Structure and conservation of Sri Lankan land‐snail assemblages in fragmented lowland rainforest and village home gardens

Abstract

Summary 1.Modified habitats have a profound impact on the biota of fragmented tropical forests. We investigated the structure of land-snail assemblages in Sri Lankan lowland rainforest and village home gardens, a habitat of the surrounding matrix of modified habitats. We focused on four questions, (i) How do the land-snail faunas of lowland rainforest and home gardens differ and can forest species persist in gardens? (ii) Can environmental variables such as altitude, canopy density and soil pH explain significant variation in species composition independent of the effects of habitat type? (iii) What is the extent of geographical species turnover? (iv) How valuable are the two habitats for the conservation of native land snails? 2. Sixty-nine standardized belt transects were sampled in 21 rainforest fragments and 12 gardens. Data were analysed using canonical and partial canonical correspondence analysis. 3. Land-snail species composition varied significantly between gardens and forest. Lowland rainforest was dominated by native snails, many of which were restricted to forest. Gardens contained a distinct component of exotic and native synanthropic snails, as well as many native forest species. Altitude, canopy density and soil pH explained significant variation in species composition independent of the effects of habitat type but were closely correlated with variation in species composition between gardens and forest. Longitude and latitude explained significant variation in species composition across both gardens and forest. 4. Synthesis and applications . Most rainforest snails were restricted to forest. This, together with the high level of geographical turnover and the scale of forest fragmentation, emphasizes the need to conserve all remaining rainforest cover. A substantial number of widespread and localized forest land-snail species can survive in gardens. Home gardens therefore offer great potential for restoring and increasing forest cover and connectivity.

Biodiversity conservation in Sri Lanka's novel ecosystems

“…In a separate investigation, Raheem et al (2008) observed that 17 of 41 endemic land-snail species present in old-growth forest were present in home gardens within the same landscape, a single endemic that occurred in home gardens being absent from the forest.…”

“…An objection potentially levelled against the conservation value of novel ecosystems is that they often harbour alien species (e.g., for land snails see Raheem et al, 2008). Indeed, even in Sri Lanka, grasses, ferns and alien plants feature prominently in successional vegetation (see Gunaratne et al, 2010).…”

Land snails (Mollusca: Gastropoda) of India: status, threats and conservation strategies

“…Even, cutting of roads within a protected area could fragment populations of snails. However, for a subset of forest snail species, man-made habitats such as home gardens and plantations can act as either refugia or corridors between forest patches (Aravind 2005; Raheem et al 2008). Climate change is considered to be a threat to many species (Thomas et al 2004), and land snails are particularly vulnerable (Pounds & Crump 1994;Pounds et al 1999;Sternberg 2000;Bezemer & Knight 2001;Gerlach 2007).…”

Diversity of Hymenoptera, Cultivated Plants and Management Practices in Home Garden Agroecosystems, Kyrgyz Republic

“…Home garden systems are fundamentally different from large scale agriculture: they use no chemical inputs, are not mechanized, and host high levels of diversity including agrobiodiversity, non-cultivated plant diversity, as well as insect, mollusc and bird diversity (e.g., Hylander & Nemomissa 2008, Raheem et al 2008. Improving smallholder farming systems is critical for reducing hunger and poverty through longterm growth in agricultural productivity (Hall 2001).…”

“…Nonetheless, home gardens play two major roles in the conservation of biodiversity at two different scales: within the garden and the garden itself. There can be many different species and varieties of plants within gardens (e.g., Nabhan 1985) while the gardens themselves can serve as habitat for other plant, insect and animal species that are not intentionally planted or tended by households (e.g., Perfecto et al 1996, Hylander and Nemomissa 2008, Raheem et al 2008.…”