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, Almería, Spain. Fragments were classified into three size classes (< 300, 300-900, and > 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.

Patterns of seed dispersal syndromes on serpentine soils: examining the roles of habitat patchiness, soil infertility and correlated functional traits

“…Using multiple data sets gave us the ability to distinguish effects of different aspects of the environment on dispersal syndromes including habitat quality, habitat patchiness and vegetation type. Several studies of humanfragmented landscapes have shown that species with more directed (vertebrate) dispersal are less vulnerable to fragmentation (Damschen et al 2008;Montoya et al 2008;Alados et al 2010). Our results suggest that communities on discontinuous patches of low-fertility soils are not necessarily composed of good dispersers.…”

Ecological and socio-economical thresholds of land and plant-community degradation in semi-arid Mediterranean areas of southeastern Spain

“…This is especially relevant in arid areas where species that have a restricted spatial dispersal are abundant because the space suitable for germination is scarce and it is advantageous to germinate close to the mother plant (Van Rheede van Outshoorn and Van Rooyen, 1999). Consequently, species that have restricted spatial dispersal (reduction of dispersal mechanisms or have anchorage mechanisms), which are predominant in arid regions (Ellner and Shmida, 1981;Gutterman, 1993;Navarro et al, 2009), are very sensitive to habitat fragmentation (Alados et al, 2010). In semi-arid areas in southeastern Spain, the isolation of remnant fragments had a negative effect on plant species richness (Alados et al, 2009a) and led to an increase in the differences in species composition among fragments (spatial variability in species distributions was greater than that expected from a random spatial distribution).…”

The conservation physiology of seed dispersal

“…These conclusions on seed dispersal by trees might not apply universally. In contrast to Montoya et al [37], Alados et al [38] found that vertebrate-dispersed shrubs were more susceptible to fragmentation than other shrubs. The authors postulated that the reason for this was positive feedback between the abundance of a fruiting species on a given patch and the ability of that patch to attract appropriate animal seed dispersers (i.e.…”