Step back! Niche dynamics in cave-dwelling predators

Abstract

a b s t r a c tThe geometry of the Hutchinson's hypervolume derives from multiple selective pressures defined, on one hand, by the physiological tolerance of the species, and on the other, by intra-and interspecific competition. The quantification of these evolutionary forces is essential for the understanding of the coexistence of predators in light of competitive exclusion dynamics. We address this topic by investigating the ecological niche of two medium-sized troglophile spiders (Meta menardi and Pimoa graphitica). Over one year, we surveyed several populations in four subterranean sites in the Western Italian Alps, monitoring monthly their spatial and temporal dynamics and the associated physical and ecological variables. We assessed competition between the two species by means of multi regression techniques and by evaluating the intersection between their multidimensional hypervolumes. We detected a remarkable overlap between the microclimatic and trophic niche of M. menardi and P. graphitica, however, the former dbeing larger in sized resulted the best competitor in proximity of the cave entrance, causing the latter to readjust its spatial niche towards the inner part, where prey availability is scarcer ("step back effect"). In parallel to the slight variations in the subterranean microclimatic condition, the niche of the two species was also found to be seasonal dependent, varying over the year. With this work, we aim at providing new insights about the relationships among predators, demonstrating that energypoor environments such as caves maintain the potential for diversification of predators via niche differentiation and serve as useful models for theoretical ecological studies.

Modelling the future spread of native and alien congeneric species in subterranean habitats — the case of Meta cave-dwelling spiders in Great Britain

“…This result is well explained if we take into account the general preference of these spiders for the subterranean habitats in the vicinity of the surface (Novak et al, 2014), where the external meteorological variability still exerts a seasonal influence on the general microclimate. Also, this result is in direct accordance with observations made at a local scale -single cave systems, -pointing out an influence of seasonal climatic variations in the spatial distribution of the spiders within the cave (Mammola et al, 2016a;Lunghi et al, 2017).…”

“…Whilst in recent years there have been a number of studies documenting the ecological requirements of Meta spiders at a local scale (Novak et al, 2010;Mammola & Isaia, 2014;Manenti et al, 2015;Mammola et al, 2016a;Lunghi et al, 2017), the environmental drivers of their broad distributions are still poorly documented. In the only attempt to model the distribution of these species at a continental scale, large scale climatic variables and the competition between the two species were considered as the main factors explaining their broad distribution patterns (Mammola & Isaia, 2017a).…”

“…A strong correlation with limestone areas would indeed only be expected in calciphilous invertebrate species (e.g., certain species of Gastropoda), or those largely restricted to natural caves. In this respect, it is well documented that, aside from caves, Meta spiders are able to thrive in a variety of dark and moist habitats, such as sea caves, mines, cellars, culverts, drainages, railway tunnels, hollow trees, animal burrows, boulder fields and other rocky crevices (Smithers, 1995(Smithers, , 2005a(Smithers, , 2005bRůžika, 1999;Harvey et al, 2002;Růžika & Klimeš, 2005;Mammola & Isaia, 2014;Mammola et al, 2016a;Moseley & Proctor, 2017). This high ecological plasticity may explain why the influence of the geological substrate, in constructing the model, is only limited and, in parallel, why topographic heterogeneity is important in explaining the distribution of these spiders.…”

Mitigating the conflict between pitfall-trap sampling and conservation of terrestrial subterranean communities in caves

“…In caves this especially holds true for trogloxenes and troglophiles, since most of them do not live exclusively in subterranean habitats, a pattern that causes substantial variation in their communities over the year (Di Russo et al, 1999;Novak et al, 2012;Tobin et al, 2013). Seasonal migrations of troglobionts have also been documented between caves and adjacent habitats inaccessible to humans (Juberthie, 1967;Uéno, 1987;Crouau-Roy et al, 1992;Lencioni et al, 2010;Novak et al, 2012;Tobin et al, 2013;Mammola et al, 2015Mammola et al, , 2016. Chao et al (2009) suggest that it is reasonable to set 95% of species as a practical limit in biological surveys.…”

“…The traps are placed on the ground either in groups or in transects. The vertical distribution and dynamics of fauna have only rarely been taken into account in caves (e.g., Novak et al, 2010;Mammola & Isaia, 2016;Mammola et al, 2016). Some species distributions in caves are influenced by microhabitat distribution, even, e.g., by the structural heterogeneity of cave walls (Bourne, 1967;Mammola & Isaia, 2016;Mammola et al, 2016); therefore, various microhabitats should also be considered in such studies.…”