suggest that organisms with different dispersal abilities and life-history strategies utilise different types of habitat patches [3,4]. Meyer & Posey [4] found that two species of fish with contrasting dispersal abilities and life-histories utilised patches of marshes and shallow water flats habitats differently. Information on how organisms perceive and respond to changes in a landscape, and the ways in which behavioural and life-history traits influence responses to habitat heterogeneity is needed in order to predict the effects of habitat change on populations [5,6]
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