Spatial-pattern analysis in a territorial spider: evidence for multi-scale effects

Territorial animals maintain a certain distance to neighbouring conspecifics, presumably leading to a regular spatial pattern through social spacing. Nevertheless, most animal populations are assumed to show aggregation at certain distance ranges, reflecting the scale dependency of spatial patterns. Leucorchestris arenicola (Araneae: Sparassidae) is a burrow-living spider species that shows territorial behaviour against conspecifics. A multi-scale approach in spatial analysis revealed that territory owners had fewer neighbours than expected under spatial randomness at distances up to 6 m. Behavioural field experiments showed that territory owners were able to perceive and react to burrow constructing neighbours up to at least 4 m distance from their own burrow. At larger distances individuals were often more aggregated than expected under spatial randomness. Analysing adult and immature relationships showed attraction between different development stages at small distances and avoidance at larger distances. The analysis reveals diverse spatial patterns in a territorial and cannibalistic species, showing that both behaviour and environment affect pattern development at different distances. The study outlines the importance of multi-scale approaches for spatial analysis and the need for accompanying experiments to facilitate the interpretation of results.     

Burrow-blocking behaviour in Geolycosa wrightii (Araneae: Lycosidae)

Patterns of behaviour associated with preventing wind-blown sand from entering the burrows of the wolf spider Geolycosa wrightii were investigated in a laboratory study. The method of closing the burrow depended upon the rate of sand entry. The spider employed a web block at low rates and used its body to block at high rates.     

Games spiders play. III: Cues underlying context-associated changes in agonistic behaviour

In this paper I consider the proximate cues underlying context-associated variation in the agonistic behaviour of the spider Agelenopsis aperta (Gertsch). At the initiation of a contest, individual opponents are shown to assess their relative weights; the subsequent behaviour of each is adjusted according to the result of the assessment. Escalation to potentially injurious behaviour early in the contest, for instance, is a threshold effect of weight bias. Several lines of evidence indicate, that only the territory Owner (resident) has information about the quality of a site at the initiation of a territorial dispute. (1) Owners of poor-quality sites that received food supplements exhibited significantly greater persistence and estimated energy expenditure in contests over these sites than unsupplemented individuals did over theirs. (2) A significant correlation was observed between web area and the behaviour of Owners, but not between web area and the behaviour of Intruders (individuals that encroach on occupied webs). (3) No correspondence was observed between spider body temperature and agonistic behaviour. (4) The presence or absence of prey on the web during the dispute did not affect the agonistic behaviour of either opponent. I conclude that the Intruder's behaviour is in some way adjusted to that of the Owner rather than directly to some aspect of the disputed site. Partial correlation analysis show site quality to have a greater influence on agonistic behaviour than weight bias, although both are important determinants of spider behaviour in territorial disputes.     

Local population success in heterogeneous habitats: reciprocal transplant experiments completed on a desert spider

Reciprocal transplant experiments were completed to test for selection against the mixing of behavioural phenotypes in a desert spider. Most Agelenopsis aperta populations experience low prey abundances and competition for web‐sites that provide shelter from thermal extremes. These conditions favour aggressiveness towards both prey and conspecifics (an ‘arid‐land behavioural phenotype’). The spider also occupies narrow stretches of riparian habitat bordering spring‐fed streams and rivers. Here it is released from competition for prey and foraging sites, but is subject to predation by birds. A less aggressive/more fearful behaviour is selected for in these riparian habitats (a ‘riparian behavioural phenotype’). Previous work with this spider indicates that there is genetic differentiation between arid‐land and riparian populations. However, the degree to which genetic differentiation is achieved may be limited by gene flow. Reciprocal sets of enclosures were established in: (1) a dry evergreen woodland site (arid‐land phenotype) and (2) a neighbouring riparian site (riparian phenotype) in south‐eastern Arizona. Equal numbers of field collected, early instar A. aperta were introduced into native and transplant enclosures in each habitat. After 6 months of site‐imposed selection, survivorship was determined and growth estimates and behavioural trials completed on spiders remaining in the different enclosures. The same behavioural test was subsequently applied to lab‐reared offspring of the spiders surviving the respective selection regimes. Riparian transplants showed both poor survival and retarded growth in the dry woodland habitat when compared with both arid‐land and riparian natives. Arid‐land transplants that survived, however, grew equally well in riparian habitat as did dry woodland and riparian natives. Behavioural assays conducted on test subjects after selection and on their offspring reared in a controlled laboratory environment indicate that phenotypes that were inappropriate to the respective habitats were selected against in the transplant experiments. The frequency distribution of transplant spider behaviour on a continuum from fearful to aggressive was intermediate between that exhibited by respective native riparian and dry woodland spiders. It is concluded that while arid‐land and riparian behavioural ecotypes do exist, directional gene flow of arid‐land phenotypes into riparian habitat limits population subdivision.     

Two Trichosporon species isolated from Central-European mygalomorph spiders (Araneae: Mygalomorphae)

Trichosporon (Dikarya: Basidiomycota) is a genus of anamorphic yeasts typically associated with soil and water, although many species are causative agents of diseases in animals and man. Here we provide the first compelling evidence that spiders can be occasionally colonized by at least two Trichosporon species. Trichosporon dulcitum (Berkhout) Weijman 1979 was isolated from the exoskeleton of purse-web spider Atypus piceus, while Trichosporon porosum (Stautz) Middelhoven, Scorzetti & Fell 2001 was isolated from the exoskeleton of purse-web spider Atypus affinis. Both of the species were identified based on DNA sequence analysis of the host specimens displaying macroscopic signs of the superficial white mycosis on their exoskeleton. Only two specimens with macroscopic signs of superficial yeast growth were identified among the 125 individuals of A. affinis, A. piceus and Atypus muralis examined that were collected at various sites throughout the Czech Republic. The consistent burrow microclimate, uninterrupted occupancy of the single burrow for several subsequent years, and presence of prey remnants in the burrow below the purse-web may play a role in the course of infection of the mygalomorphs examined. The phylogenetic relationships of Trichosporon species are analyzed, concluding that association with invertebrates clusters predominantly among four groups of closely related species in independent Trichosporon clades.     

Complex-to-Predict Generational Shift between Nested and Clustered Organization of Individual Prey Networks in Digger Wasps

Although diet has traditionally been considered to be a property of the species or populations as a whole, there is nowadays extensive knowledge that individual specialization is widespread among animal populations. Nevertheless, the factors determining the shape of interactions within food webs remain largely undiscovered, especially in predatory insects. We used an aggregation of the digger wasp Bembix merceti to 1) analyse patterns of individual prey use across three flying seasons in a network–based context; and 2) test the effect of four potential factors that might explain network topologies (wasp mass, nest spatial distribution, simultaneous nest-provisioning, prey availability). Inter-individual diet variation was found in all three years, under different predator-prey network topologies: Individuals arranged in dietary clusters and displayed a checkerboard pattern in 2009, but showed nestedness in 2008 and 2010. Network topologies were not fully explained by the tested factors. Larger females consumed a higher proportion of the total number of prey species captured by the population as a whole, in such a way that nested patterns may arise from mass-dependent prey spectrum width. Conversely, individuals with similar body mass didn’t form clusters. Nested patterns seemed to be associated with a greater availability of the main prey species (a proxy for reduced intra-specific competition). Thus, according with theory, clusters seemed to appear when competition increased. On the other hand, the nests of the individuals belonging to a given cluster were not more closely located, and neither did individuals within a cluster provision their nests simultaneously. Thus, a female-female copying behaviour during foraging was unlikely. In conclusion, wasp populations can maintain a considerable individual variation across years under different food web organizations. The tested factors only partially accounted for the shift in network properties, and new analyses should be carried out to elucidate how diet network topologies arise in wasp populations.     

Phenotypic variability along a climatic gradient in a perennial afrotropical rainforest understorey herb

Plants evolved in response to climatic conditions, which shaped their geographic distribution, functional traits and genetic composition. In the face of climatic changes, plants have to react by either genetic adaptation, phenotypic plasticity or geographic range shift. Their reaction potential depends on their phenotypic and genetic variability which can be evaluated through regional scale trait estimates, however, little is known here about tropical African plants. To start filling this gap of knowledge, the aim of this study was to estimate the phenotypic variability in a widespread perennial herb from the understorey of tropical African rainforests: Sarcophrynium prionogonium (Marantaceae). We surveyed 211 individuals from eight populations distributed across four sites in Cameroon covering largely the climatic range of the study species. Fourteen key functional traits were measured monthly for 18 months (2013–2014). Individuals of the study species persisted under a wide range of environmental conditions and there was considerable intraspecific variability within and across populations. Still, plant vegetative growth decreased with dryness. Productivity was positively related to a combination of high temperatures and precipitation and under these favourable conditions strongly shaped by light. Seasonal patterns of flower and fruit development were strongly associated with seasonal rainfall. Thus, the predicted increased dryness in tropical Africa might be disadvantageous for the study species. In the past, plants reacted to such aridification tendencies (e.g. during the Pleistocene glacial cycles) by retracting to moist refugia. The current climatic changes, however, being much faster and larger might provide new challenges.     

Costs and benefits of facultative aggregating behaviour in the orb-spinning spider Gasteracantha minax Thorell (Araneae: Araneidae)

Abstract The potential costs and benefits of foraging in aggregations are examined for the orb-spinning spider Gasteracantha minax. Web-site tenacity is low in this species; individuals frequently move among sites, thereby joining aggregations of different sizes. Female spiders in aggregations suffered lower predation rates and attracted more males than their solitary counterparts. However, aggregated eggsacs, probably produced by females in aggregations, experienced higher rates of parasitism than solitary eggsacs. We found no evidence of higher prey capture success rates among spiders in aggregations. However, we demonstrate a novel way in which spiders can increase their foraging efficiency by decreasing silk investment. A spider spinning a web within an existing aggregation can attach the support threads of its web to those of other webs, thereby exploiting the silk produced by other spiders.     

Thermal biology,population fluctuations and implications of temperature extremes for the management of two globally significant insect pests

The link between environmental temperature, physiological processes and population fluctuations is a significant aspect of insect pest management. Here, we explore how thermal biology affects the population abundance of two globally significant pest fruit fly species, Ceratitis capitata (medfly) and C. rosa (Natal fruit fly), including irradiated individuals and those expressing a temperature sensitive lethal (tsl) mutation that are used in the sterile insect technique. Results show that upper and lower lethal temperatures are seldom encountered at the field sites, while critical minimum temperatures for activity and lower developmental thresholds are crossed more frequently. Estimates of abundance revealed that C. capitata are active year-round, but abundance declines markedly during winter. Temporal autocorrelation of average fortnightly trap captures and of development time, estimated from an integrated model to calculate available degree days, show similar seasonal lags suggesting that population increases in early spring occur after sufficient degree-days have accumulated. By contrast, population collapses coincide tightly with increasing frequency of low temperature events that fall below critical minimum temperatures for activity. Individuals of C. capitata expressing the tsl mutation show greater critical thermal maxima and greater longevity under field conditions than reference individuals. Taken together, this evidence suggests that low temperatures limit populations in the Western Cape, South Africa and likely do so elsewhere. Increasing temperature extremes and warming climates generally may extend the season over which these species are active, and could increase abundance. The sterile insect technique may prove profitable as climates change given that laboratory-reared tsl flies have an advantage under warmer conditions.     

Burrow decorations as antipredatory devices

Animal decorations are normally interpreted as signals of quality.In spiders, however, decorations may have different functions,including the attraction of prey to the web or making the spidercryptic to predators. To date, there is scant evidence for thelatter hypothesis. Here we use the burrow-decorating wolf spiderLycosa tarantula to test whether turrets around the burrow serveto prevent burrow invasion and predation from the Occitan scorpionButhus occitanus. We located spiders and scorpions in fieldenclosures and manipulated the presence or absence of decorationsor turrets. We found that the presence of the turret decreasesthe rate of burrow invasion and improves spider survival, possiblybecause the turret makes the burrow cryptic to scorpions. Inaddition, a field survey showed that burrows with larger decorationshad a lower chance of being invaded by scorpions. These resultsprovide evidence that the decoration has an antipredatory functionin nature.     

The role of prey availability in aggregative behaviour of the orb weaving spider Tetragnatha elongata

Like many spider species, Tetragnatha elongata exhibits considerable flexibility in its spacing pattern as a response to variable levels of prey abundance. This study examines the extent and form of spider aggregation at high prey density. In experiments in which their respective densities were manipulated, when spider density was high, excess prey allowed individuals (1) a significant reduction in web building, and (2) indiscriminate use of pre-laid silk. These effects were not observed at low spider density. These results are discussed in the context of ‘risk-sensitive’ foraging theory, which shows how this type of behaviour in an aggregation might be adopted as a means for reducing resource variance. Such an approach indicates a possible means through which sociality might be initiated.     

Calibration of a burrow count index for the Indian desert jird, Meriones hurrianae

Population estimates, often difficult to acquire, warrantee the use of an index as an economical substitute for rapid assessments of populations. We estimated population size of the little known social, semi-fossorial Indian desert jird (Meriones hurrianae) in Kachchh, Gujarat, India under closed population capture-mark-recapture (CMR) framework to calibrate a burrow count index for the species. A total of 147 individuals were trapped in 16 colonies using baited Sherman traps and the number of burrow entrances at each colony was recorded. Data from colonies with low number of captures were pooled to estimate capture probability using Huggins heterogeneity models with gender, site, body weight and age category as covariates in Program MARK. Colony sizes ranged from 2 to 46 individuals. The number of burrow entrances was calibrated against CMR-based population estimates using least squares regression (n = 16, adjusted R ² = 0.96, t = 18.18, P < 0.001). The index was further validated using Jackknife (JK) analysis where JK-predicted population estimates strongly correlated with CMR estimates (r = 0.96, P < 0.001). In habitats and climatic conditions similar to Kachchh and within the range of colony sizes sampled, our calibrated index can be a valuable and effective tool for large scale surveys of the desert jird, which occupies a keystone trophic level in the semi-arid ecosystem.     

Breeding latitude leads to different temporal but not spatial organization of the annual cycle in a long‐distance migrant

The temporal and spatial organization of the annual cycle according to local conditions is of crucial importance for individuals’ fitness. Moreover, which sites and when particular sites are used can have profound consequences especially for migratory animals, because the two factors shape interactions within and between populations, as well as between animal and the environment. Here, we compare spatial and temporal patterns of two latitudinally separated breeding populations of a trans‐Equatorial passerine migrant, the collared flycatcher Ficedula albicollis, throughout the annual cycle. We found that migration routes and non‐breeding residency areas of the two populations largely overlapped. Due to climatic constraints, however, the onset of breeding in the northern population was approximately two weeks later than that of the southern population. We demonstrate that this temporal offset between the populations carries‐over from breeding to the entire annual cycle. The northern population was consistently later in timing of all subsequent annual events – autumn migration, non‐breeding residence period, spring migration and the following breeding. Such year‐round spatiotemporal patterns suggest that annual schedules are endogenously controlled with breeding latitude as the decisive element pre‐determining the timing of annual events in our study populations.     

The global relationship between climate,net primary production and the diet of spiders

Aim We compiled data on prey utilization of spiders at a global scale to better understand the relationship between current climate or net primary production (NPP) and diet breadth, evenness and composition in spiders. We test whether the productivity and the diversity–climatic‐stability (DCS) hypotheses focusing on diversity patterns may also explain global patterns in prey utilization by web‐building and cursorial spiders. Location A global dataset of 95 data points from semi‐natural and natural terrestrial habitats spanning 41.3° S to 56.1° N. Methods We collected data on spider prey (29 groups, mostly order‐level invertebrate taxa) through extensive literature research to identify the relationship between climatic conditions and NPP and spider diets based on 66 studies of prey composition in 82 spider species. Results The number of prey groups in spider diets was positively related to NPP, after accounting for differences in sampling effort in the original studies. In general, diet breadth was significantly higher for spider species in tropical environments. Prey individuals in spider diets were more evenly distributed among different prey groups in warmer environments with lower fluctuations in precipitation. Collembola and other spiders were more common prey for spiders with a cursorial hunting mode. Myriapoda and Collembola were more common prey in cooler climates with more stable precipitation, whereas Isoptera, Lepidoptera, Psocoptera and Coleoptera showed the opposite pattern. Main conclusions The positive relationship between diet breadth and NPP and the negative relationship between prey evenness and seasonality in precipitation support the productivity and the DCS hypotheses, respectively. This effect on global patterns of invertebrate predator–prey interactions suggests that trophic interactions between spiders and their prey are sensitive to climatic conditions. Climatic conditions may not only affect spider community composition, but also considerably alter the functional role of these abundant invertebrate predators in terrestrial ecosystems.     

Development of an index of abundance for pygmy rabbit populations

The pygmy rabbit (Brachylagus idahoensis) is a cryptic, burrowing lagomorph of conservation concern for which an efficient method to monitor populations is needed for conservation planning. We developed an index of abundance based on density of active burrow systems at 7 sites (57.2–118.5 ha) in east central Idaho. We conducted censuses of burrow systems and used mark-resight surveys of 80 radio-collared individuals to estimate density of rabbits. At 5 sites, we also used a second method to estimate rabbit numbers based on presence of tracks in snow around burrow systems. We evaluated patterns of burrow use by individuals and examined the relationship between vegetation structure and density of rabbits. Density of active burrow systems varied from 0.19 to 3.46 per ha, and density of rabbits ranged from 0.02 to 0.46 per ha. Number of burrow systems used by individuals increased with density of available burrows, which supported a nonlinear relationship between abundance of burrows and rabbits. Population density increased curvilinearly with density of active burrows accounting for >75% of the variation (r² = 0.79) in population estimates across sites. We documented a positive relationship between visual obstruction of vegetation and density of rabbits across 6 of the study sites. Our results suggest that density of burrows can serve as an index for monitoring changes in abundance of pygmy rabbits in east central Idaho and that this index also might be useful for monitoring changes in relative abundance over time at other locations. To assess abundance at larger spatial scales or across different regions, the index should be calibrated under regional conditions and site-level covariates should be evaluated. © 2011 The Wildlife Society.     

A novel feeding behaviour in wild redfronted lemurs (Eulemur rufifrons): depletion of spider nests

Reports on behavioural innovations in wild primate populations as well as on their transmission are rare. Here, we report observations suggesting that redfronted lemurs (Eulemur rufifrons) invent new behaviours in the wild. We observed a novel feeding behaviour in redfronted lemurs in Kirindy Forest, western Madagascar. The feeding behaviour consisted of depletion of nests of a social spider species (Stegodyphus sp.). The behaviour was observed in only one out of four study groups, although spider nests were present in the home ranges of all four groups. The behaviour was exhibited in three different years (2009, 2011, 2012) and appears to be re-invented from time to time. Interestingly, in 2011 this behaviour was shown by four individuals and probably spread within the group. This feeding behaviour has only been observed between the middle of June and early August (i.e. the early dry season), and nests were found to be empty later on, suggesting that these nests are available as a food source only seasonally. Our observation contributes a rare case of behavioural innovations in a wild primate population.     

棉田蜘蛛混合种群空间格局分析及应用

1996年5月上旬至下旬,在山西运城地区临猗县,选择高水肥及中水肥棉田进行蜘蛛混合种群空间格局的调查分析。用经典频次法分析,大部分样本符合负二项分布,少数样本有多解和无解现象。9种聚集指标结果均符合聚集分布型,聚类分析结果表明,9种指标可按其性质分成3类。Iwao M~＃-m模型为M~＃=3.5151 1.4765 m,改进的M~＃-M模型为M~＃=2.6423 1.9587 m-0.0246 m~2,Taylor的幂法则式为S~2=22.089M~(2.6466),其结果均为聚集分布。应用以上分析结果,建立棉田蜘蛛混合种群调查的简化抽样方案。用零样出现的百分率来估计百株蜘蛛数量的指数回归式为:P_O=(0.6011/(0.6011 m)~(0.6011);用有蜘蛛的株率来估计百株蛛量,则用以下指数回归式:Y=256.52~(1.5345)。     

A virtual robot to model the use of regenerated legs in a web-building spider

The garden cross orb-spider, Araneus diadematus, shows behavioural responses to leg loss and regeneration that are reflected in the geometry of the web's capture spiral. We created a virtual spider robot that mimicked the web construction behaviour of thus handicapped real spiders. We used this approach to test the correctness and consistency of hypotheses about orb web construction. The behaviour of our virtual robot was implemented in a rule-based system supervising behaviour patterns that communicated with the robot's sensors and motors. By building the typical web of a nonhandicapped spider our first model failed and led to new observations on real spiders. We realized that in addition to leg position, leg posture could also be of importance. The implementation of this new hypothesis greatly improved the results of our simulation of a handicapped spider. Now simulated webs, like the real webs of handicapped spiders, had significantly more gaps in successive spiral turns compared with webs of nonhandicapped spiders. Moreover, webs built by the improved virtual spiders intercepted prey as well as the digitized real webs. However, the main factors that affected web interception frequency were prey size, size of capture area and individual variance; having a regenerated leg, surprisingly, was relatively unimportant for this trait. Copyright 1999 The Association for the Study of Animal Behaviour.     

Habitat selection in a large orb‐weaving spider: vegetational complexity determines site selection and distribution

1. The distribution of the large orb‐weaving spider Argiope trifasciata in old field habitats of North America and the habitat selection process this species used was studied for 2 years. 2. Because web spiders have limited dispersal abilities and an energetically costly prey capture device, they do not have the ability to sample potential foraging sites. Structural complexity of the vegetation to which the web must be attached is relatively easy to assess. The hypothesis that the structural complexity is a primary factor in determining initial web site selection was tested both by relating the natural distribution of the spiders across habitats to vegetational complexity and by manipulating the complexity of the habitats in a series of experiments. 3. Argiope trifasciata was not distributed evenly among three old field vegetation types. Habitat complexity was related to spider density in both years although no measure of insect activity, prey capture, or prey consumption was correlated with spider distribution. 4. Three experimental manipulations were conducted to test the impact of habitat structure on spider establishment: (1) the amount of natural vegetation was reduced, (2) structures were added to a simple habitat, and (3) the complexity of the structures added was varied. In each case, spiders were introduced and establishment of webs was monitored. In all manipulations, spider establishment was related to the complexity of the substrate available. 5. These results are important for understanding the cues that influence foraging site selection and therefore provide insight into the distribution of species with limited dispersal abilities and high site investment requirements.     

Nest site choice compensates for climate effects on sex ratios in a lizard with environmental sex determination

Theoretical models suggest that in changing environments natural selection on two traits, maternal nesting behaviour and pivotal temperatures (those that divide the sexes) is important for maintaining viable offspring sex ratios in species with environmental sex determination (ESD). Empirical evidence, however, is lacking. In this paper, we provide such evidence from a study of clinal variation in four sex-determining traits (maternal nesting behaviour, pivotal temperatures, nesting phenology, and nest depth) in Physignathus lesueurii, a wide-ranging ESD lizard inhabiting eastern Australia. Despite marked differences in air and soil temperatures across our five study sites spanning 19° latitude and 1200 m in elevation, nest temperatures did not differ significantly among sites. Lizards compensated for climatic differences chiefly by selecting more open nest sites with higher incident radiation at cooler sites. Clinal variation in the onset of nesting also compensated for climatic differences, but to a lesser extent. There was no evidence of compensation through pivotal temperatures or nest depth. More broadly, our results extend to the egg stage the life history prediction that behaviour is the chief compensatory mechanism for climatic differences experienced by species spanning environmental extremes. Furthermore, our study was unique in revealing that nest site choice influenced mainly the daily range in nest temperatures, rather than mean temperatures, in a shallow-nesting reptile. Finally, indirect evidence suggests that the cue used by nesting lizards was radiation or temperature (through basking or assessing substrate temperatures), not visual detection of canopy openness. We conclude that maternal nesting behaviour and nesting phenology are traits subject to sex ratio selection in P. lesueurii, and thus, must be considered among the repertoire of ESD species for responding to climate change.