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Long-term trends in gastropod abundance and biodiversity: disentangling effects of press versus pulse disturbances

Citation

Willig, Michael; Presley, Steven (2022), Long-term trends in gastropod abundance and biodiversity: disentangling effects of press versus pulse disturbances, Dryad, Dataset, https://doi.org/10.5061/dryad.1zcrjdft4

Abstract

Aim: Climate-induced pulse (e.g., hurricanes) and press (e.g., global warming) disturbances represent threats to populations, communities, and the ecosystem services that they provide. We leveraged three decades of annual data on tropical gastropods to quantify the effects of major hurricanes, associated secondary succession, and global warming on abundance, biodiversity, and species composition.

Location: Luquillo Mountains, Puerto Rico.

Methods: Gastropod abundance, biodiversity, and composition were estimated annually for each of 27 years in a tropical montane forest that experienced three major hurricanes (Hugo, Georges, and Maria). Generalized linear mixed-effects, linear mixed-effects, and linear models evaluated population- and community-level responses to year, ambient temperature, understory temperature, hurricane, and time since hurricane. Variation partitioning determined the unique and shared variation in biotic responses associated with temperature, disturbance, and succession.

Results: Rather than declining, gastropod abundances generally increased through time, whereas the responses of biodiversity were weak and scale dependent. Hurricanes and associated secondary succession, rather than ambient atmospheric temperature, molded long-term trends in abundances and biodiversity.

Main conclusions: Global warming over the past 30 years has not progressed sufficiently to elicit significant responses by gastropods in the Luquillo Mountains. Rather, effects from pulse disturbances (i.e., hurricanes) and secondary succession currently drive long-term variation in abundance and biodiversity. Gastropods evince high resilience in this tropical ecosystem. Historical exposure to recurrent hurricanes likely imbued the fauna with broad niches that make them resistant to current levels of global warming. We predict that biotic resiliency will be challenged once changes in temperature exceed interannual and inter-habitat differences that typify this hurricane-mediated system, or combine with an increased frequency of hurricanes and droughts to alter associations among environmental characteristics that define the fundamental niches of species. Only then might significant declines in abundance or the appearance of novel communities characterize the gastropod fauna in the Luquillo Mountains.

Methods

Gastropods were surveyed annually from 1993 through 2019 at each of 40 points on the LFDP. At each point, all surfaces (rocks, litter, debris, vegetation) within a 3 m radius and up to 3 m of height were inspected for gastropods. Surveys were conducted at night, when terrestrial gastropods are most active (Heatwole & Heatwole, 1978). The same 40 points were surveyed twice in 1993, thrice in 1994, and four times all other years. To minimize alteration of long-term study sites, litter was not manipulated, and specimens were returned as closely as possible to the point of capture. Consequently, our considerations are restricted to gastropods that occur on or above ground litter. Seventeen species of terrestrial gastropod typically occur in these habitats, with some species being undetected in particular years (e.g., Diplosolenodes occidentalis, Obeliscus terebraster, Subulina octona) and other species occurring at over half of the survey points during most years (e.g., Caracolus caracolla, Gaeotis nigrolineata, Nenia tridens). All data are from the Luquillo Long-Term Ecological Research Site, whose collection is supported by the US National Science Foundation (NSF). Gastropod data are archived publicly in accordance with NSF guidelines (https://luq.lter.network/data/luqmetadata107 or https://portal.edirepository.org/nis/mapbrowse?packageid=knb-lter-luq.107.9996737). Additional details on sampling (Willig et al., 1998) and gastropod autecology (Garrison & Willig, 1996) in the Luquillo Experimental Forest are available elsewhere.

Funding

National Science Foundation, Award: BSR-8811902, DEB-9411973, DEB-0080538, DEB-0218039, DEB-0620910, DEB-1239764, DEB-1546686, and DEB-1831952