Mixed-species groups in bats: non-random roost associations and roost selection in neotropical understory bats

Background Mixed-species groups in animals have been shown to confer antipredator, foraging and other benefits to their members that may provide selective advantages. In most cases, however, it is unclear whether functional benefits are a principal driver of heterospecific groups, or whether groups simply result from simultaneous exploitation of common resources. Mixed-species groups that form independently of environmental conditions may, however, evidence direct benefits of species associations. Bats are among the most gregarious mammals, with sometimes thousands of individuals of various species roosting communally. Despite numerous potential functional benefits of such mixed-species roosting groups, interspecific attraction has never been shown. To explore alternative explanations for mixed-species roosting, we studied roost selection in a speciose neotropical understory bat community in lowland rainforest in Costa Rica. Long term roost data were recorded over 10 years in a total of 133 roosts comprising both natural roosts and structurally uniform artificial roosts. We modelled bat roost occupancy and abundance in each roost type and in forest and pasture habitats to quantify the effects of roost- and environmental variability. Results We found that bat species presence in natural roosts is predictable from habitat and structural roost parameters, but that the presence and abundance of other bat species further modifies roost choice. One third of the 12 study species were found to actively associate with selected other bat species in roosts (e.g. Glossophaga commissarisi with Carollia sowelli). Other species did not engage in communal roosting, which in some cases indicates a role for negative interspecific interactions, such as roost competition. Conclusions Mixed-species roosting may provide thermoregulatory benefits, reduce intraspecific competition and promote interspecific information transfer, and hence some heterospecific associations may be selected for in bats. Overall, our study contributes to an improved understanding of the array of factors that shape diverse tropical bat communities and drive the dynamics of heterospecific grouping in mammals more generally.

Interspecific attraction between ground-nesting songbirds and ants: the role of nest-site selection

Background Interspecific interactions within ecological networks can influence animal fitness and behaviour, including nest-site selection of birds and ants. Previous studies revealed that nesting birds and ants may benefit from cohabitation, with interspecific attraction through their nest-site choice, but mutual interactions have not yet been tested. We explored a previously undescribed ecological link between ground-nesting birds and ants raising their own broods (larvae and pupae) within the birds’ nests in a temperate primeval forest of lowland Europe. We tested whether the occurrence of ant broods within bird nests resulted from a mutual or one-sided interspecific attraction that operated through nest-site choice and was modified by weather conditions. Results We found a non-random occupation of bird nests by ants raising their own broods within them, which indicated interspecific attraction driven solely by the ants. The birds’ preference to nest near tussocks of vegetation showed little overlap with the most frequent placement of ant colonies among fallen deciduous tree-leaves, dead wood and moss. Additionally, birds did not appear to select forest localities with high densities of ant colonies. The occurrence of ant broods within bird nests was also unrelated to bird nest placement near to specific habitat features. The attractiveness of bird nests to ants appeared to increase with the thermal activity of the birds warming their nests, and also during cool and wet weather when the occurrence of ant broods within bird nests was most frequent. Ants often remained in the nests after the birds had vacated them, with only a slight reduction in the probability of ant brood occurrence over time. Conclusions The natural patterns of bird nest colonisation by ants support the hypothesis of ants’ attraction to warm nests of birds to raise their broods under advantageous thermal conditions. Similar relationships may occur between other warm-blooded, nest-building vertebrates and nest-dwelling invertebrates, which depend on ambient temperatures. The findings advance our understanding of these poorly recognised interspecific interactions, and can inform future studies of ecological networks.

Intraspecific and interspecific attraction of threeTomicusbeetle species during the shoot-feeding phase

The shoot beetlesTomicus minor, Tomicus yunnanensis, andTomicus brevipilosushave been decimatingPinus yunnanensistrees for more than 30 years in Southwestern China. To understand the chemical ecological relationship between pines andTomicus, and among the three beetle species, we compared the attraction of these beetles to damaged shoots, extracts from damaged shoots, and volatiles from damaged shoots collected by the dynamic headspace sampling method. Experiments were performed using a modified open-arena olfactometer. The maleT. minorand both sexes ofT. brevipilosuswere more strongly attracted to damaged shoots than to undamaged shoots and they showed attraction to shoots damaged by the same species. FemaleT. minorand both sexes ofT. yunnanensiswere attracted to shoots damaged by femaleT. brevipilosus. The three beetle species were attracted to shoot extracts and dynamic headspace volatiles from shoots damaged by the same species and sex. FemaleT. minorand maleT. yunnanensiswere also attracted to dynamic headspace volatiles from shoots damaged by both sexes ofT. brevipilosus. The results suggested that specific semiochemicals that are induced or produced byT. brevipilosusalso attractT. minorandT. yunnanensis. The semiochemicals in damaged shoots affect the attraction of the three beetle species and play an important chemical communication role in weakening the host trees during the beetles’ shoot-feeding phase.

Olfactory response to beetle-produced volatiles and host-food attractants by Oryzaephilus surinamensis and O. mercator

A two-choice, pitfall olfactometer which utilizes a petri plate with suspended glass vials was employed to test the response of Oryzaephilus surinamensis (L.) and O. mercator (Fauvel) to various volatile stimuli. Male and female beetles of both species were attracted to pentane extracts of Porapak Q trapped volatiles from beetles, frass, rolled oats, and brewer's yeast over a wide range of stimulus concentrations. For both species, male and female frass contained attractive volatiles in addition to those from unused growth medium. This result and the attractiveness of volatiles from beetles suggest that both sexes produce an aggregation pheromone. Additionally, interspecific attraction to beetle and frass volatiles was demonstrated.

SEX PHEROMONE RESPONSES OF CHORISTONEURA SPP. AND THEIR HYBRIDS (LEPIDOPTERA: TORTRICIDAE)

Field studies in Ontario, Oregon, and California on interspecific attraction and inhibition among the coniferophagous species of Choristoneura (the spruce budworm and its allies) confirmed specific pheromonal differences among the species. Of the three species that are mutually attractive and whose males are attracted by blends of trans- and cis-11-tetradecenal, C. fumiferana, C. biennis, and C. occidentalis, catches of C. fumiferana males in traps baited with C. fumiferana females were significantly reduced by the presence of females from a second group in which it is believed the females produce trans-11-tetradecenyl acetate. Catches of C. occidentalis males by C. occidentalis females were not affected in this way. F1 hybrids and backcrosses between an aldehyde-producing species and an acetate-producing species produced females that were attractive to males of one or other of the parent species, although some females were not attractive to either. Individual females never attracted males of both parent species, and of those that were attractive, more were attractive to males of the aldehyde species than to males of the acetate species. The results suggest sex-controlled inheritance and expression.

FOREST LEPIDOPTERA ATTRACTED BY KNOWN SEX ATTRACTANTS OF WESTERN SPRUCE BUDWORMS, CHORISTONEURA SPP. (LEPIDOPTERA: TORTRICIDAE)

Field tests of (E)-11-tetradecenal and (E)-11-tetradecenyl acetate, the respective sex attractants for western spruce budworm, Choristoneura occidentalis Freeman and the Modoc budworm, C. viridis Freeman, revealed that these compounds attract several other forest Lepidoptera. The acetate attracted a total of 14 species representing seven families, and the aldehyde accounted for nine species representing four families. This interspecific attraction could influence budworm trapping efficiency and interpretation of results, because of the abundance of other responding species and the fact that two of the species resemble Choristoneura adults in appearance.