Anthropogenic effect recorded in the live-dead compositional fidelity of land snail assemblages from San Salvador Island, Bahamas

Abstract

Terrestrial malacofaunas that inhabit islands are vulnerable to human activities. Habitat destruction, introduction of exotic species, predators, etc. are distorting the composition and distribution of indigenous snail communities. Specifically, the taxonomic discordance between live and dead assemblages may be the consequence of anthropogenic disturbances rather than natural post-mortem processes. Live-dead fidelity may hence reflect the degree of human alteration in a given locality. This approach was used to study the relative abundance of live and dead land snails from pristine and urbanized localities around San Salvador Island (Bahamas). Thirteen species were encountered from 64 samples containing 5,343 specimens. Taxonomic composition was significantly different between areas of negligible anthropogenic disturbance and those impacted by humans. Although which species of land snails are endemic to San Salvador is unknown, all identified species are native to the Caribbean region and invasive species were not encountered. However, some synanthropic species, found exclusively in urban-developed areas, have not been recovered from the local fossil record, pointing to their relatively recent introduction possibly from nearby islands. Non-metric MDS, Jaccard-Chao index, and Spearman correlation analyses indicated that dead assemblages displayed a good compositional correspondence to live communities at pristine sites, whereas considerable disparity was sometimes observed at human-modified areas. Urbanized areas probably favored the proliferation of synanthropic species whereas dead assemblages may contain anthropophobic taxa that lived there prior to recent human modification. These findings are consistent with previous live-dead fidelity studies of marine molluscan and terrestrial small-mammal assemblages, and suggest that the taxonomic discordance between live and dead assemblages of land snails may be indicative of recent anthropogenic alteration.

Conservation Paleobiology: Leveraging Knowledge of the Past to Inform Conservation and Restoration

“…Discordances in the presence and relative abundances of species between living communities and time-averaged death assemblages collected from surficial sediments are also well-established signs of recent changes in the living community. Rather than signifying postmortem bias in preservation, large "live-dead" differences reflect recent, decadal-to centennial-scale changes in the composition and richness of living communities, often driven by eutrophication, climate and habitat change, introduction of invasives, and exploitation (Kidwell 2007(Kidwell , 2013Western & Behrensmeyer 2009;Terry 2010;Miller 2011;Yanes 2012; for review, see Kidwell & Tomasovych 2013). …”

“…For example, when species that possess preservable skeletal hardparts are present alive but absent in a local death assemblage, a new community state or biotic invasion is suspected (e.g., Yanes 2012). Similarly, when abundant dead individuals of a species are found but no living individuals are encountered, local extirpation is suspected.…”

What can we infer from the shell dimensions of the thick-shelled river mussel Unio crassus?

“…The shells and their characteristics are very useful in paleobiology and evolutionary biology because they form a rich fossil record (Sparks, 1961) furnishing invaluable information on the phylogenesis of this group, its past biodiversity (e.g., Kidwell, 2001Kidwell, , 2002, and extinction risk (Harnik, 2011). Because mollusks' relation to their paleohabitat can be extrapolated from the ecology of contemporary species, the ecological conditions of past geological epochs can be inferred from fossil shells (Leonard-Pingel et al, 2012, Yanes, 2012. The shells themselves have been used as environmental archives, and they also contain metabolic signals (Mutvei &Westermark, 2001;Geist et al, 2005a).…”

Assinaturas tafonômicas em moluscos recentes e seu significado paleoambiental

“…Moluscos estuarinos e continentais possuem preservação variável, muitas vezes deixando menos espé-cies em acumulações fossilizáveis (Cummins 1994, Martello et al 2006, Yanes 2012, Tietze e De Francesco 2012, Ritter e Erthal 2013, 2016. Porém, em ambientes marinhos rasos subtropicais, como a parte sul da Amé-rica do Sul, ainda são raros os estudos tafonômicos, com exceção de alguns trabalhos de pesquisadores na Argentina (Aguirre et al 2011, Archuby et al 2015.…”