Testing hypotheses on the ecological patterns of rarity using a novel model of study: snake communities worldwide

Abstract

The theoretical and empirical causes and consequences of rarity are of central importance for both ecological theory and conservation. It is not surprising that studies of the biology of rarity have grown tremendously during the past two decades, with particular emphasis on patterns observed in insects, birds, mammals, and plants. I analyse the patterns of the biology of rarity by using a novel model system: snake communities worldwide. I also test some of the main hypotheses that have been proposed to explain and predict rarity in species. I use two operational definitions for rarity in snakes: Rare species (RAR) are those that accounted for 1% to 2% of the total number of individuals captured within a given community; Very rare species (VER) account for ≤1% of individuals captured. I analyse each community by sample size, species richness, continent, climatic region, habitat and ecological characteristics of the RAR and VER species. Positive correlations between total species number and the fraction of RAR and VER species and between sample size and rare species in general were found. As shownin previous insect studies, there is a clear trend for the percentage of RAR and VER snake species to increase in species-rich, tropical African and South American communities. This study also shows that rare species are particularly common in the tropics, although habitat type did not influence the frequency of RAR and VER species. This analysis also confirms the commonly accepted ecological hypothesis that body size and rarity are clearly and widely correlated in natural animal communities. However, in snake communities there is often an association between large and small species among the rare species, and a tendency for ophiophagous species to be rare. In addition, there was no support for the hypothesis that rare species should be typically phylogenetically primitive. The hypothesis that species with narrower realized ecological niches are more likely to be rare or very rare is supported by the evidence presented here on snake communities. In general, this study shows that snakes may make ”model organisms” for studies on the biology of rarity

Ecological correlates of species richness and population abundance patterns in the amphibian communities from the Albertine Rift, East Africa

“…Ecological characteristics of the study species (i.e., habitat, micro-habitat, and type of activity) were also considered for each of the study species because these species-specific characteristics are known to influence abundance and species richness patterns in other ectothermic vertebrates (e.g., snakes, see Akani et al 1999;Luiselli 2006). So, similarly to what has been done previously with birds (Bennun et al 2002), each amphibian species was assigned to an ecological/habitat type.…”

“…In particular, very few such studies have been performed as for the Eastern African tropics (but see Howell 1993;Poynton et al 2007), despite the crucial relevance of this type of research in terms of both ecological knowledge and conservation (Newmark 2002). On the other hand, studies dealing with community structure and assembly rules have been performed on Afrotropical amphibians (e.g., Ernst and Rödel 2005, 2006, Gardner 2007Behangana and Luiselli 2008).…”

Composition and structure of a snake assemblage in an altered tropical forest-plantation mosaic in Bangladesh

“…Available studies documented such disparate aspects as species composition within particular sites (Orlov, 1995(Orlov, , 1997, diversity and rarity patterns (Akani et al, 1999;Luiselli, 2006a), and the role of resource partitioning and interspecific competition as a key factor in the ecology of these assemblages (Kadowaki, 1996;Luiselli et al, 1998;Laurent and Kingsbury, 2003;Luiselli, 2006b). In recent years, studies of tropical snake assemblages have grown tremendously, particularly in Africa and South America (for quantitative reviews, see Luiselli, 2006aLuiselli, , 2006bLuiselli, , 2008. On the other hand, Asian tropical snake assemblages have remained less profoundly investigated, although some studies, mainly with taxonomic emphasis, are available (Orlov, 1995(Orlov, , 1997Rooijen, 2009;Kams et al, 2010;Kamnarathna and Amarasinghe, 2011).…”

“…Quantitative field studies of snake assemblages have greatly expanded in number and scope during the past 20 years (Luiselli, 2006a(Luiselli, , 2006b and references therein), after a long period of time in which these animals were neglected in terms of community ecology studies (but see Barbault, 1971;Hebrard, 1977a, 1977b). Available studies documented such disparate aspects as species composition within particular sites (Orlov, 1995(Orlov, , 1997, diversity and rarity patterns (Akani et al, 1999;Luiselli, 2006a), and the role of resource partitioning and interspecific competition as a key factor in the ecology of these assemblages (Kadowaki, 1996;Luiselli et al, 1998;Laurent and Kingsbury, 2003;Luiselli, 2006b).…”

“…Our aims with this study are to test the occurrence of some major patterns which were highlighted by earlier studies on tropical snake community ecology (Luiselli, 2006a(Luiselli, , 2006b(Luiselli, , 2008, by using a snake assemblage from a tea plantation/altered forest habitat in Bangladesh. More specifically, we examine a series of relevant hypotheses.…”