Vaughan Monamy

Competition between Two Australian Rodent Species: A Regression Analysis

Empirical evidence and observations suggest that competition exists between two native rodents, Rattus lutreolus velutinus and Pseudomys higginsi , living in a wet sclerophyll forest, Tasmania, Australia. We used a standardized regression technique to assess competition between the two species and its temporal changes throughout the year. With our time-series data, we also tested the validity of our estimated competition coefficients by comparing regression residuals for a given species in one season to that in another. Overall, the two species competed asymmetrically for space with R. l. velutinus competitively dominant over P. higginsi . In winter (June-October), competition was low, and it reached a maximum during the breeding season (November-April). In the dispersal period (March-May), intensity of competition decreased, but was still higher than in winter, as subadults entered the trappable population. Estimated competition coefficients are validated by analyzing residuals from those three seasons. Results indicate that competitive ability in ground-dwelling small mammals is correlated positively with habitat specialization, but both may be related to body size. Intensity of competition also depends on the population phase of competing species. Our findings suggest that the standardized regression technique can be used reliably to uncover community patterns.

Mosquito Consumption by Insectivorous Bats: Does Size Matter?

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.

Do mosquitoes influence bat activity in coastal habitats

Abstract Context. Conservation of insectivorous bat populations requires appropriate management of foraging habitats and the prey resources they sustain. Endangered coastal saltmarsh communities support a diverse range of aquatic and terrestrial arthropods, including the saltmarsh mosquito (Aedes vigilax Skuse), an important vector of mosquito-borne viruses and a potentially important prey resource for insectivorous bats. Prey detectability by bats is considered to be limited with low-frequency echolocation, particularly in cluttered habitats, that may render abundant Ae. vigilax populations unavailable to some bat species. Aims. To investigate relationships between availability of Ae. vigilax and non-mosquito prey, and the activity of foraging insectivorous bats in a range of coastal habitats. Methods. We measured nightly bat activity and the abundance of prey (mosquito and non-mosquito) concurrently during neap and spring tides in saltmarsh, urban and forest habitats. Comparisons were made between tidal cycle and habitats, and relationships between bat activity and the abundance of prey were examined. Key results. Whereas prey abundances were generally greatest in saltmarsh and forest habitats, bat activity was greatest in the forest habitat. However, proportional feeding activity was greatest in saltmarsh. Prey abundance was positively correlated with total bat activity only in the open saltmarsh, where an absence of clutter would maximise prey detectability and thus availability. Positive correlations between Ae. vigilax abundance and bat activity, across all habitats, were restricted to bats of the Vespadelus genus, which are small-sized bats that employ high-frequency echolocation suitable for detection of small prey along edges. Conclusions. These findings suggest that Ae. vigilax may be an important prey resource for small, high-frequency echolocating bats capable of discerning small prey within cluttered forest as well as exploiting abundant prey in the open saltmarsh. Implications. Small, high-frequency echolocating bats should be the focus of future studies investigating the importance of small prey, such as Ae. vigilax, to the diets of foraging bats.

Bassian bats in the Eyrean sub-region? Preliminary acoustic data from the Bogan and Macquarie Rivers in semi-arid NSW

We conducted acoustic surveys of insectivorous bat fauna in riparian areas along the Macquarie and Bogan River systems in the wheatbelt of semi-arid central-western New South Wales, Australia. In surveys of 10 sites we detected 11 species and two species groups of bats in eight genera. Four species, Chocolate Wattled Bat Chalinolobus morio, Large-footed Myotis Myotis macropus, Large Forest Bat Vespadelus darlingtoni and Southern Forest Bat V. regulus, are predominantly Bassian (chiefly coastal) in their recorded distributions but were detected in the semi-arid Eyrean sub-region on two rivers in vegetation dominated by River Red Gum Eucalyptus camaldulensis. The findings of this study highlight the need for further research to assess the importance of riparian corridors as habitat for insectivorous bats in semi-arid New South Wales.