L Baert

SPIDER ASSEMBLAGE STRUCTURE AND STABILITY IN A HETEROGENEOUS COASTAL DUNE SYSTEM (BELGIUM)

Abstract An analysis of the spider assemblage structure and the presence of indicator species in the Flemish coastal dunes are presented. The analysis is based on data from more than 170 year-round pitfall sampling campaigns from the 1970s onwards. We were able to find indicator species for all identified habitats. The assemblages are determined by variation in vegetation structure (succession), atmospheric and soil humidity and the occurrence of both natural of anthropogenic disturbance. In the fragmented habitats (grasslands and grey dunes), a clear relationship was found between the mean habitat size and the stability of the assemblage composition. In moss dominated dunes and short grasslands total species numbers do not increase with patch size. Due to microhabitat variation and the possibility of attaining viable population sizes the total number of typical species is, however, higher in larger patches. In small patches, edge effects are more important and the number of observed species is enlarged by the intrusion of species from nearby habitats.

Conservation on Volcán Alcedo (Galápagos): terrestrial invertebrates and the impact of introduced feral goats

Abstract Diversity, composition and community structure of terrestrial macroinvertebrates were compared along an altitudinal gradient on Volcan Alcedo (Isabela, Galapagos), sampled at nine sites in April 1986 and 1996. This volcano has recently suffered a population explosion of introduced feral goats, which have transformed large parts of the former forest and scrub into grassland, especially at higher elevations. Species diversity showed highest values for the lower arid part of the volcano with little change between 1986 and 1996. At higher elevations, diversity was generally lower, but the 1996 data revealed increased values compared with 1986. Species composition and relative abundance in samples from the lower arid and transition zones differed between periods, whereas at higher elevation this difference was masked by the effects of introduced goats. There was a decrease of high altitude specialist species (including several endemics) and a significant increase of more xerophilic species in overgrazed sites. Both the temporary increase in habitat heterogeneity and availability of dead wood explain the observed recent increase in species richness on goat-damaged sites. Firm and quick action to reduce the feral goat numbers could still restore the initial state and conserve most of the natural diversity of Volcan Alcedo.

Parallel habitat specialization within the wolf spider genus Hogna from the Galapagos

Within most island archipelagos, such as the Galápagos, similar ecological gradients are found on geographically isolated islands. Species radiations in response to these ecological gradients may follow different scenarios being (i) a single habitat specialization event followed by secondary colonization of each ecotype on the different islands or (ii) repeated and parallel habitat specialization on each island separately. This latter scenario has been considered less likely as gene flow might hamper such ecotypic differentiation. At least for the Galápagos, the extent to which this process is involved in species radiations remains yet poorly understood. Within the wolf spider genus Hogna, seven species are described that can be divided into three different ecotypes based on general morphology and habitat preference i.e. species that inhabit the pampa vegetation in the highlands, species that occur in coastal dry habitats and one generalist species. Comparison of the species phylogeny based on one mitochondrial (COI) and one nuclear (28S) gene fragment convincingly demonstrates that ‘pampa’ and ‘coastal dry’ species evolved in parallel on the islands Santa Cruz and San Cristóbal. Despite the observation that allozymes analysis indicated that each species forms a distinct genetic cluster, phylogenetic divergence within these species complexes was very low and paraphyletic and most likely due to hybridization rather than incomplete lineage sorting, as demonstrated for the Santa Cruz species complex. This suggests that within‐island speciation occurred under low levels of gene flow. Species phylogeny in general did not follow the progression of island emergence as a molecular clock analysis suggested that island endemic species may have diverged after as well as before the emergence of the islands. This represents the first clear example of parallel and within‐island speciation because of habitat specialization on the Galápagos and that such divergence most likely occurred under historic gene flow.

Spider communities of Isla Santa Cruz (Galapagos, Ecuador)

The various vegetation zones of the central Galapagoan island, Santa Cruz, have been sampled for spiders on three occasions, in 1982, 1986 and 1988. This paper deals with the synecological analyses (DECORANA, TWINSPAN) of the spider composition of the different vegetation zones of the island. There is an important varia- tion in the composition of the spider communities of Santa Cruz coinciding mainly with altitudinal variation. As for plants, this relationship is different for the northern as com- pared to the southern side. Only on the southern slope are there agricultural activities and human settlements. Although this has led to an increase in the spider faunal diversity, the balance for nature conservation has clearly to be interpreted as negative.

Cross-realm assessment of climate change impacts on species’ abundance trends

Climate change, land-use change, pollution and exploitation are among the main drivers of species’ population trends; however, their relative importance is much debated. We used a unique collection of over 1,000 local population time series in 22 communities across terrestrial, freshwater and marine realms within central Europe to compare the impacts of long-term temperature change and other environmental drivers from 1980 onwards. To disentangle different drivers, we related species’ population trends to species- and driver-specific attributes, such as temperature and habitat preference or pollution tolerance. We found a consistent impact of temperature change on the local abundances of terrestrial species. Populations of warm-dwelling species increased more than those of cold-dwelling species. In contrast, impacts of temperature change on aquatic species’ abundances were variable. Effects of temperature preference were more consistent in terrestrial communities than effects of habitat preference, suggesting that the impacts of temperature change have become widespread for recent changes in abundance within many terrestrial communities of central Europe.

Allozyme characterization of Hogna species (Araneae, Lycosidae) of the Galapagos Archipelago

Abstract The colonization of species on remote islands may result in phenotypic diversification and ultimately speciation. On the Galápagos Archipelago, seven very closely related morpho-species of the wolf spiders genus Hogna are distinguishable based on small somatic and genital differences. Based on habitat preference, these species can broadly be categorized into (i) three “high elevation species” occurring on the volcanic highlands, (ii) three “coastal dry” species occurring in dune habitats along the coast, and (iii) one generalist species which is chiefly found in wet coastal habitats such as salt marshes but also in wet habitats at higher altitudes. To determine the degree of reproductive isolation among these morpho-species, we investigated gene flow among populations and species based on nine allozyme loci. Genetic analysis by means of genetic distance estimates and cluster agglomerative analyses confirmed the status of the defined morpho-species. Allele frequencies were highly similar among populations within a species but differed profoundly among species. Genetic differentiation within the generalist species was generally very low. There were no constant differences between high elevation and coastal populations for this species. Neutral genetic divergence between species appeared to correspond more to geographic distribution rather than to a clear separation of the two different ecological groups within an island. This suggests that a parallel parapatric divergence between high elevation and coastal dry species may have taken place on the oldest islands of San Cristobal and Santa Cruz.

CALLEIDA MIGRATORIA CASALE, NEW SPECIES (COLEOPTERA: CARABIDAE), A NEWLY INTRODUCED GROUND BEETLE IN THE GALAPAGOS ISLANDS, ECUADOR

Abstract This contribution reports on the discovery of Calleida migratoria Casale, new species, a ground beetle previously unknown to the Galápagos Islands. Since the recent and very strong 1997–98 El Niño event we have found this species on five of the Galápagos Islands: Isabela, Pinta, Santa Cruz, Santiago and Rabida. The species is also known from Peru and its presence in Galápagos is therefore most probably another anthropogenic introduction which has taken advantage of the unusually favourable climatic circumstances of the last El Niño. Calleida migratoria is described and a provisional identification key is added to distinguish the new taxon from its closest relatives.

Importance of core and linear marsh elements for wetland arthropod diversity in an agricultural landscape

The importance of linear habitat elements connecting core habitat patches for biodiversity conservation is still poorly understood. We surveyed reed strips along drainage ditches and reed marshes in an agricultural landscape to assess how both the density of linear habitat elements and the area of core habitat affect diversity and community composition of spiders, ground beetles, and long‐legged flies. For each taxonomic group, species composition of both ‘all’ and ‘typical wetland’ species, but not species richness was different between ditches and marshes. Overall local species richness and richness of species of conservation interest were affected at a landscape scale both by the density of ditches and by the area of core wetland. Strength and direction of these effects differed among groups. An increase in the density of reed ditches positively affected the total species richness of spiders and ground beetles and the species richness of typical wetland ground beetles, but not for long‐legged flies and typical wetland spiders. The positive effects were explained by improved network functionality, rather than by increase in available habitat area at landscape level. The number of red list spiders and long‐legged flies increased only with increasing core wetland area, while no significant effects were found for the number of red list ground beetles. Our study revealed that preserving or increasing the density of habitat corridors (more reed ditches) can be beneficial for the species richness of particular predatory arthropods, including species of conservation concern (especially ground beetles). Other groups react indifferently or are only positively impacted by an increase of core wetland area.