Relationship between beach morphodynamics and body traits in a sand-dwelling wolf spider

Abstract

Sandy beach macrofaunal communities are mainly structured by the independent response of species to the harsh physical environment. The theoretical framework for sandy beach ecology has been mainly developed on the basis of the outstanding role of morphodynamic factors on resident fauna in this narrow land-sea interface. In the case of supralittoral species, the habitat safety hypothesis (HSH) predicts an increase in body size and weight (among several individual and population attributes) from dissipative beaches (fine sand, gentle slope) to reflective beaches (coarse sand, steep slope). Spiders are relevant components of coastal ecosystems due to their strict dependence on prey availability and their carnivore condition; however, the HSH has never before been tested in this taxonomic group. We studied the relationship between beach morphodynamics and body size, weight and body condition of the wolf spider Allocosa marindia. We performed simultaneous collections of adults of A. marindia in two contiguous estuarine beaches with contrasting morphodynamics. As males were scarce, we measured and weighed only females. In agreement with predictions of the HSH, individuals were larger and heavier at the reflective beach. Individual size, weight and body condition were higher at the beginning of the reproductive period. Reflective beaches would act as more benign environments, providing secure microhabitats for the individuals and their potential prey, while affecting positively body traits during development. Our results provide the first formal testing of the HSH in a sand-dwelling spider on beaches with contrasting morphodynamics.