Ecology is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps with the closely related sciences of biogeography, evolutionary biology, genetics, ethology, and natural history. Ecology is a branch of biology, and it is not synonymous with environmentalism.
In ecology, a niche is the match of a species to a specific environmental condition. It describes how an organism or population responds to the distribution of resources and competitors and how it in turn alters those same factors. "The type and number of variables comprising the dimensions of an environmental niche vary from one species to another [and] the relative importance of particular environmental variables for a species may vary according to the geographic and biotic contexts".
Biogeography is the study of the distribution of species and ecosystems in geographic space and through geological time. Organisms and biological communities often vary in a regular fashion along geographic gradients of latitude, elevation, isolation and habitat area. Phytogeography is the branch of biogeography that studies the distribution of plants. Zoogeography is the branch that studies distribution of animals. Mycogeography is the branch that studies distribution of fungi, such as mushrooms.
In biology, coevolution occurs when two or more species reciprocally affect each other's evolution through the process of natural selection. The term sometimes is used for two traits in the same species affecting each other's evolution, as well as gene-culture coevolution.
Sexual reproduction is an adaptive feature which is common to almost all multicellular organisms and various unicellular organisms, with some organisms being incapable of asexual reproduction. Currently the adaptive advantage of sexual reproduction is widely regarded as a major unsolved problem in biology. As discussed below, one prominent theory is that sex evolved as an efficient mechanism for producing variation, and this had the advantage of enabling organisms to adapt to changing environments. Another prominent theory, also discussed below, is that a primary advantage of outcrossing sex is the masking of the expression of deleterious mutations. Additional theories concerning the adaptive advantage of sex are also discussed below. Sex does, however, come with a cost. In reproducing asexually, no time nor energy needs to be expended in choosing a mate. And if the environment has not changed, then there may be little reason for variation, as the organism may already be well adapted. Sex also halves the amount of offspring a given population is able to produce. Sex, however, has evolved as the most prolific means of species branching into the tree of life. Diversification into the phylogenetic tree happens much more rapidly via sexual reproduction than it does by way of asexual reproduction.
Evolutionary game theory (EGT) is the application of game theory to evolving populations in biology. It defines a framework of contests, strategies, and analytics into which Darwinian competition can be modelled. It originated in 1973 with John Maynard Smith and George R. Price's formalisation of contests, analysed as strategies, and the mathematical criteria that can be used to predict the results of competing strategies.
Leigh Van Valen was a U.S. evolutionary biologist. At the time of his death, he was professor emeritus in the Department of Ecology and Evolution at the University of Chicago.
Species richness, or biodiversity, increases from the poles to the tropics for a wide variety of terrestrial and marine organisms, often referred to as the latitudinal diversity gradient. The latitudinal diversity gradient is one of the most widely recognized patterns in ecology. It has been observed to varying degrees in Earth's past. A parallel trend has been found with elevation, though this is less well-studied.
The turnover-pulse hypothesis, formulated by paleontologist Elisabeth Vrba, suggests that major changes to the climate or ecosystem often result in a period of rapid extinction and high turnover of new species across multiple different lineages. Changes may include climate change, tectonic plate shifting, and catastrophes, among other things. It can be seen as an extension of the concept of evolutionary radiation from a single to a multi-clade context.
Elisabeth S. Vrba is a paleontologist at Yale University who developed the turnover-pulse hypothesis.
The following outline is provided as an overview of and topical guide to ecology:
In philosophy of science, strong inference is a model of scientific inquiry that emphasizes the need for alternative hypotheses, rather than a single hypothesis to avoid confirmation bias.
The Red Queen hypothesis is a hypothesis in evolutionary biology proposed in 1973, that species must constantly adapt, evolve, and proliferate in order to survive while pitted against ever-evolving opposing species. The hypothesis was intended to explain the constant (age-independent) extinction probability as observed in the paleontological record caused by co-evolution between competing species; however, it has also been suggested that the Red Queen hypothesis explains the advantage of sexual reproduction at the level of individuals, and the positive correlation between speciation and extinction rates in most higher taxa.
Many species have multiple sexual ornaments, whereby females select mating partners using several cues instead of only one cue. Whereas this phenomenon is self-evident and hence long recognized, adaptive explanations of why females use several instead of only one signal have been formulated relatively recently. Several hypotheses exist, but mutually exclusive tests are still lacking.
Host–parasite coevolution is a special case of coevolution, where a host and a parasite continually adapt to each other. This can create an evolutionary arms race between them. A more benign possibility is of an evolutionary trade-off between transmission and virulence in the parasite, as if it kills its host too quickly, the parasite will not be able to reproduce either. Another theory, the Red Queen hypothesis, proposes that since both host and parasite have to keep on evolving to keep up with each other, and since sexual reproduction continually creates new combinations of genes, parasitism favours sexual reproduction in the host.
Ecological fitting is "the process whereby organisms colonize and persist in novel environments, use novel resources or form novel associations with other species as a result of the suites of traits that they carry at the time they encounter the novel condition". It can be understood as a situation in which a species' interactions with its biotic and abiotic environment seem to indicate a history of coevolution, when in actuality the relevant traits evolved in response to a different set of biotic and abiotic conditions.
Escape and radiate coevolution is a hypothesis proposing that a coevolutionary 'arms-race' between primary producers and their consumers contributes to the diversification of species by accelerating speciation rates. The hypothesized process involves the evolution of novel defenses in the host, allowing it to "escape" and then "radiate" into differing species.
Fluctuating selection is a mode of natural selection characterized by the fluctuation of the direction of selection on a given phenotype over a relatively brief period of evolutionary time. For example, a species of plant may come in two varieties: one which prefers wetter soil and one which prefers dryer soil. During a period of wet years, the wet variety will be more fit and produce more offspring, and thereby increase the frequency of wet-preferring plants. If this wet period is followed by drought, the dry variety will be selected for and its numbers will increase. As periods of dryness and wetness fluctuate, so too does selection on dry-preferring and wet-preferring plants. Fluctuating selection is also manifest at the genic level. Consider two alleles, A and B, which are found at the same locus. Fluctuating selection dynamics are at play when selection favors A at time t0, B at t1 and A again at t2.
The sloshing bucket model of evolution is a theory in evolutionary biology that describes how environmental disturbances varying in magnitude will affect the species present. The theory emphasizes the causal relationship between environmental factors that impinge and affect genealogical systems, providing an overarching view that determines the relationship between the variety of biological systems.
The Red King hypothesis is the opposite idea to the Red Queen hypothesis, where mutualistic and symbiotic interactions favor the fitness of a set of individuals through slow evolution, as opposed to having competitive interactions or having an "arms race". It has been described that individuals from different communities can establish positive interactions for long periods of time when there is a great benefit for both parties, also through mutual help, individuals from different species (communities) can share different tasks to build a niche, which avoid spending energy in competing and increasing their resilience over environmental stress.
