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Bird-eating spiders
Introduces the large bird-eating spider, which is also referred to as a tarantula or theraphosa blondi.
Book
New species and new records of Phrynarachne crab spiders (Araneae, Thomisidae) from Southeast Asia
Two new species of Phrynarachne , P. gorochovi sp. nov. (♀), from Philippines (Luzon) and P. storozhenkoi sp. nov. (♀) from Malaysia (Borneo) are diagnosed, illustrated and described. Two species, P. ceylonica (O. Pickard-Cambridge, 1884) and P. decipiens Forbes, 1884 are reported from Laos for the first time and their females are redescribed in detail. The distribution of P. decipiens is discussed.
Journal Article
Painted Bunting (Passerina ciris) caught in the web of a giant lichen orb-weaver spider (Araneus bicentenarius)
Orb-weaver spiders weave large webs that are capable of entrapping various species of birds. We report a case of a male Painted Bunting (Passerina ciris) caught in the web of a giant lichen orb-weaver (Araneus bicentenarius). Most cases of bird entrapment in spider webs involve spiders with larger webs (often Nephila sp.) and very small birds, usually hummingbirds. Our case is noteworthy because we report a relatively large bird caught in a relatively small web. Furthermore, the geographic distribution of A. bicentenarius extends beyond the tropics and subtropics, which is where most reported cases of bird entrapment occur. This observation suggests that even small orb-weaver webs may pose a threat to relatively large birds, and that this risk may extend well beyond the regions most commonly associated with entrapment.
Journal Article
Movement of Aquatic Mercury Through Terrestrial Food Webs
Mercury has contaminated rivers worldwide, with health consequences for aquatic organisms and humans who consume them. Researchers have focused on aquatic birds as sentinels for mercury. However, trophic transfer between adjacent ecosystems could lead to the export of aquatic mercury to terrestrial habitats. Along a mercury-contaminated river in Virginia, United States, terrestrial birds had significantly elevated levels of mercury in their blood, similar to their aquatic-feeding counterparts. Diet analysis revealed that spiders delivered much of the dietary mercury. We conclude that aquatic mercury pollution can move into terrestrial habitats, where it biomagnifies to levels in songbirds that may cause adverse effects. Rivers contaminated with mercury may pose a threat to the many bird species that feed on predatory invertebrates in adjacent riparian habitats.
Journal Article
Protected areas facilitate species’ range expansions
The benefits of protected areas (PAs) for biodiversity have been questioned in the context of climate change because PAs are static, whereas the distributions of species are dynamic. Current PAs may, however, continue to be important if they provide suitable locations for species to colonize at their leading-edge range boundaries, thereby enabling spread into new regions. Here, we present an empirical assessment of the role of PAs as targets for colonization during recent range expansions. Records from intensive surveys revealed that seven bird and butterfly species have colonized PAs 4.2 (median) times more frequently than expected from the availability of PAs in the landscapes colonized. Records of an additional 256 invertebrate species with less-intensive surveys supported these findings and showed that 98% of species are disproportionately associated with PAs in newly colonized parts of their ranges. Although colonizing species favor PAs in general, species vary greatly in their reliance on PAs, reflecting differences in the dependence of individual species on particular habitats and other conditions that are available only in PAs. These findings highlight the importance of current PAs for facilitating range expansions and show that a small subset of the landscape receives a high proportion of colonizations by range-expanding species.
Journal Article
Increasing crop heterogeneity enhances multitrophic diversity across agricultural regions
Agricultural landscape homogenization has detrimental effects on biodiversity and key ecosystem services. Increasing agricultural landscape heterogeneity by increasing seminatural cover can help to mitigate biodiversity loss. However, the amount of seminatural cover is generally low and difficult to increase in many intensively managed agricultural landscapes. We hypothesized that increasing the heterogeneity of the crop mosaic itself (hereafter “crop heterogeneity”) can also have positive effects on biodiversity. In 8 contrasting regions of Europe and North America, we selected 435 landscapes along independent gradients of crop diversity and mean field size. Within each landscape, we selected 3 sampling sites in 1, 2, or 3 crop types. We sampled 7 taxa (plants, bees, butterflies, hoverflies, carabids, spiders, and birds) and calculated a synthetic index of multitrophic diversity at the landscape level. Increasing crop heterogeneity was more beneficial for multitrophic diversity than increasing seminatural cover. For instance, the effect of decreasing mean field size from 5 to 2.8 ha was as strong as the effect of increasing seminatural cover from 0.5 to 11%. Decreasing mean field size benefited multitrophic diversity even in the absence of seminatural vegetation between fields. Increasing the number of crop types sampled had a positive effect on landscape-level multitrophic diversity. However, the effect of increasing crop diversity in the landscape surrounding fields sampled depended on the amount of seminatural cover. Our study provides large-scale, multitrophic, cross-regional evidence that increasing crop heterogeneity can be an effective way to increase biodiversity in agricultural landscapes without taking land out of agricultural production.
Journal Article
‘Natural experiment’ Demonstrates Top-Down Control of Spiders by Birds on a Landscape Level
The combination of small-scale manipulative experiments and large-scale natural experiments provides a powerful approach for demonstrating the importance of top-down trophic control on the ecosystem scale. The most compelling natural experiments have come from studies examining the landscape-scale loss of apex predators like sea otters, wolves, fish and land crabs. Birds are dominant apex predators in terrestrial systems around the world, yet all studies on their role as predators have come from small-scale experiments; the top-down impact of bird loss on their arthropod prey has yet to be examined at a landscape scale. Here, we use a unique natural experiment, the extirpation of insectivorous birds from nearly all forests on the island of Guam by the invasive brown tree snake, to produce the first assessment of the impacts of bird loss on their prey. We focused on spiders because experimental studies showed a consistent top-down effect of birds on spiders. We conducted spider web surveys in native forest on Guam and three nearby islands with healthy bird populations. Spider web densities on the island of Guam were 40 times greater than densities on islands with birds during the wet season, and 2.3 times greater during the dry season. These results confirm the general trend from manipulative experiments conducted in other systems however, the effect size was much greater in this natural experiment than in most manipulative experiments. In addition, bird loss appears to have removed the seasonality of spider webs and led to larger webs in at least one spider species in the forests of Guam than on nearby islands with birds. We discuss several possible mechanisms for the observed changes. Overall, our results suggest that effect sizes from smaller-scale experimental studies may significantly underestimate the impact of bird loss on spider density as demonstrated by this large-scale natural experiment.
Journal Article
Trophic effects of vertebrate insectivores and carnivorous arthropods in a subtropical forest: the roles of functional redundancy and intraguild predation
Insectivorous predators play a crucial role in suppressing herbivore populations and mitigating herbivory in terrestrial ecosystems. However, the outcomes of ‘insectivore—herbivore—plant’ interactions are context dependent. This study examines the effects of vertebrate insectivores (birds and bats) and carnivorous arthropods (spiders) on herbivorous insects (caterpillars and sap suckers) and their host plant,
Machilus thunbergii
(Lauraceae), in a subtropical evergreen forest. We employed a factorial field experiment with four treatments: control (no exclusion), bird/bat exclusion, spider removal, and bird/bat exclusion plus spider removal. Forty trees (10 per treatment) were surveyed for herbivore abundance, degree of herbivory, and herbivore community composition. The results indicate that the predator treatments had no effects on sap suckers or sap-sucking damage. However, compared to the control, the leaf-chewing damage was higher in the bird/bat exclusion plus spider removal treatment, accompanied by shifts in leaf-chewer community composition and a trend toward increased leaf-chewer abundance. Spider abundance was lower in the control than in the bird/bat exclusion treatment, suggesting intraguild predation of spiders by birds and bats. Nevertheless, the leaf-chewing damage remained similar between these treatments, indicating that intraguild predation did not weaken the trophic cascade. This study is one of the few experiments that manipulate both vertebrate insectivores and carnivorous arthropods, and provides rare evidence that these two predator groups can perform complementary roles in suppressing herbivory. Our findings suggest that the strength of trophic interactions in the ‘insectivore—leaf chewer—plant’ system of this subtropical evergreen forest are likely to be relatively stable.
Journal Article
The impact of land use on non-native species incidence and number in local assemblages worldwide
While the regional distribution of non-native species is increasingly well documented for some taxa, global analyses of non-native species in local assemblages are still missing. Here, we use a worldwide collection of assemblages from five taxa - ants, birds, mammals, spiders and vascular plants - to assess whether the incidence, frequency and proportions of naturalised non-native species depend on type and intensity of land use. In plants, assemblages of primary vegetation are least invaded. In the other taxa, primary vegetation is among the least invaded land-use types, but one or several other types have equally low levels of occurrence, frequency and proportions of non-native species. High land use intensity is associated with higher non-native incidence and frequency in primary vegetation, while intensity effects are inconsistent for other land-use types. These findings highlight the potential dual role of unused primary vegetation in preserving native biodiversity and in conferring resistance against biological invasions.
Anthropogenic habitat modification is considered a driver of non-native species establishment. Here, the authors quantify the occurrence of non-native species in local assemblages of vascular plants, ants, spiders, birds and mammals, finding generally greater presence and frequency under disturbed land-use types.
Journal Article