Scope Of Insect Ecology

Insect ecology is the study of interactions between insects and their environment. Ecology is, by its nature, integrative, requiring the contributions of biologists, chemists, geologists, climatologists, soil scientists, geographers, mathematicians, and others to understand how the environment affects organisms, populations, and communities and is affected by their activities through a variety of feedback loops (Fig. 1.2). Insect ecology has both basic and applied goals. Basic goals are to understand and model these interactions and feedbacks (e.g., Price 1997). Applied goals are to evaluate the extent to which insect responses to environmental changes, including those resulting from anthropogenic activities, mitigate or exacerbate ecosystem change (e.g., Croft and Gutierrez 1991, Kogan 1998), especially in managed ecosystems.

Research on insects and associated arthropods (e.g., spiders, mites, centipedes, millipedes, crustaceans) has been critical to development of the fundamental principles of ecology, such as evolution of social organization (Haldane 1932, Hamilton 1964, E. Wilson 1973); population dynamics (Coulson 1979, Morris 1969, Nicholson 1958,Varley and Gradwell 1970,Varley et al. 1973,Wellington et al. 1975); competition (Park 1948, 1954); predator-prey interaction (Nicholson and Bailey 1935); mutualism (Batra 1966, Bronstein 1998, Janzen 1966, Morgan 1968, Rickson 1971, 1977); island biogeography (Darlington 1943, MacArthur and Wilson 1967, Simberloff 1969, 1978); metapopulation ecology (Hanski 1989); and regulation of ecosystem processes, such as primary productivity, nutrient cycling, and succession (Mattson and Addy 1975, J. Moore et al. 1988, Schowalter 1981, Seastedt 1984). Insects and other arthropods are small and

ECOSYSTEM CONDITIONS Climate Substrate Disturbances Vertical and horizontal structure Energy flow

COMMUNITY STRUCTURE Diversity

Species interactions Functional organization Ecological succession

INDIVIDUAL TRAITS Tolerance ranges Mobility

Resource acquisition Resource allocation

Biogeochemical cycling ^^ T ■

COMMUNITY STRUCTURE Diversity

Species interactions Functional organization Ecological succession

Density

Distribution

Genetic structure

Natality

Mortality

Dispersal

| Diagrammatic representation of feedbacks between various levels of ecological organization. Size of arrows is proportional to strength of interaction. Note that individual traits have a declining direct effect on higher organizational levels but are affected strongly by feedback from all higher levels.

easily manipulated subjects. Their rapid numeric responses to environmental changes facilitate statistical discrimination of responses and make them particularly useful models for experimental study. Insects also have been recognized for their capacity to engineer ecosystem change, making them ecologically and economically important.

Insects fill a variety of important ecological (functional) roles. Many species are key pollinators. Pollinators and plants have adapted a variety of mechanisms for ensuring transfer of pollen, especially in tropical ecosystems where sparse distributions of many plant species require a high degree of pollinator fidelity to ensure pollination among conspecific plants (Feinsinger 1983). Other species are important agents for dispersal of plant seeds, fungal spores, bacteria, viruses, or other invertebrates (Moser 1985, Nault and Ammar 1989, Sallabanks and Courtney 1992). Herbivorous species are particularly well-known as agricultural and forestry "pests," but their ecological roles are far more complex, often stimulating plant growth, affecting nutrient fluxes, or altering the rate and direction of ecological succession (MacMahon 1981, Maschinski and Whitham 1989, Mattson and Addy 1975, Schowalter and Lowman 1999, Schowalter et al. 1986, Trumble et al. 1993). Insects and associated arthropods are instrumental in processing of organic detritus in terrestrial and aquatic ecosystems and influence soil fertility and water quality (Kitchell et al. 1979, Seastedt and Crossley 1984). Woody litter decomposition usually is delayed until insects penetrate the bark barrier and inoculate the wood with saprophytic fungi and other microorganisms (Ausmus 1977, Dowding 1984, Swift 1977). Insects are important resources for a variety of fish, amphibians, reptiles, birds, and mammals, as well as for other invertebrate predators and parasites. In addition, some insects are important vectors of plant and animal diseases, including diseases such as malaria and plague, that have affected human and wildlife population dynamics.

The significant economic and medical or veterinary importance of many insect species is the reason for distinct entomology programs in various universities and government agencies. Damage to agricultural crops and transmission of human and livestock diseases has stimulated interest in, and support for, study of factors influencing abundance and effects of these insect species. Much of this research has focused on evolution of life history strategies, interaction with host plant chemistry, and predator-prey interactions as these contribute to our understanding of "pest" population dynamics, especially population regulation by biotic and abiotic factors. However, failure to understand these aspects of insect ecology within an ecosystem context undermines our ability to predict and manage insect populations and ecosystem resources effectively (Kogan 1998). Suppression efforts may be counterproductive to the extent that insect outbreaks represent ecosystem-level regulation of critical processes in some ecosystems.

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