Effects of habitat history and extinction selectivity on species‐richness patterns of an island land snail fauna

Abstract

Aim Local-scale diversity patterns are not necessarily regulated by contemporary processes, but may be the result of historical events such as habitat changes and selective extinctions that occurred in the past. We test this hypothesis by examining species-richness patterns of the land snail fauna on an oceanic island where forest was once destroyed but subsequently recovered.Location Hahajima Island of the Ogasawara Islands in the western Pacific.Methods Species richness of land snails was examined in 217 0.25 · 0.25 km squares during 1990-91 and 2005-07. Associations of species richness with elevation, current habitat quality (proportion of habitat composed of indigenous trees and uncultivated areas), number of alien snail species, and proportion of forest loss before 1945 in each area were examined using a randomization test and simultaneous autoregressive (SAR) models. Extinctions in each area and on the entire island were detected by comparing 2005-07 records with 1990-91 records and previously published records from surveys in 1987-91 and 1901-07. The association of species extinction with snail ecotype and the above environmental factors was examined using a spatial generalized linear mixed model (GLMM). ResultsThe level of habitat loss before 1945 explained the greatest proportion of variation in the geographical patterns of species richness. Current species richness was positively correlated with elevation in the arboreal species, whereas it was negatively correlated with elevation in the ground-dwelling species. However, no or a positive correlation was found between elevation and richness of the grounddwelling species in 1987-91. The change of the association with elevation in the ground-dwelling species was caused by greater recent extinction at higher elevation, possibly as a result of predation by malacophagous flatworms. In contrast, very minor extinction levels have occurred in arboreal species since 1987-91, and their original patterns have remained unaltered, mainly because flatworms do not climb trees. Main conclusionsThe species-richness patterns of the land snails on Hahajima Island are mosaics shaped by extinction resulting from habitat loss more than 60 years ago, recent selective extinction, and original faunal patterns. The effects of habitat destruction have remained long after habitat recovery. Different factors have operated during different periods and at different time-scales. These findings suggest that historical processes should be taken into account when considering local-scale diversity patterns.

Landscape history, time lags and drivers of change: urban natural grassland remnants in Potchefstroom, South Africa

“…Time lags occur because processes operating in landscapes take time, relict species can remain in altered landscapes, movements across the landscape may be slow, some biological events require certain rare concurrent conditions to take place, and time lags can be accumulated by a sequence of events (Magnuson 1990). Species respond in different ways to disturbances based on their life history characteristics (Ewers and Didham 2006;Chiba et al 2009;Kuussaari et al 2009), therefore, observed time lags vary. In vegetation, longer living trees show longer time lags than grassland and herbaceous plants (Davis 1986).…”

Application of Earth Observation Technology to Site Selection and Development of Ecotourism Management Plans in Rural Ghana

“…ese changes in forest landscapes oen affect both the structure and function of forest ecosystems thereby causing stochastic �uctuation of reduced animal and plant populations [20][21][22]. Habitat loss negatively affects species richness which is a salient attraction for tourists [23]. As a result, strategies for halting the decline must be clearly outlined in the management plans.…”

Impacts of introduced species on the biota of an oceanic archipelago: the relative importance of competitive and trophic interactions

“…Disturbance by introduced species (e.g., disturbance of seabird colonies by goats) is an important factor leading to the local extinction of native species ). Other factors can also affect local extinction of and/or declines in native organisms; e.g., habitat destruction by human activities affects native biota (Shimizu 2003;Toyoda 2003;Chiba et al 2009). These impacts were not included in this survey.…”

“…Although P. manokwari has not invaded most of the Ogasawara Islands (Kawakatsu et al 1999), other snail-eating flatworm species (e.g., unidentified species of the genus Bipalium) have invaded many parts of the islands (Okochi et al 2004). Field experiment and distribution studies have indicated that these snail-eating flatworms have also reduced native land snail numbers (Okochi et al 2004;Chiba et al 2009). Furthermore, the introduced black rat, Rattus rattus, reportedly preys on land snails (Chiba , 2010a.…”