DOI: 10.5061/dryad.1zcrjdft4
title: Long‐term trends in gastropod abundance and biodiversity: Disentangling effects of press versus pulse disturbances

description: 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.
description: 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.,
 <em>Diplosolenodes occidentalis, Obeliscus terebraster, Subulina
 octona</em>) and other species occurring at over half of the survey
 points during most years (e.g., <em>Caracolus caracolla, Gaeotis
 nigrolineata, Nenia tridens</em>). 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.