Susceptibility of tropical mountain forests to biological invasions from the temperate and subtropical zone, exemplified by <i>Zonitoides</i> (Gastropoda: Gastrodontidae)

Colonisation by, and spread of, animal species from the temperate zone are rather uncommon observations in the tropics. The study provides the first reports of two snail species of the genus Zonitoides in Sabah, Borneo, namely Z. arboreus (Say, 1819) and Z. nitidus (O.F. Muller, 1774). The identification was aided using partial sequences of 28S rDNA, and the barcoding sequence of COI. So far, the two Zonitoides species were found in locations where the natural forest cover had been disturbed, and only in the montane forest at elevations between 1500 and 2000 m a.s.l.. Niche modeling suggests that both taxa could be widely distributed in the mountains of tropical South America and Africa. Z. arboreus finds suitable climates in many places in SE Asia and especially at many conservation areas in Borneo. In contrast, Z. nitidus finds only marginal climatic conditions in the same area, and introductions of Z. nitidus probably will remain spatially restricted. This prediction, however, needs to be monitored because the latter species can display molluscivory. Our results additionally point to the possibility of Z. arboreus being a species complex that, given its potential economic impact, urgently needs a taxonomic revision.</p

Responses of forest snail assemblages to soil acidity buffer system and liming

Physiological constraints from harsh environmental conditions, such as from calcium limitation on acidic soils, is expected not only to affect species richness, but also species abundance distributions. Also, the effects of amendments by calcium addition (soil liming) on these assemblage characteristics are poorly understood. Because of their sensitivity towards calcium availability, we use snails as model organisms and integrate field surveys and literature data. Temperate forest snail data supported a rule-of-thumb calibration with pH measurements in water being one unit higher than in KCl buffer. The resulting large data set suggests stepwise changes in snail richness that occur at transitions in soil buffer systems, especially at pH 3.2. Species abundance distributions follow the logseries model in most soil buffer systems, except for the iron buffer range (pH a parts per thousand currency sign3.2) where they swap to the geometric model. Our findings thus suggest several smaller soil pH thresholds for snail assemblages associated with shifts between soil buffer systems, and a tipping point at the threshold to pH a parts per thousand currency sign3.2. Liming with ground carbonate rocks is a technique to temporarily increase soil pH and calcium availability in forest soils, but its effects on snail assemblages produced inconsistent results that did not meet expectations from the ameliorated soil pH and might warrant a re-evaluation of liming applications

HABITAT EFFECTS ON SLUG ASSEMBLAGES AND INTRODUCED SPECIES

Habitat disturbance alters environmental conditions and can affect biotic exchange. While the process of biotic exchange is difficult to quantify in the field, it affects community assembly and thus species abundance distributions, diversity, faunal homogeneity and biogeographic patterns. Here, we provide the first comprehensive assessment of habitat-specific assemblage structure and turnover in slow, active dispersers, namely slugs (Mollusca: Gastropoda). We compare species richness, densities, assemblage homogeneity and spatial turnover from nine differently disturbed habitat types (total: 729 sites) within an area spanning the border between two major European biogeographic regions, the Atlantic and the Continental Regions. Gardens, mesic open habitats and successions tended to harbour many introduced species. The nonmetric multidimensional scaling plot revealed a gap, rather than a transition, between disturbed habitats (including woody successions) and mature forest stands. This gap indicates a tipping point for slug assemblages related to food sources and microclimate. Anthropogenic disturbance blurred the effect expected from the border between the biogeographic regions. When compared with broadleaved forests as the natural vegetation cover, human disturbance doubled the range before spatial faunal dissimilarity occurred in physically highly fragmented gardens, and more than tripled it in continuously-disturbed habitat types such as mesic open habitats. Our results support the idea that continuously-disturbed habitats are associated with altered passive dispersal and colonization dynamics, distorted biogeographic boundaries and faunal homogenization

On the Growth of Bivalve Gills Initiated From a Lobule-Producing Budding Zone

Volume: 205Start Page: 73End Page: 8

Differences in dispersal- and colonization-related traits between taxa from the freshwater and the terrestrial realm

The aquatic and terrestrial realms differ in many physical properties that not only require specific physiological adaptations but also cause differences in dispersal options. We thus expect that life-history traits related to dispersal and colonization are under selection pressure because freshwater habitats are more isolated and thus more difficult to reach. We compared traits from European databases of three taxonomic groups along the passive-active dispersal gradient: plants (Plantes), snails (Mollusca: Gastropoda: Prosobranchia et Pulmonata) and hoverflies (Diptera: Syrphidae), all of which have both terrestrial and freshwater species (plants and snails) or early life stages (hoverflies). Aquatic taxa seem to be more successful long-distance dispersers than are terrestrial taxa. Our analysis also revealed lower numbers of seeds or eggs produced in the aquatic habitats. However, aquatic taxa often allocate resources to offspring guarding (vegetative propagules in plants, egg capsules in snails) and breeding-site selection (syrphids). Colonization of the aquatic realm is reinforced by increases in life span (plants), clonal spread (plants), shorter generation times (snails), selfing ability (marginal effect in pulmonate snails) or paedogenesis (two incidences in hoverflies, needs further studies). Probably, the variety of strategies reflects the different evolutionary backgrounds that elicit different combinations of trade-offs, but all traits also might increase invasibility of species

INFLUENCE OF HABITAT STRUCTURE AND CONDITIONS IN FLOODPLAIN FORESTS ON MOLLUSC ASSEMBLAGES

Alder floodplain forests are a rare and threatened forest type in Europe. These forests can be very rich in mollusc species. The intermediate disturbance hypothesis predicts that species richness should peak at intermediate inundation frequency, that is, at intermediate elevation above the river level. We additionally hypothesized that constantly high soil moisture can distort the usually positive correlation between the amounts of downed deadwood and snail richness, and that tree stems might be more favourable than deadwood because their vertical structure provides a better refuge during inundation events. To this end, we sampled molluscs from a core area of 20 x 20 m from eight alluvial forests with black alder in the surroundings of Lodz, Central Poland. In each core area, substrate was collected from eight random plots (0.25 m(2) each). We also recorded soil pH, vascular plant species and mosses diversity, along with other structural variables. Plant indicator values were calculated according to Ellenberg. Soil quality (amongst others: soil pH, reactivity value, nutrient and moisture availability) decreased with increasing elevation above the river level. In the plot samples, we found a total of 18,497 individuals from 52 species. Mollusc species richness dropped stronger than densities with an increasing elevation above the river level Main influences on mollusc richness and abundance originated from positive correlations with soil pH and moisture. An additional hand sampling campaign on tree stems and deadwood items in the core area revealed that coarse woody debris items on average carried twice as many individuals as did tree stems. Deadwood and tree stems supported similar numbers of snail species per item, but beta-diversity was higher on deadwood. Consequently, Jackknife 2 predicted that deadwood is utilized by about 46 species, whereas tree stems only support about 39 species. Our results indicate (1) that mollusc richness peaks at low elevations above normal water level in this type of forest, (2) that intact hydrological regimes are associated with high soil quality and mollusc biodiversity, and (3) suggest that coarse woody debris adds resources, refuges and a dispersal agent for the alder forest floor fauna

Response of non-native European terrestrial gastropods to novel climates correlates with biogeographical and biological traits

Aim Anticipating the propensity of species to persist outside the climatic conditions in which they are observed is important in assessing the uncertainty in climate-matching when applied to different locations or times. By using data from 27 European terrestrial gastropods (slugs and snails) established in new regions, we measured (1) the degree of climate match between native and non-native ranges and (2) the diversity of novel climatic conditions inhabited. We then tested for species traits as predictors of the patterns found. Location Worldwide. Methods We projected the occurrences of each species onto the climatic space defined by the two main axes of a principal components analysis. On the basis of the convex hull of native occurrences, we measured the proportion of non-native occurrences in novel climates and the diversity of the newly occupied climates. Generalized estimating equations were used to test for associations between climatic responses and species traits, while considering phylogenetic relatedness and introduction effort. Results Approximately half of the species had a large proportion (> 25%) of non-native occurrences in novel climates. Climate mismatch was significantly higher for species with narrow native climatic niches, native ranges elongated in a north-south direction or native ranges with the southern limit at lower latitudes. Slugs occupied a higher diversity of novel climatic conditions than snails. Main conclusions Climate matching showed varying levels of accuracy in predicting the non-native ranges of the studied species. Lower accuracy appeared to be mainly related to low levels of distributional equilibrium in native ranges. In addition, coarse-scale predictions for species that are able to take advantage of microclimatic variability - as appears to be the case with slugs - may be challenging. We conclude that species traits can contribute to understanding uncertainties in climate-matching exercises