Research Interests

Causes and consequences of dispersal in human modified-environments

Dispersal is a key process that (along with mortality and natality) shapes population growth and spatial pattern. Dispersal behaviour is an important factor in many of the environmental problems facing the world today (see Clobert et al. 2001). The capabilities of genetically modified crops to spread, increasing levels of resistance to insecticides amongst agricultural pests, invasion by exotic organisms and conservation of endangered plants and animals are all influenced by the dispersal patterns of the organism. Without a solid understanding of both dispersal patterns and factors that influence dispersal our ability to manage these problems is limited. The recent development of molecular techniques for measuring gene flow and dispersal allows many opportunities for research on organisms that are unsuitable for traditional mark-recapture techniques. Many of the research questions I am interested in relate to the causes and consequences of dispersal.

Photo: Theridiidae female with egg sac (A. O'Toole).

Evolutionary consequences of anthropogenic environmental change

With increasing fragmentation of habitats and global climate change the dispersal capabilities of an organism may be one of the most important factors in extinction risk (see Clobert et al. 2001). Many species exist in highly fragmented landscapes as a result of human activity. Metapopulation studies have shown that limited gene flow between isolated populations can result in morphological changes related to dispersal capability within a species (Thomas et al.1998, Hill et al. 1999). The specific questions I am interested in include:

• Are there other measurable traits, such as oviposition behaviour or life history characteristics that differ within a species as a result of selection pressures common in fragmented habitats?
• Do these changes allow the species to exist more successfully within fragmented habitats?
• Is there empirical evidence that animals can adapt to climate change by increasing their dispersal capabilities? For example: Are more winged aphid morphs produced under new or more variable climatic conditions (Denno & Peterson 2000, Roff 1986)?
• What are the implications for pest management in the future?

Biodiversity conservation outside of reserves

Small patches of remnant vegetation within an intensively managed region are often considered inadequate for use by bird and mammal species. These patches are often very small in size, characterised by high levels of disturbance and spatial isolation. The specific questions I am interested in include:

• Can these remnant vegetation patches in intensively managed matrix be useful for the conservation of invertebrate biodiversity?
• Does increased biodiversity within a region confer any benefits to land managers in terms of pest management or other measurable ecosystem services?
• Does the dispersal capability of a species (for spiders ballooners versus non-ballooners) limit gene flow between populations on remnants and how does this relate to spatial elements of the landscape?
• What are the implications for conservation and management of animals in fragmented habitats?

Arthropod predators, prey location and pest control: The influence of plant volatiles

There are many cues that predators use to locate prey in complex habitats such as the movement of prey, odours emitted from the prey and prey products (frass and silk) and information left from con-specifics. Some predatory arthropods have been shown to exploit volatile organic compounds emitted from plants in response to larval herbivore damage (Baldwin et al. 2001). The predatory mite Phytoseiulus persimilis Athias-Henriot is attracted to volatiles from bean plants infested with Spodoptera exigua (Hbn.) caterpillars despite the fact that it does not prey on this herbivore (Shimoda & Dicke 2000). Shimoda and Takabayashi (2001) demonstrated that a specialist staphylinid beetle predator responded to herbivore-induced plant volatiles from spider mite infested lime beans in both laboratory and field conditions. Similar responses have been demonstrated in generalist predators (Kessler & Baldwin 2001). Reddy (2002) found that the generalist predator Chrysoperla carenaStephens (Neuroptera: Chrysopidae) which preys on spider mites was attracted to volatiles emitted from mite-infested eggplant, okra and pepper leaves but not tomato leaves. This suggests that certain odour blends emitted by particular plants differ in their attractiveness to predators, and predators that may be able to use these cues to locate prey in one crop type may be unable to do so in other crop types. The specific questions I am interested in include:

• Do “specialist” and “generalist” arthropod predators use similar cues to locate prey in complex habitats?
• How do predators find stationary prey stages (such as Lepidoptera eggs) in the field?
• Do plant volatiles produced in response to oviposition have a role (see Hilker & Meiners 2002)?
• Does crop type affect the searching strategy of a predator and/or the plant volatiles they are attracted to?
• How important are herbivore induced plant volatiles for prey location in the field (in comparison to other cues)?

Photo: Thomisidae with captured bee in soybean.

Rarity and species conservation

The majority of ecological research is based on studies of abundant and widespread species (most of which are pest species). However, most sampling regimes result in the collection many rare species in comparison to one or a few more common species. The presence of ‘singletons’ plagues many population ecologists because they are time-consuming to sort and analyse, and their significance as part of the overall community is unknown. In many cases rare species are excluded from the analysis all together. This may in part be due to the inherent risks involved in studying a potentially rare species, illustrated by Britton and New (1995) who recorded only five individuals of a rare butterfly over three seasons of comprehensive surveys. Despite this constraint, greater emphasis must be placed on the study of rare species due to the link between rarity and increased extinction risk. The specific questions I am interested in include:

• What is the significance of rare species within an insect community?
• If these rare species were to become extinct what are the consequences for the entire plant and animal community?
• Are the community consequences of extinction influenced by the trophic position (herbivore, predators etc.) of the rare species?
• Some butterfly species have an abundant host plant but are still considered rare. Is dispersal between patches of host plant the primary determinant of patch occupancy? Or are factors related to patch quality more important?

Such questions could be tested via exclusion experiments that remove all or particular rare species and observe the change in the abundance of the remaining species. Conservation attempts should be made for any species at risk of extinction, but such experiments could give us some idea if more effort should be placed on those species whose extinction may cause significant flow on effects to the remaining community.

• Are the causes of rarity related to extinction risk?

Some species are considered to be naturally rare whilst others are rare as a result of human activity and were more common in the past. Gaston (1994) suggests that naturally rare species may be less prone to extinction because of adaptation over time. Laboratory experiments could be used to test this claim and such information could be useful in deciding on how funds for conservation plans should be distributed.

References

Baldwin IT, Halitschke R, Kessler A and Schittko U (2001) Merging molecular and ecological approaches in plant-insect interactions. Current Opinion in Plant Biology 4, 351-358.

Britton DR and New TR (1995) Rare Lepidoptera at Mount Piper, Victoria. The role of a threatened butterfly community in advancing understanding of insect conservation. Journal of the Lepidopterist’s Society 49(2), 97-113.

Clobert J, Danchin E, Dhondt A and Nichols JD (eds.) (2001) Dispersal. Oxford University Press, New York. (A comprehensive book on measurement, mechanisms and implications of dispersal for a variety of life forms).

Denno R and Peterson M (2000) Caught between the devil and the deep blue sea, mobile planthoppers elude natural enemies and deteriorating host plants. American Entomologist 46(2), 95-109.

Gaston KJ (1994) Rarity Chapman & Hall, London.

Hill, J. Thomas, C. and Lewis, O. (1999) Flight morphology in fragmented populations of a rare British butterfly, Hesperia comma. Biological Conservation 87, 277-283.

Hilker M and Meiners T (2002) Induction of plant responses to oviposition and feeding by herbivorous arthropods: A comparison. Entomologia Experimentalis et Applicata 104, 181-192.

Kessler A and Baldwin IT (2001) Defensive function of herbivore-induced plant volatile emissions in nature. Science 291, 2141-2144.

Thomas, C. Hill, J. and Lewis, O. (1998) Evolutionary consequences of habitat fragmentation in a localized butterfly. Journal of Animal Ecology 67, 485-497.

Reddy GV (2002) Plant volatiles mediate orientation and plant preference by the predator Chrysoperla carnea Stephens (Neuroptera: Chrysopidae). Biological Control 25, 49-55.

Roff D (1986) The evolution of wing dimorphism in insects. Evolution 40(5), 1009-1020.

Shimoda T and Dicke M (2000) Attraction of a predator to chemical information related to nonprey: When can it be adaptive? Behavioral Ecology 11, 606-613.

Shimoda T and Takabayashi J (2001) Response of Oligota kashmirica benefica, a specialist insect predator of spider mites, to volatiles from prey-infested leaves under both laboratory and field conditions. Entomologia Experimentalis et Applicata 101, 41-47.

Links

Arachnology sites

The International Society of Arachnology
The American Arachnology Society
The British Arachnology Society
The Wolf Spiders (Araneae, Lycosidae) of Australia by Volker W. Framenau

Entomology sites

The Australian Entomological Society
CSIRO Entomology
Entomological Society of America

Ecology sites

The Ecology Society of Australia
The Ecological society of America