Kinship and food availability influence cannibalism tendency in early-instar wolf spiders (Araneae: Lycosidae)

For potentially cannibalistic animals such as spiders, the ability to recognize and avoid kin and/or preferentially cannibalize non-relatives would permit exploiting conspecifics as prey while minimizing loss of inclusive fitness. We investigated the effects of relatedness and availability of alternative food on cannibalism tendency in pairs of juvenile Hogna helluo (Walckenaer), a North American wolf spider (Araneae: Lycosidae). For second-instar spiderlings (dispersing stage), cannibalism was more likely among pairs of non-sibs than pairs of sibs and, interestingly, was also more likely when other prey were available. We found no evidence of increased cannibalism in pairings involving broods of greatest average size disparity, indicating that size differences are unlikely to explain differences in cannibalism tendency. Additionally, the relative number of deaths from cannibalism or other causes did not increase with increasing risk of starvation. For third-instar spiderlings, which had lived independently of their mother and sibs following dispersal, cannibalism rates were very high in all treatments and there were no significant effects of relatedness or food availability. Our results suggest that spiders with predominantly solitary lifestyles may bias cannibalism toward non-kin during the juvenile associative period, and that this effect is lost in the subsequent instar. Results are discussed in the context of several potential mechanisms that might result in differential cannibalism.Communicated by M. Elgar     

Factors influencing sexual cannibalism and its benefit to fecundity and offspring survival in the wolf spider Pardosa pseudoannulata (Araneae: Lycosidae)

Sexual cannibalism is hypothesized to have evolved as a way to obtain a high-quality meal, as an extreme mate choice or as a consequence of female aggressive spillover. Here, we examined underlying factors likely to influence sexual cannibalism in the wolf spider Pardosa pseudoannulata (Bösenberg & Strand, 1906) from China, including mating status, female egg-laid status, female hunger level, female adult age and mate size dimorphism. The results showed that about 10 % of P. pseudoannulata virgin females cannibalized the approaching males before mating and that 28 % of P. pseudoannulata virgin females immediately cannibalized the males after mating. No incidents of sexual cannibalism during copulation were observed. Before mating, previously mated females and starved females tended to engage in significantly higher rates of attacks compared to virgin and well-fed females. Females that had laid egg sacs tended to engage in a significantly higher rate of attacks and sexual cannibalism than virgin females before mating. Regardless of pre- or post-mating, there was a strong positive relationship between mate size dimorphism and the occurrence of sexual cannibalism. We also tested the effects of sexual cannibalism on the fecundity of cannibalistic females and the survival of their offspring. Our results indicated that sexual cannibalism affected positively the offspring survival of cannibalistic females, but not fecundity. Our findings support the hypothesis that sexual cannibalism has evolved as an adaptive component of female foraging strategy and that it benefits offspring survival as a result of paternal investment.     

Mate with the young, kill the old: reversed sexual cannibalism and male mate choice in the spider Micaria sociabilis (Araneae: Gnaphosidae)

Female mate choice is regarded as a strong selective force that significantly affects male mating success. In extreme cases, mate rejection can result in sexual cannibalism. However, males may choose between their partners as well. The killing of potential female mates, i.e. reversed form of sexual cannibalism, may be related to male mate choice. We examined male mate choice in the spider Micaria sociabilis, focusing on the roles of female mating status (virgin/mated), size and age. Reversed cannibalism reached its highest frequency in the period of generation overlap, i.e. when young males from the summer generation met old(er) females from the spring generation. These results suggest discrimination against old(er) females. The frequency of cannibalism was not affected by female mating status or female size. However, larger males from the summer generation were more cannibalistic than smaller males from the spring generation. We conclude that reversed sexual cannibalism might be an adaptive mate choice mechanism and can be explained in the context of the aggressive spillover hypothesis.     

Sexual cannibalism facilitates genital damage in <Emphasis Type="Italic">Argiope lobata</Emphasis> (Araneae: Araneidae)

Sperm competition is a potent driving force in evolution leading to a remarkable variety of male adaptations that prevent or reduce fertilization by rivals. An extraordinary defensive strategy against sperm competition has evolved in a number of web spiders where males break off parts of their paired genitalia in order to obstruct the copulatory openings of females (mating plug). A recent comparative analysis on the family level reports that genital damage is most frequent in species with sexual cannibalism although, as yet, a functional association between sexual cannibalism and genital damage has not been found. Using the moderately sexually cannibalistic orb-web spider Argiope lobata, we show for the first time that males cannibalized during their first copulation damaged their pedipalps with significantly higher probability (74%) than males that escaped (15%). Of all males that damaged their genitalia, 44% were able to place a genital fragment inside the copulatory opening of the female, resulting in a relatively low total plugging rate of 14%. Successful obstruction of the female copulatory opening reduced the share of paternity of subsequent males (P ₂ = 0.06%), thus, indicating that genital damage may have evolved as a response to sperm competition in this species as well. However, the low incidence of successful plugging and the strong relationship between sexual cannibalism and genital damage suggest that apart from paternity protection, the nature of genital damage in A. lobata is further shaped by sexual conflict or cryptic female choice.     

Fitness consequences of sexual cannibalism in female<Emphasis Type="Italic"> Argiope bruennichi</Emphasis>

The evolution of sexual cannibalism as the most extreme form of nuptial feeding is still poorly understood. Although increasing evidence suggests that female aggressiveness is related to other aspects of foraging behaviour, it is not clear whether the nutritional value of a male is sufficient to provide an adaptive significance for sexual cannibalism. A widely cited though rarely tested explanation is based on a paternal investment model, and predicts that consumption of a male results in increased female fecundity. The available evidence is either correlational or restricted to species with relatively large and potentially nutritious males, and different studies have come to different conclusions. Here we present a test of the paternal investment hypothesis using the very cannibalistic and highly size-dimorphic spider Argiope bruennichi. After a preset schedule, we had females consume none, one or two males independent of the female's cannibalistic behaviour. Consumption of male bodies did not result in any detectable fitness benefit for the female: neither the number of clutches, nor clutch size or hatching success were affected by consumption of males. The frequency of cannibalism was around 80%, independent of the female mating status. We did not observe male complicity, but cannibalism was associated with prolonged copulation. This suggests a sexually selected benefit of cannibalism for males. We conclude that the paternal investment hypothesis does not explain the existence of sexual cannibalism in A. bruennichi and probably not in other spider species with a pronounced sexual size dimorphism.Communicated by L. Simmons     

Kleptoparasites: a twofold cost of group living for the colonial spider, Metepeira incrassata (Araneae, Araneidae)

Several species of kleptoparasitic and araneophagic spiders (Araneae: Family Theridiidae, Subfamily Argyrodinae) are found in colonial webs of the orb-weaving spider Metepeira incrassata (Araneae, Araneidae) from Mexico, where they steal food and/or prey upon their spider hosts. Census data from natural M. incrassata colonies reveal that the incidence of these species increases with colony size. This pattern may reflect the presence of several other orb-weaving spiders, each with their own kleptoparasitic species, invading larger M. incrassata colonies. As the number of these associated spiders increases, so does the density and number of Argyrodinae species in M. incrassata colonies, suggesting that associated spiders might reduce their own kleptoparasite load by building their webs within M. incrassata colonies. This represents a twofold cost to M. incrassata, as a field enclosure experiment revealed that a primarily kleptoparasitic species (Argyrodes elevatus) may reduce prey available to their hosts, but a kleptoparasitic/araneophagic species (Neospintharus concisus) inflicts high mortality upon M. incrassata. However, the cost of kleptoparasitism and predation by these species may be offset in part for M. incrassata individuals in large colonies by certain defensive mechanisms inherent in groups, i.e., “attack-abatement” and “selfish herd” effects. We conclude that increased occurrence of kleptoparasitic and/or predatory Argyrodinae spiders is a consequence of colonial web building and is an important potential cost of group living for colonial web-building spiders.     

The behavioral ecology of cannibalism in cane toads (<Emphasis Type="Italic">Bufo marinus</Emphasis>)

Laboratory studies show that predatory cane toads (Bufo marinus) exhibit specialized toe-luring behavior that attracts smaller conspecifics, but field surveys of toad diet rarely record cannibalism. Our data resolve this paradox, showing that cannibalism is common under specific ecological conditions. In the wet–dry tropics of Australia, desiccation risk constrains recently metamorphosed toads to the edges of the natal pond. Juvenile toads large enough to consume their smaller conspecifics switch to a primarily cannibalistic diet (67% of prey biomass in stomachs of larger toads). Cannibalistic attack was triggered by prey movement, and (perhaps as an adaptive response to this threat) small (edible-sized) toads were virtually immobile at night (when cannibals were active). Smaller metamorphs were consumed more frequently than were larger conspecifics. The switch from insectivory to cannibalism reflects the high dry season densities of small conspecifics (in turn, due to desiccation-imposed constraints to dispersal) and the scarcity of alternative (insect) prey during dry weather. Our study pond (102 m in circumference) supported >400 juvenile toads, which consumed many metamorphs over the course of our study. Toads appear to be low-quality food items for other toads; in laboratory trials, juvenile toads that fed only on conspecifics grew less rapidly than those that ate an equivalent mass of insects. This effect was not due to parotoid gland toxins per se. Thus, cane toads switch to intensive cannibalism only when seasonal precipitation regimes increase encounter rates between large and small toads, while simultaneously reducing the availability of alternative prey.     

Influences of aggregative behaviour on space occupation in the spider Zygiella x-notata (Clerck)

Summary The distribution of the spider Zygiella x-notata was examined using field populations of adult females occupying the outside frames of windows. The structure of the populations was aggregative, and the distribution of individuals on the window frames and the size of the webs were density dependent. Also, the sizes of the webs of neighbouring spiders on the same window alternated. This spatial organization involves interactions between neighbours. If one spider out of two is removed, and if all the webs are destroyed, remaining spiders that previously had small webs significantly increase the size of their construction. In contrast, individuals that previously had large webs do not modify the size of their construction. This shows that individuals of Z. x-notata respond to the presence of neighbours. The influence of intraspecific interactions in such a population is discussed.     

Kin recognition by juvenile predatory mites: prior association or phenotype matching?

Kin recognition, the biased treatment of conspecific individuals based on genetic relatedness, is a widespread phenomenon in animals. The most common mechanisms mediating kin recognition are prior association (familiarity) and phenotype matching. Recognition based on prior association allows identifying familiar individuals. Recognition based on phenotype matching is an extension of prior-association-based recognition and allows identifying familiar and unfamiliar individuals due to a shared phenotypic trait. I investigated which of the two mechanisms is used by cannibalistic juvenile predatory mites, Phytoseiulus persimilis. Protonymphs that were associated with either siblings or non-kin discriminated familiar and unfamiliar larvae and preferentially cannibalized the latter irrespective of genetic relatedness. In contrast, despite previous association with either siblings or non-kin, protonymphs did not discriminate unfamiliar sibling and unfamiliar non-kin larvae. Association in the larval stage therefore mediated kin recognition based on familiarity, but not phenotype matching in cannibalistic P. persimilis protonymphs. Furthermore, in the presence of a familiar prey individual, sibling cannibalism occurred significantly sooner than non-kin cannibalism. This quick sibling cannibalism may have been the consequence of preferential association of siblings and/or may indicate the occurrence of an alternative cannibal phenotype. I discuss the adaptive significance of prior-association-based recognition for P. persimilis juveniles and emphasize the ability of P. persimilis to use multiple recognition mechanisms in dependence of the ontogeny and the ecological context.     

The selective advantages of cannibalism in a Neotropical mosquito

We investigated the benefits of larval cannibalism in the Neotropical mosquito Trichoprosopon digitatum. The clutch size of the mosquito in the field was strongly correlated with adult female size, indicating a fitness advantage to being large. In controlled laboratory experiments, we compared the survivorship and eventual adult sizes of larvae that were given the opportunity to cannibalise conspecifics throughout their lifetimes with the survivorship and adult sizes of larvae that were prevented from cannibalising. Since the benefits of cannibalism are likely to depend on the context in which it occurs, the experiment was conducted at two levels of alternative food availability. When food availability was high most larvae survived to adulthood, females cannibalised more than males and there was no measurable advantage to cannibalism in terms of survival rate, emergence time or adult size. Larvae were significantly more cannibalistic when food availability was lower, although under these conditions no larvae survived to adulthood. Nevertheless, under low food an important fitness benefit to cannibalism was revealed: individuals which had the opportunity to cannibalise survived significantly longer as larvae than those which did not. This increased longevity is likely to provide an important advantage to mosquito larvae when they wait for the input of unpredictable food sources. Received: 7 October 1995/Accepted after revision: 13 April 1996     

Females reward courtship by competing males in a cannibalistic spider

Despite widespread recognition that intersexual interactions shape reproductive strategies, studies of male competition do not typically include effects imposed by females. In cannibalistic redback spiders, escalated fighting between rival suitors is predicted, as males are unlikely to mate with more than one female, and strong first-male sperm precedence favours mating with virgins. In staged competitions for matings between size mismatched rivals, smaller males adopted an alternative sneaking strategy. However, despite initial agonistic interactions, larger males did not pursue or incapacitate smaller males. When inter-male competition occurred, females struck at males frequently, although strikes were rarely seen when males courted in the absence of a rival. After minimal fighting, larger males engaged in significant courtship (3 h) rather than killing inferior rivals. Prolonged courtship was favoured by female behaviour, as males that attempted rapid copulation (smaller, sneaking males) were cannibalised before mating was completed. This premature cannibalism significantly decreases paternity in redback spiders. Thus, significant features of male competitive behaviour (i.e. prolonged courtship by larger males) may be predicted with consideration of the female’s response to male reproductive strategies. Although the effect of females may be more subtle in systems without the extreme reversed size-dimorphism of redbacks, these results suggest that female interests should be explicitly considered when studying inter-male interactions.     

Precopulatory sexual cannibalism in fishing spiders (Dolomedes triton): a role for behavioral syndromes

Precopulatory sexual cannibalism (predation of a potential mate prior to copulation) offers an extreme example of intersexual conflict, a current focus in behavioral ecology. The aggressive-spillover hypothesis, posits that precopulatory sexual cannibalism may be a nonadaptive by-product of a general syndrome of voracity (aggression towards prey) that is expressed in multiple behavioral contexts. In this view, selection favoring high levels of voracity throughout ontogeny spills over to cause sexual cannibalism in adult females even when it is not necessarily beneficial. Using the North American fishing spider, Dolomedes triton, we present the first in depth test of this hypothesis. We found support for three aspects of the spillover hypothesis. First, voracity towards hetero-specific prey results in high feeding rates, large adult size, and increased fecundity. Second, juvenile and adult voracity are positively correlated (i.e., voracity is a consistent trait over ontogeny). Third, voracity towards hetero-specific prey is indeed positively correlated with precopulatory sexual cannibalism. Assays of antipredator behavior further revealed positive correlations between boldness towards predators, voracity and precopulatory sexual cannibalism. Overall, our results support the notion that precopulatory sexual cannibalism in D. triton is part of a behavioral syndrome spanning at least three major contexts: foraging, predator avoidance, and mating.     

Dispersal behaviour and colony structure in a colonial spider

Group living in spiders is characterised by two principle modes, the cooperative social mode and the colonial non-cooperative mode. Kin-relationships due to reduced dispersal determine population genetic structure in social spiders, but the dispersal mechanisms underlying group structure remain poorly understood in colonial spiders. Assuming similar ecological benefits of group living, we address the question whether reduced dispersal shapes population structure in a colonial spider, Cyrtophora citricola (Araneidae). We analysed dispersal by studying settling decisions under semi-natural conditions in experimental trees with and without colonies, and in natural populations, we estimated dispersal and colony structure using population genetic analyses. The propensity to disperse decreased with increasing age in experimental colonies. Adult females did not disperse in the experiment. Sub-adult female spiders preferred trees with a colony to trees without a colony. Dispersal in third instar juveniles was influenced significantly by wind but not by the presence of a colony. Thus, we showed that being in a colony did not inhibit juvenile dispersal, but pre-mating females were philopatric. Genetic differentiation among colonies in natural populations was heterogeneous, colonies being either little or highly differentiated. The heterogeneous structure is likely caused by colony founding by one or a few females followed by dispersal among perennial colonies. Gene flow, however, was slightly male-biased. The experimental and indirect, genetic approaches combined showed that dispersal and the breeding system of C. citricola resemble that of solitary spiders, with juvenile dispersal occurring in both sexes, while the colonial distribution is maintained by female philopatry.     

Initiation and resolution of jumping spider contests: roles for size, proximity, and early detection of rivals

Animals are commonly expected to assess each other during contests in order to economically identify relative status. Escalated or long contests are expected to arise mainly when rivals have difficulty discriminating small differences. Results of the present study of male-male contests in Plexippus paykulli, a jumping spider (Salticidae) with acute vision, are not in accord with this widely held view. Despite the typical finding that size-advantaged rivals are more likely to win contests and that this tendency increases with size disparity, contest dynamics suggest that these tendencies are achieved in the absence of direct size assessment. In contests between different-sized spiders, maximum escalation and overall duration were predicted by the absolute size of the size-disadvantaged spider (usually the loser) rather than the size difference between the rivals. This result suggests that spiders base decisions of persistence on their own size, such that size-disadvantaged rivals usually reach their limits first, and then retreat. This interpretation is further supported by findings that maximum escalation and total duration were both positively related to size in contests between size-matched spiders. Spiders were more likely to win if they oriented and displayed first, and longer, more escalated, contests ensued if the size-disadvantaged spider was the first to orient and display. Proximity of rivals at contest outset also influenced contest dynamics, but not outcome.     

The impact of grazing on spider communities in a mesophytic calcareous dune grassland

During 1994–1995 and 1997–1998 spiders were sampled with pitfall traps in a botanically rich, mesophytic, calcareous dune grassland in Belgium. As a consequence of intensive cattle grazing, vegetation variation in a large part of the area had diminished. The study area was also patchily grazed by rabbits. Community analysis with TWINSPAN revealed five distinct spider communities. Ecological differentiation was best explained by combination of the habitat variables: distance from grazed or non-grazed vegetation,Rosa pimpinellifolia cover and grass cover in both summer and winter. Species diversity was highest in the border zone between the cattle-grazed and non cattle-grazed sites. Correlation of the most abundant spider species with the vegetation determinants explains the ecological differentiation between the spider communities. Species were classified into seven major groups that reflect the species’ habitat preferences. The group showing clear association with non cattle-grazed, tall vegetation consists of common species. Characteristic species for the intensively cattle-grazed sites are common aeronauts and rare species such asWalckenaeria stylifrons, Mastigusa arietina, Ceratinopsis romana andPardosa monticola. The latter are shown to be dependent on ungrazed vegetation for juvenile development and overwintering. Intensive grazing results in homogeneous short vegetation, which can only be colonized by ‘open ground’ species with a well-developed dispersal capacity, or by species which are not dependent on litter-rich situations for juvenile development. An extensive cattle grazing regime results in a patchy mosaic grassland where, in addition to the above mentioned groups of species, other species survive by migrating between the buffered litter rich ungrazed vegetation and the short vegetation. Additionally, some typical and rare species prefer the transition zone between the grazed and the ungrazed vegetation because they are associated with specific habitat structures or inhabiting ant-species.     

Trade-off between pre- and postcopulatory sexual cannibalism in a wolf spider (Araneae,Lycosidae)

Sexual cannibalism can occur before, during or after mating. Relatively few experimental studies have examined why there is variation in the timing of sexual cannibalism. We examined the latency and number of attacks required for female spiders to capture male spiders pre- vs. postcopulation. We also examined the effects of female mating status and hunger level on the occurrence of pre- and postcopulatory cannibalism, which reflects the contribution of both relative capture success and female motivation to cannibalize males. Precopulatory cannibalism occurred after a shorter interval and required fewer chases and physical interactions for the female to successfully capture the male than was the case for postcopulatory cannibalism. Virgin females were more likely to engage in postcopulatory rather than precopulatory cannibalism and mated females vice versa. Those virgin females that did engage in precopulatory cannibalism had significantly lower body condition than virgin females engaging in postcopulatory cannibalism. While precopulatory cannibalism occurred more quickly and required fewer attacks by females, it comes at a potential cost of not mating with males. Hence, females are more likely to engage in precopulatory cannibalism if they have already mated or, if virgins, if they have low body condition. These results indicate that the decision of when to cannibalize males is dynamic and depends upon the relative value of a male as a mate versus a meal.     

Within-group behavioral variation promotes biased task performance and the emergence of a defensive caste in a social spider

The social spider Anelosimus studiosus exhibits a behavioral polymorphism where colony members express either a passive, tolerant behavioral tendency (social) or an aggressive, intolerant behavioral tendency (asocial). Here we test whether asocial individuals act as colony defenders by deflecting the suite of foreign (i.e., heterospecific) spider species that commonly exploit multi-female colonies. We (1) determined whether the phenotypic composition of colonies is associated with foreign spider abundance, (2) tested whether heterospecific spider abundance and diversity affect colony survival in the field, and (3) performed staged encounters between groups of A. studiosus and their colony-level predator Agelenopsis emertoni (A. emertoni)to determine whether asocial females exhibit more defensive behavior. We found that larger colonies harbor more foreign spiders, and the number of asocial colony members was negatively associated with foreign spider abundance. Additionally, colony persistence was negatively associated with the abundance and diversity of foreign spiders within colonies. In encounters with a colony-level predator, asocial females were more likely to exhibit escalatory behavior, and this might explain the negative association between the frequency of asocial females and the presence of foreign spider associates. Together, our results indicate that foreign spiders are detrimental to colony survival, and that asocial females play a defensive role in multi-female colonies.     

Condition dependence of male display coloration in a jumping spider (Habronattus pyrrithrix)

In many animals, conspicuous coloration functions as a quality signal. Indicator models predict that such colors should be variable and condition dependent. In Habronattus pyrrithrix jumping spiders, females are inconspicuously colored, while males display brilliant red faces, green legs, and white pedipalps during courtship. We tested the predictions of the indicator model in a field study and found that male body condition was positively correlated with the size, hue, and red chroma of a male’s facial patch and negatively correlated with the brightness of his green legs. These traits were more condition dependent than non-display colors. We then tested a dietary mechanism for condition dependence using two experiments. To understand how juvenile diet affects the development of coloration, we reared juvenile spiders on high- and low-quality diets and measured coloration at maturity. To understand how adult diet affects the maintenance of coloration, we fed wild-caught adults with high- or low-quality diets and compared their coloration after 45 days. In the first experiment, males fed high-quality diet had redder faces, suggesting that condition dependence is mediated by juvenile diet. In the second experiment, red coloration did not differ between treatments, suggesting that adult diet is not important for maintaining the color after it is produced at maturity. Diet had no effect on green coloration in either experiment. Our results show different degrees of condition dependence for male display colors. Because red is dependent on juvenile diet, it may signal health or foraging ability. We discuss evidence that green coloration is age dependent and alternatives to indicator models for colorful displays in jumping spiders.     

Stabilimenta characteristics of the spider Argiope argentata on small islands: support of the predator-defense hypothesis

Summary A variety of orb-weaving spider species construct stabilimenta, patterned areas of dense silk, typically near the hub of the orb. The adaptive significance of this construction, along with associated behaviors such as shuttling and vibrating, is much debated. Arigiope argentata on small islands of the Bahamas frequently possess stabilimenta; we studied 397 individuals of this species to investigate possible functions of their stabilimenta, paying particular attention to predator-defense hypotheses. Cruciform stabilimenta were commoner in all size classes of spiders than discoid stabilimenta or no stabilimentum at all; discoid stabilimenta occurred mostly among intermediate size classes. Within the cruciform type, two-segmented stabilimenta were especially common among the very smallest spiders. Size of cruciform stabilimenta showed a curvilinear relation to spider body length; the fitted curve for total segment length had a maximum at an intermediate spider length. We argue that this relationship (among other phenomena) supports an apparently-larger-size hypothesis, whereby intermediate-sized spiders in particular appear much larger than they actually are. This could discourage predators, including those that are gape-limited such as lizards. We argue that stabilimenta in the smallest spiders, in which typically two segments are opposed, so that they more or less line up, serve as camouflage. When disturbed experimentally, spiders with discoid stabilimenta shuttle to the opposite side of the centrally located stabilimentum. This seems an obvious defensive behavior and occurs less frequently among spiders with cruciform stabilimenta. Large spiders vibrate more frequently than small ones, but no relation exists between vibration frequency and stabilimentum type. We argue (see also Tolbert 1975) that vibrating behavior, in which the spider can become a blur, renders its location more difficult to discern and the spider more difficult to grasp, rather than increasing apparent size. Correspondence to: T.W. Schoener     

The impact of grazing on spider communities in a mesophytic calcareous dune grassland

During 1994–1995 and 1997–1998 spiders were sampled with pitfall traps in a botanically rich, mesophytic, calcareous dune grassland in Belgium. As a consequence of intensive cattle grazing, vegetation variation in a large part of the area had diminished. The study area was also patchily grazed by rabbits. Community analysis with TWINSPAN revealed five distinct spider communities. Ecological differentiation was best explained by combination of the habitat variables: distance from grazed or non-grazed vegetation,Rosa pimpinellifolia cover and grass cover in both summer and winter. Species diversity was highest in the border zone between the cattle-grazed and non cattle-grazed sites. Correlation of the most abundant spider species with the vegetation determinants explains the ecological differentiation between the spider communities. Species were classified into seven major groups that reflect the species’ habitat preferences. The group showing clear association with non cattle-grazed, tall vegetation consists of common species. Characteristic species for the intensively cattle-grazed sites are common aeronauts and rare species such asWalckenaeria stylifrons, Mastigusa arietina, Ceratinopsis romana andPardosa monticola. The latter are shown to be dependent on ungrazed vegetation for juvenile development and overwintering. Intensive grazing results in homogeneous short vegetation, which can only be colonized by ‘open ground’ species with a well-developed dispersal capacity, or by species which are not dependent on litter-rich situations for juvenile development. An extensive cattle grazing regime results in a patchy mosaic grassland where, in addition to the above mentioned groups of species, other species survive by migrating between the buffered litter rich ungrazed vegetation and the short vegetation. Additionally, some typical and rare species prefer the transition zone between the grazed and the ungrazed vegetation because they are associated with specific habitat structures or inhabiting ant-species. Nomenclature: Roberts (1987, 1995) forAraneae; van der Meijden et al. (1990) for vascular plants; Corly et al. (1981) for bryophytes; Schaminée et al. (1996) for vegetation associations.