Dispersal abilities and spatial patterns in fragmented landscapes

Abstract

Recent theoretical studies suggest that the distribution of species in space has important implications for the conservation of communities in fragmented landscapes. Facilitation and dispersal are the primary mechanisms responsible for the formation of spatial patterns. Furthermore, disruptions in the formation of patterns arise after degradation, which can serve as an early indicator of stress in plant communities. Spatial dispersal ability and pattern formation were evaluated in 53 linear transects of 500 m in length within 14 fragments of natural vegetation within a matrix of abandoned crop fields in Cabo de Gata National Park, Almeria, Spain. Fragments were classified into three size classes ( 900 ha). Fragment connectivity was quantified using the distances between fragments. Spatial dispersal ability was quantified for the 187 species recorded in the study. Species with restricted dispersal had the highest degree of long-range spatial autocorrelation and, species that disperse by biotic vectors (e.g. vertebrates), the lowest. In addition, species most susceptible to fragmentation are vertebrate-dispersed shrubs, which declined in abundance and was associated with loss of spatial organization in the smallest fragments. It is postulated that the positive feedback between abundance of recruitment and vertebrate visits influences the colonization and persistence of vertebrate-dispersed shrubs, explaining its abundance in large fragments. Indeed, fragments lower than a certain threshold reduced spatial organization not only in shrubs with biotic dispersal, but also in species with abiotic dispersal (mainly wind) and with restricted dispersal. Fragments lower than a certain threshold may be vulnerable to a cascade of species loss because of reduced recruitment, establishment and patch biomass as a result of natural senescence, finally breaking up facilitative plant interactions.