The distribution, spatial clustering, and density of trapdoor spiders in two California coastal dune ecosystems

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  The distribution, spatial clustering, and density of trapdoor spiders in two California coastal dune ecosystems Abstract Coastal dune ecosystems support endemic trapdoor spiders, yet population data for these species are limited. We conducted the first coastal dune trapdoor spider population estimation surveys at Moss Landing State Beach (California) and for Aptostichus stephencolberti Bond 2008 at Sunset State Beach using randomly selected 1m 2 quadrats across ~26,000 m 2 per site. Burrow densities were similar between sites (Sunset: 0.287 burrows/m 2 ; Moss: 0.453 burrows/m 2 ), yielding estimated population sizes of ~35,206 and ~30,959 individuals, respectively. However, spatial analyses revealed contrasting patterns of burrow distribution. At Sunset State Beach, burrow presence was strongly associated with vegetation and occurred closer to plants, despite vegetation being randomly distributed. In contrast, no vegetation–burrow association was detected at Moss Landing, alth...

Double dare: climate change and volcanic activity threatens local populations of Meta menardi (Araneae, Tetragnathidae) in Sicily

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Double dare: climate change and volcanic activity threatens local populations of Meta menardi (Araneae, Tetragnathidae) in Sicily

Abstract

Meta menardi (Latreille, 1804) and M. bourneti Simon, 1922 (Araneae: Tetragnathidae) are ubiquitous inhabitants of the twilight zone of most hypogean sites across Europe. The two species are broadly distributed in Italy, including Sicily, where they show a remarkable segregation along the altitudinal gradient of Mount Etna. Thanks to our recent sampling activities in this area, we create a georeferenced dataset allowing the application of Species Distribution Modelling aiming at evaluating the current and the future habitat in light of the impacts caused by climate change on the local populations. We predicted a relatively wide suitable area for M bourneti, ranging from the sea level up to 1,100 meters a.sl., whereas for M. menardi the suitable area encompasses a narrow mid altitude strip, extending halfway between the areas suitable for M. bourneti, and the highly unsuitable volcanic uplands, heavily disturbed by the volcanic activity. The averaged future predictions for 2070 under RCP 8.5 scenario, show that M. bourneti will expand its range upwards, in areas that are now suitable for M. menardi. In turn, predictions for M. menardi indicate an extreme reduction of the current strip of suitable habitat, likely determining its local extinction. Our findings are further corroborated by the analysis of the bioclimatic niche of the two species assessed via multidimensional Hutchinsonian hypervolume, being much smaller in M. menardi compared to of M. bourneti. In light of our results, it seems likely that having wider climatic preference, M. bourneti will substitute M. menardi in most of its current range in Sicily. Future interventions aiming at the conservation of M. menardi on Mount Etna are strongly advised.


Double dare: climate change and volcanic activity threatens local populations of Meta menardi (Araneae, Tetragnathidae) in Sicily, Global Ecology and Conservation, 2023, e02699, 
ISSN 2351-9894,
https://doi.org/10.1016/j.gecco.2023.e02699.