Ecology is the scientific study of the distribution and abundance of organisms, and how those organisms interact with each other and with their environment, which includes both living (e.g. competitors for food) and non-living (e.g. atmospheric nitrogen) components. Ecology relies upon and builds upon natural history, the careful observation and description of natural phenomenon but, as a science, ecology seeks to explain those observations in a way that allows extrapolation to novel situations.
Ecological questions often cannot be addressed in the same way that scientists would address other types of questions. In hypothetico-deductive scientific enquiry, carefully designed experiments are conducted so that empirical data can be used to reject alternative hypotheses until only one likely explanation is still plausible. However, in ecological research there are often too many uncontrollable variables for rigorous control and experimentation, so variables may interact in ways that cannot be detected through a reductionist approach. In addition to methodological concerns, the ecological question of interest may in fact not be whether factor A plays a role in producing observation B; the important question may ask how much influence factor A has on observation B, and whether this influence is the same across all levels of factors C, D, and E. One example of an ecological question not easily amenable to traditional hypothesis testing is the question: ‘Under current governmental regulations, how will polar bear reproduction be affected by noise associated with petroleum extraction?’ However, this type of question can be addressed with mathematical models built upon the answers to questions such as: ‘What is the hearing range of female polar bears?’
Ecology is a historical science; current patterns and processes have been shaped by evolution, past stochastic events and ongoing responses to current conditions. For example, the distribution of the cattle egret has changed dramatically since its colonization of North America several decades ago, but that colonization would not have been successful without traits the egret possessed due to past natural selection. As a consequence of egret colonization, current survival rates of some North American grasshoppers may now depend on whether past predation by other bird species has shaped grasshopper anti-predator behaviour that coincidentally thwarts hungry egrets.
Ecologists study questions at various levels of organization and complexity, from broad enquiries spanning the entire biosphere (e.g. the water cycle) to enquiries that focus on individual organisms (e.g. the seasonality of reproduction). Each level of organization exhibits properties not apparent at lower levels of organization, but dependent on characteristics of those smaller units (e.g. genetic differences among neighbouring populations can be influenced by dispersal of individuals). Ecologists sometimes consider the operation and impact of small-scale factors on individuals, but ecologists typically focus on questions regarding larger scales - individuals, populations, communities and ecosystems. A population is the group of potentially interbreeding individuals of the same species. Population ecologists seek to understand the factors determining the rate at which individuals are born, reproduce and die, and how changes in those rates alter the size of the population. An ecological community is comprised of the populations of different species that interact with each other in a particular habitat. Community ecologists seek to understand interactions between species, species diversity and persistence and community productivity. Landscape ecologists strive to understand the spatial and temporal heterogeneity of communities, while ecosystem ecologists investigate the interactions of communities of organisms and their abiotic environments.
An ecologist might specialize in using certain methodologies to address questions (e.g. molecular ecologists) or focus on specific types of each level of organization (e.g. freshwater ecologists). Although many subdisciplines of ecology have relevance for applied animal behaviour and welfare, several subdisciplines are particularly relevant. Agroecologists apply ecological knowledge in the development of sustainable agricultural practices, including animal husbandry. Conservation ecologists strive to restore and maintain long-term functional levels of biodiversity. Disease ecologists attempt to understand and control the factors contributing to the spread of diseases. Ecotoxicologists endeavour to identify and minimize the impact of chemical and biological pollutants at various ecological levels, including the physiology of individuals. Sensory ecologists investigate the way in which animals receive and respond to information about their environment, which may guide human efforts to maintain species-typical psychological, physiological and reproductive processes in a captive or domestic setting. Urban ecologists seek to identify how human cities alter ecological processes: the preservation and restoration of undeveloped habitats; the degree to which those habitats are connected; and the levels of environmental pollutants that determine which species persist in urban areas. Wildlife managers traditionally focused on the management of populations of free-ranging animals for sustainable human consumption, but now utilize population and habitat management for the broader conservation of biodiversity.
As an example of the application of ecological principles, consider the alteration of carrying capacity in the conservation of eastern bluebird populations in North America. The carrying capacity for an organism is the population size that can be sustained in a given patch of habitat. The ecological factor(s) limiting an animal’s carrying capacity may be food, water, shelter, refuges from predators or breeding sites. Modifying the factor limiting the carrying capacity can be one way to alter a population’s size, for better or worse. Populations of eastern bluebirds increased dramatically as native forests were converted into fields suitable for bluebird foraging adjacent to wooden fences providing nesting cavities. Through the early 1900s, however, competition with introduced competitors for nesting cavities, replacement of wooden fences with metal fences and pesticide use reduced the carrying capacity and populations of eastern bluebirds. Subsequent widespread installation of thousands of birdhouses designed specifically for eastern bluebirds increased carrying capacity throughout large areas, which resulted in rebounding bluebird populations.
From an applied standpoint there is increasing recognition that, although ecology developed from a descriptive field into an explanatory field, ecologists must now also predict how organisms will fare under conditions that ecologists have never seen and organisms have never experienced. Human activities such as hunting, fishing and farming were made possible by the types of observations that underlie ecology; the ongoing challenge for ecologists is to understand and address the ecological ramifications of increasing human resource use.
see also: Behavioural ecology; Biodiversity; Conservation; Dispersal and habitat selection; Ecological niche; Home range; Territoriality; Translocation; Wildlife management
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