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The effects of grazing by sheep at a stocking density of c. 1 sheep ha-1 from August to April on total vegetation cover, diversity of plant species, above-ground plant biomass and concentration of crude protein, neutral-detergent fibre and acid-detergent fibre of salt-marsh vegetation was assessed over a 2-year period on a newly created salt-marsh area on the Belgian coast. Assessments were made in both grazed and ungrazed areas in four elevation zones: low, intermediate, high and floodmark zone. The cover of dominant salt-marsh species (Salicornia europaea, Limonium vulgare and Elymus athericus), plant diversity, plant biomass and chemical composition of herbage were compared between grazed and ungrazed plots, and between 2005 (initial state) and 2007 (after a 2-year grazing period) using paired t-tests. Grazing by sheep maintained plant diversity in the high zone, whereas diversity decreased in the ungrazed plots. Grazing had no apparent effect on total vegetation cover and composition of the vegetation. Concentration of crude protein in herbage increased and that of neutral-detergent fibre decreased in the high and intermediate zones. Expansion of the dominant species of the high zone, E. athericus, was not affected by the stocking density used in the study.

Seed bank density and similarity between above-ground vegetation and seed bank with depth were compared between two adjacent salt marshes that differ in age. In addition, the effect of salinity on the variation in seed bank density and similarity between above-ground vegetation and seed bank with depth was compared between euhaline against mesohaline conditions in three salt marshes.Ten plots of 2 m×2 m were situated in a new salt marsh (existing since 2002) and 80 plots in three old salt marshes. Soil samples were collected at three different depths (0–5, 5–10, 10–15 cm) in spring 2006. Soil seed bank was investigated in germination experiments under greenhouse conditions. Germination experiments lasted 6 months and all seedlings were identified and removed after identification. Above-ground vegetation composition was determined during the growing season in all plots.Viable seed density was calculated for each plot and for the three different depths; the similarity between seed bank and floristic composition of the above-ground vegetation was calculated. A general linear model was used to investigate the effect of soil depth, salinity and age of the salt marsh on density and similarity between seed bank and above-ground vegetation.The results showed that seed density decreased with depth in all salt marshes, irrespective of their age and soil salinity. Seed density and similarity between seed bank and above-ground vegetation were higher in the new salt marsh than in the old one in the same study area. This is because in young as well as in old successional stages, the seed bank was mostly composed of new colonizers, while most perennial species were absent from the soil seed bank, although they were dominant in the standing vegetation of the old salt marsh.The characteristics of the seed bank of a mesohaline salt marsh were found not to be fundamentally different from that of both euhaline salt marshes.

The effect of inundation frequency on plant community composition, species turnover, total and growth form cover, species richness and abundance of individual common species was investigated. The study area was a newly created salt-marsh located along the Belgian coast with a more or less continuous gradient of inundation frequencies from 0.01% of all high waters for highest elevations to 100% for lowest elevations. Cover of all plant species was estimated in 119 permanent 2m × 2m plots along six randomly chosen transects perpendicular to the main inundation gradient with a 3m distance between the plots in 2003, 2005 and 2007. Detrended correspondence analysis (DCA) scores were used as a proxy for plant composition. Total cover, the cover of annuals and perennials, total species richness, species richness of annuals and perennials and species turnover was calculated for each plot. Repeated measurements and LSD were used to compare all variables in three different years for different inundation frequencies. In addition, TWINSPAN was used to distinguish plant communities in different years.The results showed that plant composition changed differently according to inundation frequency. The cover of annual species increased at a higher pace at higher inundation frequencies. The cover of perennials increased at higher pace at lower inundation frequencies. In total, species richness and the abundance of most species increased in time, indicating absence of a competitive exclusion among species. Nevertheless, the abundance and frequency of Atriplex spp., Chenopodium spp. and Salsola kali strongly decreased in time, indicating a declining natural succession. It seems that perennial species (e.g. Elymus athericus) are spreading by vegetative propagules from upward to downward. Frequent inundations hampered plant species turnover, because of the low number of species that can tolerate that environmental condition. The frequencies of communities dominated by Elymus athericus and Salicornia procumbens strongly increased in time, indicating that these species are getting more and more spatially separated, leading to a stronger separation of plant communities and an appearance of a salt-marsh zonation.

It is generally accepted that in terrestrial ecosystems the occurrence and abundance of plant species in late succession stages can be well predicted from prevailing soil conditions whereas in early succession their presence is much more influenced by chance events (e.g. propagule availability). In other words late successional vegetation stages would be deterministically structured, while early succession stages would be of a more stochastic nature.To test this hypothesis, we compared the effect of abiotic environmental factors on vegetation composition and probability of occurrence of single species in two adjacent saltmarshes, differing in age (successional stage). A new salt-marsh of about 14ha was created in 2002 by removing a several meters thick layer of sand and slurry which was deposited on the major part of the salt-marsh along the IJzer estuary in the 1960s. From 2002 onwards, primary colonization started on that sterile substrate by hydrochoric seed dispersal, induced by tidal water currents from an adjacent 4ha old salt-marsh and the latter remained untouched as saltmarsh for more than two hundred years. Between mid August and the end of September 2005, three years after the start of the colonization in the new salt-marsh, vegetation and three abiotic environmental factors (soil texture, salinity and elevation) were described in a set of 155 plots (2m × 2m), distributed over the new and the old salt-marsh.In contrast to the general rule for terrestrial ecosystems, the vegetation composition of the early succession stage of the new salt-marsh appears to be at least as much determined by the combined effect of the measured abiotic factors as that of the old salt-marsh. As revealed by logistic regression the presence/absence of perennial species as well as annual species of the young salt-marsh can be well predicted by the measured abiotic environment. For the old salt-marsh, this also holds for the perennials, but not for the annuals. The stochastic appearance of gaps in the perennial vegetation cover appears to be important for the establishment of annuals in the older salt-marsh.

In this paper, the effect of three winter seasons of sheep grazing on cover, composition and species richness of vegetation, Elymus athericus expansion and forage quality of saltmarsh species were studied. Four zones were selected: three in real salt-marsh habitat (low, intermediate and high levels) and the fourth in the transition between salt-marsh and sand dune habitat. In each of the three salt-marsh zones, one site was selected and two sites were designated in the transitional zone. Half of each site was excluded from grazing (so-called exclosures) all year round, while the other half was accessible to sheep from mid-August until mid-June (enclosure areas). At each zone, 10 plots (2m × 2m) were established: five within exclosure and five within enclosure sites. In all plots, the cover of all species was estimated in the growing season in 2005 (initial state) and 2007 (state after two years of grazing). In addition, a total of 1516 quadrates (50cm × 50cm) were used to harvest the biomass of species to estimate the forage quality variation during the grazing period inside the plots. The forage quality variables were the percentages of crude protein, acid detergent fibre and neutral detergent fibre. The data of the cover of dominant salt-marsh species, species richness, total cover, plant composition and forage quality parameters are compared between exclosure and enclosure plots and between two sampling years (2005 and 2007) using repeated measurements (general linear model) separately for each zone. The results showed that after three years of plant succession, sheep grazing had a positive influence on plant richness on the high part of the salt-marsh, a negative effect in the transitional zone and no effect in the other zones. Grazing had no effect on cover and plant composition. Forage quality parameters were affected by sheep grazing only in the low salt-marsh zone. Limonium vulgare had the highest forage quality andElymus athericus had the lowest. It would appear that grazing with the current intensity and number of grazers would fail to hamper the expansion of Elymus athericus. A higher intensity of mixed sheep-cattle or cattle grazing would be needed to better control this highly prolific species.

Seed bank density and similarity between seed bank and above-ground vegetation along depth were compared between two salt-marshes different in age. In addition, the effect of salinity on the variation in seed bank density and similarity between seed bank and aboveground vegetation along depth was investigated. The study was conducted in an euhaline saltmarsh that contained both old and newly created habitats. In addition, two other old saltmarshes were selected to study the effect of salinity on the distribution pattern of seed bank and similarity between seed bank and above-ground vegetation at different soil depths. One of them was mesohaline, the other euhaline.Ten plots of 2m × 2m were situated in the new salt-marsh (existing since 2002) and 80 plots in the three old salt-marshes. Soil samples were collected at three different depths (0- 5cm, 5-10cm and 10-15cm) in spring 2006. After washing by fresh water, the soil samples were spread in the greenhouse to allow viable seeds to germinate. Germination experiments lasted 6 months and all seedlings were identified and removed after identification. Aboveground vegetation composition was determined during the growing season in all plots. Viable seed density was calculated for each plot and for the three different depths; the similarity between seed bank and floristic composition of the above-ground vegetation was calculated. A general linear model was used to investigate the effect of soil depth, age and salinity of the salt-marsh on density and similarity between seed bank and above-ground vegetation.The results showed that seed density decreased with depth in all salt-marshes irrespective of their age and soil salinity. Seed density and similarity between seed bank and above-ground vegetation were higher in the new salt-marsh than in the old one in the same study area. This is because in young as well as in old successional stages, the seed bank was mostly composed of new colonizers, while most perennial species were absent from the soil seed bank, although they were dominant in the above-ground vegetation of the old salt-marsh.The characteristics of the seed bank of a mesohaline salt-marsh were found not to be fundamentally different from that of both euhaline salt-marshes.

This paper provides a comprehensive overview of the available knowledge on sedimentology and hydrodynamics and five major ecosystem components - microphytobenthos, vascular plants, terrestrial arthropods, zoobenthos (macrobenthos, meiobenthos, hyperbenthos and epibenthos) and avifauna - of Belgian sandy beaches (from foredunes to foreshore). An ecosystem overview is presented for this specific geographically delimited shoreline, instead of dealing with a single component only. Belgian beaches are (ultra-)dissipative, macrotidal and wide beaches with a cross-shore average median grain size of 160-380 μm. Sediment becomes coarser, slopes steeper, tidal range smaller towards the east. Especially eastern beaches have been reshaped frequently through human action (e.g. beach nourishment). Belgian beaches are characterised by the presence of highly adapted organisms. It is demonstrated that even a highly recreational and heavily populated coastline like the Belgian coast provides valuable yet threatened habitats to several beach-dependent species, which may reach high numbers. Vascular plants of the drift line, dry beach and embryonic dunes are mostly short-lived and thalassochorous. Most common species are sea rocket (Cakile maritima), prickly saltwort (Salsola kali subsp. kali) and sea sandwort (Honckenya peploides). Terrestrial arthropods inhabiting the same general area are highly diverse, comprising halobiontic, halophilous and haloxene species. Prominent members of this fauna are sandhopper (Talitrus saltator) and dipterans (flies). Microphytobenthos is an important primary producer on Belgian beaches, mainly consisting of diatoms. Very little is known about this group of organisms. Belgian beaches also have a specific zoobenthic fauna in both meiofauna and macrofauna, e.g. the typical upper intertidal Scolelepis squamata-Eurydice pulchra community. Also epi- and hyperbenthic animals depend on the beach, e.g. as nursery grounds. Nowadays no nesting of birds occurs on the beach itself. Nevertheless, Belgian beaches are important for resting and foraging (e.g. sanderling Calidris alba). Little is know about biological interactions on Belgian beaches. Human actions associated with several aspects of recreation, beach management and fisheries, are endangering all the discussed biota, and are specified.

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.

We monitored the spider and ground beetle assemblages of old dune and newly created dune-like habitats in the Ijzer estuary by means of four years of continuous pitfall sampling (2001-2004). The new sites built with dune sand were rapidly colonised by good dispersing species. These populations thrived so well during the first years after colonisation that they acted as sources, for which the old dune habitats were the sinks. That temporal collateral effect of nature restoration did not seem to cause persisting damage in the old dune habitats once the source populations had disappeared.Because general stochastic environmental fluctuations, like cold winters, seem to cause important year-to-year variation in population size of a number of species, it is advisable to sample developing and restoring habitats at the same time as their targets.The newly created habitats appeared to offer opportunities to enlarge the population size of several species of dune living ground beetles and, to a lesser degree, spiders. A multitude of more specialized dune species could not (as yet?) install viable new populations. A continuing sampling effort will be required to monitor the development, so that additional nature restoration or management measures can be taken when bio-indicated to be needed.

Populations of ground beetles and spiders are continuously monitored since 1990 in the dunes and salt marshes of the river Ijzer estuary (Belgium), where a recent nature restoration project took place within the framework of LIFE. Immediately after restoration measures, continuous (year cycle) pitfall and window trapping was performed during several years in restored or newly developed salt marsh and dune slack habitats and compared to target ('old' salt marsh) habitats. In this paper, we focus on ground beetle assemblages and species quality from these samplings, based on some 40,000 beetles identified to 96 species. Results show several beetles new to the study area as well as a marked increase of several target species with high conservation interest (Red-list species). However, many of these species could be rapidly lost again unless natural dynamic processes are kept ongoing. Historical beetle data show that many species that disappeared from the area during the past century have not yet been able to recolonise. This is especially true for salt marsh species and possibly due to dispersal limitation. Many dune slack species re-appeared but did not establish viable populations. Moreover, several ground beetle species indicate increased sand instead of silt deposits in new and old salt marshes. Further invertebrate monitoring therefore is a prerequisite for a well-founded long-term evaluation of the executed nature development measures. Such monitoring will be of much interest, both for an evidence-based nature conservation management, for fundamental ecological research, but also as a possible early warning system for the need of additional management measures in the future.

In order to evaluate recent nature development measures, ground beetles and spiders were studied in the river IJzer estuary (Belgium), an area that has been studied for these invertebrates without interruption since 1989. Starting immediately after restoration measures, five intensive short-term pitfall trapping campaigns were performed in 2001 till 2003 along nine transects covering the entire nature reserve. About 25.000 ground beetles and spiders were identified from more than 200 species. Assemblages, derived from these sampling campaigns, are compared between old and new habitats and sites and show quick species responses in the first years after the nature restoration measures. We observe several beetles and spiders new to the study area as well as a marked increase within the area of several target species with high conservation interest (Red data book species). However, beetle and spider results also suggest that additional management measures will probably be necessary for a further successful development of the nature restoration area. These mainly concern problems related to the maintenance of early successional dynamic stages of great biological value as well as those related to recently observed increased sand deposits in new and old salt marshes. Further invertebrate monitoring, including population genetics, therefore is a pre-requisite for a well-founded long-term evaluation of the performed nature development measures. Such monitoring will be of much interest, both for an evidence based nature conservation management and for fundamental ecological research.

1. In fragmented landscapes where natural disturbance acts at the local level, community composition can be altered either by 'species-by-species matching', with community-wide character displacement, or by 'constrained species sorting', whereby disturbance favours species with distinct ecological traits. It is necessary to understand such species shifts when aiming to detect bottlenecks associated with changing disturbance dynamics at different spatial levels. Such an understanding also provides insight into the underlying ecological mechanisms in operation and allows identification of species of conservation concern.2. This approach to understanding species' shifts was applied to a study of spider diversity and life-history variation in relation to sand dynamics in stabilized and dynamic grey dune landscapes located along the coasts of France, Belgium and the Netherlands.3. Local (alpha) diversity appeared to decrease with increasing local sand dynamics in both stable and dynamic landscapes. In dynamic dune landscapes, beta-diversity decreased significantly and approached regional (gamma) diversity under local grey dune stabilization; in stabilized landscapes, beta-diversity was not affected by local sand dynamics.4. Comparative analyses of ecological traits revealed shifts in life-history patterns, suggesting that patterns in local diversity resulted from species sorting. Species from fragments characterized by high sand dynamics showed narrower niche breadths, larger body sizes and longer generation times, while summer-active species tended to become residential after sand stabilization. This provides evidence for constrained species sorting in which natural disturbance (through local sand dynamics) allows only species with distinct ecological traits to persist.5. Synthesis and applications. Species with larger body sizes, longer generation times and a higher degree of habitat specialization (i.e. related to dispersal ability) would be expected to be more vulnerable at dynamic sites and more prone to extinction than their counterparts from stabilized fragments. In particular, species with a burrowing lifestyle would be expected to go extinct locally as a result of increasing soil development and soil hardness. Shifts in species composition were found to be more pronounced in dynamic landscapes. Hence ensuring conservation of sand dynamics at a landscape level rather than at a local level is of prime importance when aiming to conserve typical psammophilous spider species within local assemblages in grey dune habitats.

Beaches belong to the least studied ecosystems, although they contain typical habitats for a large amount of specialised terrestrial invertebrates. This specific beach fauna was quite diverse along the Belgian coast at the beginning of the twentieth century. Especially species bound to organic matter, washed up on the tide line, were well represented. As a result of the development of mass tourism, most of our beaches are subject to mechanical beach cleaning and the suppletion of sand. These activities are believed to be responsible for the degradation of the original habitat. However, documentation on this topic was scarce and evidence of negative effects on local biodiversity was lacking. Therefore, the main goal of this research was to make an inventory of the terrestrial arthropod fauna on Flemish beaches and analysing temporal and spatial variation, in function of abiotic components such as the degree of recreation and the intensity of mechanical beach cleaning. The main conclusion is that a high degree of recreation and mechanical beach cleaning indeed has a negative influence on the richness of the species bound to organic detritus and also induces a change in community structure of terrestrial invertebrates along the Flemish coast. Secondly, predators and even parasites are also indirectly influenced by these anthropogenic disturbances, as a result of the declining prey population. Excluding or at least reducing these impacts along certain sections of the Flemish coast, might ensure the preservation of the organic detritus on the tide line and hence its associated beach fauna.

Though often regarded as biological deserts, sandy beaches provide a unique habitat for several species. Research was conducted by a consortium of experts with as a first objective to provide an integrated overview of the Belgian beach ecosystem and all its major components. A second objective comprised a review of available literature on the ecological impact of beach nourishment. To meet the first objective, an integrated overview of the Belgian sandy beach ecosystem based on spatial and temporal variation of fauna and flora of 11 sandy beaches is provided. The presented results corroborate the overlooked ecological significance of sandy beaches as a habitat. Besides sedimentology and hydrodynamics, five ecosystem components were taken into account: microphytobenthos, vascular plants, terrestrial arthropods, zoobenthos and avifauna. Nourishment of beaches is a large scale anthropogenic influence on sandy beach ecosystem. Sandy beaches are regarded as systems with a strong resilience towards such impacts. Nevertheless serious (short term) ecological effects can be expected. A review of prior studies indicates that the impact of nourishment is rather case-specific and that it is difficult to draw general conclusions. Short term impact is mostly large due to total mortality of benthic life. It seems very likely that potential recovery from the impact of nourishment will be limited to two essential, species specific pathways: (1) survival by resident organisms and (2) re-colonisation by immigrating individuals, the latter depending on both the dispersal capacities and habitat demands of the organisms. Further research is needed to explore possibilities for reducing detrimental ecological effects. Specific studies are needed towards the survival options, the dispersal capacities and habitat demands of the species present. These should allow for management guidelines to be drawn in terms of preferable nourishment sediment characteristics, timing and practice of the deposition of the sand.

Since 1990, populations of ground beetles and spiders are continuously monitored in the coastal dune and saltmarsh habitats of the Yser Estuary (Nieuwpoort), within the context of a long-term study on invertebrate diversity, population dynamics and ecological and genetic effects of habitat fragmentation. By now, we know in detail the faunal composition of practically all available habitats in the study area. This is an ideal framework to monitor the effects of the nature development activities that started in 2001 in the area. Results of five large sampling campaigns in 2001-2003 (more than 25.000 carabid beetles and spiders, 218 species) show a number of new ground beetle and spider species and assemblages, but warrant that many of these could be rapidly lost again.

During the summer of 2001, we conducted a study on the spatial distribution of ants in coastal grey dunes (Oostduinkerke, Western Flanders, Belgium). Nest locations of the most abundant ant species were analysed with multivariate techniques. Tetramorium caespitum frequented moss-dominated vegetation, whereas Myrmica sabuleti, M. scabrinodis, Lasius flavus and L. meridionalis preferred grassy vegetations. Formica cunicularia and L. psammophilus occurred in all types of grey dune vegetation. According to recent literature, a positive spatial relationship can exist between the positioning of ant nests and the location of the myrmecochorous plants Viola curtisii, Luzula campestris and Polygala vulgaris in coastal dunes. Neither preliminary investigations, nor our study could confirm this significant positive relationship: the occurrence of myrmecochorous plants seems to be independent of the proximity of nests. It is possible that relationships are masked by a high turnover rate of the nest sites or by a restricted seedling establishment. We did not, however, observe ants transporting seeds of Viola, Luzula or Polygala in the field, possibly indicating the inefficiency of searching for those seeds in areas where population densities of these plants are rather low and other food sources are abundantly available.

We recorded the association between the planthopper Tettigometra laetus Herrich-Schäffer, 1835 (Hemiptera: Fulgoromorpha Tettigometridae) and three ant species belonging to the subfamilies Myrmicinae and Formicinae in a coastal dune area of Flanders (Belgium). Lasius psammophilus Seifert, Tetramorium caespitum L. and Formica cunicularia Latreille were observed attending and palpating the dorsal glandular area of this planthopper, taking honeydew directly from its anus, herding them and carrying them into their nests when disturbed. The planthopper was rarely found in the absence of ants and probably develops within ant nests, which may provide protection against predation and adverse weather conditions. The natural history of temperate ant-hemipteran relationships is discussed.

In this contribution we review which species richness estimators can be used if spiders are sampled with pitfall traps or other relative sampling methods. Due to the inherent bias typical for activity-based traps, only sample-based estimators were useful (Chao2, ICE and two jackknifing estimates). We estimated species richness for spiders from our four fragmented coastal dune habitats: dense and short grasslands, moss dunes and marram dunes. As extrapolation of the collector curve is only appropiate if the curve reaches a ceiling (asymptotic, such as parabolic and hyperbolic models), total species richness could not be determined by extrapolation in either of the investigated habitats. Because of the log-linear nature of the curves, non-parametric methods were applied. An absolute estimate of total habitat species richness was thus difficult to calculate; differences in total regional species richness could be analysed by comparing the different non-parametric estimator curves. If only habitat specific species were taken into account (we analysed this for grey dune habitats), extrapolation of the collector curve was appropiate (hyperbolic models). A relatively low number of traps were already enough for sampling more than 95% of the specific species. Estimates of the richness of specific species from grey dune patches (in contrast to species richness of the habitat) could already be derived from five traps. Our data revealed that grassland habitats were characterised by higher spider richness than moss-dominated grey dunes and that the latter were more diverse than Marram dunes. The number of specific species was slightly, although non-significantly, larger in dune grasslands than in moss-dominated dunes.

The crab spider Xysticus sabulosus (HAHN, 1832) is a sit-and-wait predator, typical for sandy habitats in Europe and Flanders. In the Flemish coastal dunes, the species is very abundant in grey and blond dunes. lts abdominal and cephalothorical colour varies from almost completely white to dark brown. During autumn 2001, we investigated crypsis as a function ofthe occupied micro- and macrohabitat. Our results indicate that (1) Colouration differs between the populations. The species is darker in a grey dune completely covered with dried (brown) mosses and in a humid dune slack covered with algae, than in populations from a sea inlet and from a blond dune. The colouration of a population from a grey dune with mosses, lichens and bare sand is intermediate. (2) Individual cephalothoracal colouration is, in contrast to abdominal colouration, related to microhabitat selection: individuals with darker cephalothoraxes occupy hunting sites with a higher coverage of mosses, while those with a pale one are found in microhabitats with a high amount of nude sand. The observed spider colour-environment covariation between populations is probably the result of natural selection or colour alteration during the juvenile development. Further research on these possible underlying mechanisms remains, however, necessary.

During this lecture, we present the results of a detailed study on the occurrence and ecology of spiders in the Flemish coastal dunes, as a tool for evaluating the conservation importance of dune arthropod species in general. Spider diversity is evaluated in function of the different assemblages, which are habitat specific. Especially dune grasslands, dune slacks and Marram dunes represent the highest value for nature conservation because of the presence of dune characteristic and dune specific species. These habitats are now heavily fragmented because of grass- and scrub encroachment. This fragmentation results in decreasing habitat surfaces, which affect the diversity and assemblage stability negatively. Habitat fragmentation not only affects the species diversity, but can also influence the viability of population. Within this framework we present the results of research on the effects of grassland fragmentation on the population dynamics, genetics and viability of our model species Pardosa monticola. Our results indicate that arthropod (spider) conservation will not only depend on the conservation of suitable habitat but also on the general landscape configuration.

El Niño is a worldwide climatological event occurring every 2 to 8.5 years. This event is associated with high sea-surface temperatures across the tropical Pacific and weak or reversing easterly trade winds. The combination of both leads to abnormally strong convective storms in the eastern Pacific and heavy rainfall in western Latin America (especially Ecuador and Peru) and in the Galápagos. The authors had the opportunity to witness the recent 1997-1998 El Niño event during their stay in the Galápagos in March and April 1998. The effect of extremely wet conditions upon the Hogna albemarlensis populations of the islands Santa Cruz, Santiago and Volcán Cero Azul (Island Isabela) were observed. Hogna albemarlensis, a coastal species, normally lives in saline habitats near lagoons and in permanent wetlands below 600m of altitude. It exhibited an extremely aggressive expansion of its distribution all over the islands and volcanoes, occurring everywhere in very high densities and even outnumbering the highland species Hogna galapagoensis which presumably evolved from the founder species H. albemarlensis. A situation was created in which both the coastal and the highland species, met each other for a certain period of time. Every El Niño event is followed by a number of extremely dry years (called La Niña) resulting in the drying out of all temporary wetlands produced during the El Niño period and once again restricting the lycosid populations to their former areas. El Niños have certainly played an important role in the speciation of the lycosid species on islands where the coastal species and highland species occur. A hypothesis is proposed.

Pardosa monticola (Araneae, Lycosidae) is a rare spider in Flanders. It is restricted to thermophilic mesotrophic (dune and heath) grasslands. Its life cycle and its habitat preference in the coastal dunes were analysed by interpreting data of more than 200 year-round pitfall-samplings. Viable populations are found in short dune grasslands (grazed by rabbits) and in mown young dune slacks. The life cycle is mixed annual-biannual and hibernation takes place in the juvenile or sub-adult instars. In short grasslands, the species overwinters in the rough neighbouring vegetation, in dune slacks, in litter accumulations. In the latter, the species survives submerging during winter inundation. Dispersal between suitable habitats can occur by male terrestrial movements via xerophylic habitats and dense grassland vegetation. Aeronautic dispersal is a rare phenomenon in the first instars that takes place only in periods of food shortage. Although a low proportion of the population exhibits this behaviour, this kind of dispersal can be of great importance for gene exchange between distant or strongly isolated populations. The implications and the importance of these data are discussed in relation to contemporary nature management.

A comparison is made between the spider species composition of twelve sandy natural areas in Flanders along a gradient from the coast dunes and salt marshes in the west to the large heathland areas in the east. All these natural areas have large numbers of rare and threatened species. The relative paucity in spider species in coastal reserves is caused by the lack of species bound to ombrotrophic Sphagnum bog vegetation and to wet oligotrophic grasslands.