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Foraging ranges of insectivorous bats shift relative to changes in mosquito abundance.

ABSTRACT: The need to develop effective management strategies for insectivorous bat populations requires an understanding of factors influencing habitat use. Availability of pest prey, such as mosquitoes is likely to be one such factor. To assess whether this is the case, we radio-tracked Vespadelus vulturnus Thomas (little forest bat), a predator of Aedes vigilax Skuse (saltmarsh mosquito), in saltmarsh and adjacent coastal swamp forest during periods of high and low Ae. vigilax abundance. When mosquito abundance in structurally-open saltmarsh was similar to the more cluttered coastal swamp forest, use of saltmarsh by V. vulturnus was disproportionately greater than its availability, with saltmarsh selected preferentially for foraging. However, at times of low Ae. vigilax abundance in saltmarsh, use of saltmarsh by V. vulturnus was reduced and all habitats were used in proportion to availability in the study area. This is the first radio-tracking study to demonstrate a shift in foraging range by an insectivorous bat species correlated with fluctuations in the distribution and abundance of a particular prey resource. The shift in foraging range by V. vulturnus, corresponding with a spatio-temporal variation in abundance of Ae. vigilax highlights the importance of mosquitoes as a dietary item. Broadscale pest control of Ae. vigilax may have ecological implications for the diet and habitat use of V. vulturnus. An adaptive management approach is proposed, whereby careful monitoring of insectivorous bat populations is recommended before and after any application of broadscale mosquito control measures. We also suggest a precautionary approach is taken such that broadscale control of mosquitoes avoids the lactation period of bats, a time when their energetic demands are greatest and when there is reduced risk of contracting mosquito-borne diseases transmitted by Ae. vigilax.

SUBMITTER: Gonsalves L

PROVIDER: S-EPMC3646781 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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Foraging ranges of insectivorous bats shift relative to changes in mosquito abundance.

Gonsalves Leroy L Law Brad B Webb Cameron C Monamy Vaughan V

PloS one 20130507 5

The need to develop effective management strategies for insectivorous bat populations requires an understanding of factors influencing habitat use. Availability of pest prey, such as mosquitoes is likely to be one such factor. To assess whether this is the case, we radio-tracked Vespadelus vulturnus Thomas (little forest bat), a predator of Aedes vigilax Skuse (saltmarsh mosquito), in saltmarsh and adjacent coastal swamp forest during periods of high and low Ae. vigilax abundance. When mosquito ...[more]

PMID: 23667699

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Project description:Insectivorous bats have often been touted as biological control for mosquito populations. However, mosquitoes generally represent only a small proportion of bat diet. Given the small size of mosquitoes, restrictions imposed on prey detectability by low frequency echolocation, and variable field metabolic rates (FMR), mosquitoes may not be available to or profitable for all bats. This study investigated whether consumption of mosquitoes was influenced by bat size, which is negatively correlated with echolocation frequency but positively correlated with bat FMR. To assess this, we investigated diets of five eastern Australian bat species (Vespadelus vulturnus Thomas, V. pumilus Gray, Miniopterus australis Tomes, Nyctophilus gouldi Tomes and Chalinolobus gouldii Gray) ranging in size from 4-14 g in coastal forest, using molecular analysis of fecal DNA. Abundances of potential mosquito and non-mosquito prey were concurrently measured to provide data on relative prey abundance. Aedes vigilax was locally the most abundant mosquito species, while Lepidoptera the most abundant insect order. A diverse range of prey was detected in bat feces, although members of Lepidoptera dominated, reflecting relative abundance at trap sites. Consumption of mosquitoes was restricted to V. vulturnus and V. pumilus, two smaller sized bats (4 and 4.5 g). Although mosquitoes were not commonly detected in feces of V. pumilus, they were present in feces of 55 % of V. vulturnus individuals. To meet nightly FMR requirements, Vespadelus spp. would need to consume ~600-660 mosquitoes on a mosquito-only diet, or ~160-180 similar sized moths on a moth-only diet. Lower relative profitability of mosquitoes may provide an explanation for the low level of mosquito consumption among these bats and the absence of mosquitoes in feces of larger bats. Smaller sized bats, especially V. vulturnus, are likely to be those most sensitive to reductions in mosquito abundance and should be monitored during mosquito control activities.

Project description:The increased use of pesticides and tillage intensification is known to negatively affect biodiversity. Changes in these agricultural practices such as herbicide and tillage reduction have variable effects among taxa, especially at the top of the trophic network including insectivorous bats. Very few studies compared the effects of agricultural practices on such taxa, and overall, only as a comparison of conventional versus organic farming without accurately accounting for underlying practices, especially in conventional where many alternatives exist. Divergent results founded in these previous studies could be driven by this lack of clarification about some unconsidered practices inside both conventional and organic systems. We simultaneously compared, over whole nights, bat activity on contiguous wheat fields of one organic and three conventional farming systems located in an intensive agricultural landscape. The studied organic fields (OT) used tillage (i.e., inversion of soil) without chemical inputs. In studied conventional fields, differences consisted of the following: tillage using few herbicides (T), conservation tillage (i.e., no inversion of soil) using few herbicides (CT), and conservation tillage using more herbicide (CTH), to control weeds. Using 64 recording sites (OT = 12; T = 21; CT = 13; CTH = 18), we sampled several sites per system placed inside the fields each night. We showed that bat activity was always higher in OT than in T systems for two (Pipistrellus kuhlii and Pipistrellus pipistrellus) of three species and for one (Pipistrellus spp.) of two genera, as well as greater species richness. The same results were found for the CT versus T system comparison. CTH system showed higher activity than T for only one genus (Pipistrellus spp.). We did not detect any differences between OT and CT systems, and CT showed higher activity than CTH system for only one species (Pipistrellus kuhlii). Activity in OT of Pipistrellus spp. was overall 3.6 and 9.3 times higher than CTH and T systems, respectively, and 6.9 times higher in CT than T systems. Our results highlight an important benefit of organic farming and contrasted effects in conventional farming. That there were no differences detected between the organic and one conventional system is a major result. This demonstrates that even if organic farming is presently difficult to implement and requires a change of economic context for farmers, considerable and easy improvements in conventional farming are attainable, while maintaining yields and approaching the ecological benefits of organic methods.

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Foraging ranges of insectivorous bats shift relative to changes in mosquito abundance.

Publications

Foraging ranges of insectivorous bats shift relative to changes in mosquito abundance.

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