Ecological Selection
   HOME

TheInfoList



OR:

Ecological selection (or environmental selection or survival selection or individual selection or asexual selection) refers to
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Cha ...
without
sexual selection Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex (in ...
, i.e. strictly ecological processes that operate on a
species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
' inherited traits without reference to mating or secondary sex characteristics. The variant names describe varying circumstances where sexual selection is wholly suppressed as a mating factor. Ecologists often study ecological selection when examining the abundance of individuals per population across regions, and what governs such abundances.


Circumstances in which it occurs

Ecological selection can be said to be taking place in any circumstance where inheritance of specific traits is determined by ecology alone without direct sexual competition, when e.g. sexual competition is strictly ecological or economic, there is little or no mate choice, females do not resist any male who wishes to mate, all traits will be equally propagated regardless of mating, or the species is hermaphroditic or asexually reproducing, an ecological selection is taking place. For example, environmental pressures are largely responsible for the evolution of different life history strategies between the African honey bee, ''A. m. scutellata'', and the European honey bee. In
sexually reproducing Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...
species, it is applicable mostly to situations where ecological pressures prevent most competitors from reaching maturity, or where crowding or pair-bonding or an extreme suppression of sexual selection factors prevents the normal sexual competition rituals and selection from taking place, but which also prevent artificial selection from operating, e.g. arranged marriages, where parents rather than the young select the mate based on economic or even astrological factors, and where the sexual desires of the mated pair are often subordinated to these factors, are artificial unless ''wholly'' based on an ecological factor such as control of land which is held by their own force. In forests, ecological selection can be witnessed involving many factors such as available sunlight, soil quality, and the surrounding
biota Biota may refer to: * Biota (ecology), the plant and animal life of a region * Biota (plant), common name for a coniferous tree, ''Platycladus orientalis'' * Biota, Cinco Villas, a municipality in Aragon, Spain * Biota (band), a band from Color ...
. During forest growth, tree seedlings in particular, are ecosystem pioneers, and different tree seedlings can often react to a number of members in their ecological community in completely different ways, thus providing a spectrum of ecological occupations. On the other hand, adult trees can heavily impact their ecological communities, reversing the roles of ecological selection. Elements of the soil are an extremely influential selective factor in forest growth. Throughout time, every species of tree has evolved to grow under specific soil conditions, whether it is dependent on the pH levels, the mineral contents, or the drainage levels. Each of these is a vehicle for ecological selection to do its work in the course of
evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
. However, ecological selection can be much more specific, not only working within species but within populations, even populations in the same region. For example, scientists in
Quebec Quebec ( ; )According to the Government of Canada, Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is ...
recently examined how tree seedlings react to different nitrate levels. What they found was that areas with higher nitrate levels contained plants that could much more efficiently metabolize nitrogen. Such plants could perform
photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
and respiration at a much faster rate than their nitrogen lacking peers, and also had longer root lengths on average, giving them an evolutionary advantage for their
habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
. Nitrogen levels that are unexpectedly too high could harm some tree species, but these particular specimens created a niche for themselves, and could outcompete others around them. A site of tree growth can also be influenced by slope, rockiness, climate, and available sunlight. Space is initially available to everything, but seedlings that can most quickly inhabit the soil and take advantage of the available nutrients are usually most successful. Generally, one of the first factors to control which species grow best in the soil is the amount of sunlight. Soil and water themselves are both very important (For instance, a dry hardwood such as a white oak will not grow in a swamp), but sunlight is the initial decider in forest succession. Shade intolerant trees can immediately grow impressively. They need the sunlight that is offered by an open canopy found in a bare environment. Selection weeds out the seedlings that can not handle full sun, thus tall, straight trees will eventually grow and develop a full, lush canopy. However, these behaviors will soon be reversed. Seedlings that were once removed by ecological selection now become favored, because the shaded forest floor has become ideal for such shade tolerant species. This is a great example of how ecological selection can create niches for different species by performing the same function with different outcomes.


Vs. sexual selection

In cases where ecological and sexual selection factors are strongly at odds, simultaneously encouraging and discouraging the same traits, it may also be important to distinguish them as sub-processes within natural selection. For instance, ''Ceratogaulus'', the
Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but ...
horned gopher Horned gophers are extinct rodents from the genus ''Ceratogaulus'', a member of the extinct fossorial rodent clade Mylagaulidae. ''Ceratogaulus'' is the only known rodent genus with horns, and is the smallest known horned mammal. ''Ceratogaulus' ...
, left in the fossil record a series of individuals with successively longer and longer horns, that seemed to be unrelated or maladaptive to its ecological niche. Some modern scientists have theorized that the horns were useful or impressive in mating rituals among males (although other scientists dispute this theory, pointing out that the horns were not sexually dimorphic) and that it was an example of runaway evolution. The species seems to have suddenly died out when horns reached approximately the body length of the animal itself, possibly because it could no longer run or evade predators—thus ecological selection seems to have ultimately trumped sexual. It is also important to distinguish ecological selection in cases of extreme ecological abundance, e.g. the human
built environment The term built environment refers to human-made conditions and is often used in architecture, landscape architecture, urban planning, public health, sociology, and anthropology, among others. These curated spaces provide the setting for human ...
, cities or zoos, where
sexual selection Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex (in ...
must generally predominate, as there is no threat of the species or individuals losing their
ecological niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of resources and competitors (fo ...
. Even in these situations, however, where survival is not in question, the variety and the quality of food, e.g. as presented by male to female monkeys in exchange for sex in some species, still influences reproduction, however it becomes a sexual selection factor. Similar phenomena can be said to exist in humans e.g. the " mail order bride" who primarily mates for economic advantage. Differentiating ecological selection from sexual is useful especially in such extreme cases; Above examples demonstrate exceptions rather than a typical selection in the wild. In general, ecological selection is assumed to be the dominant process in
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Cha ...
, except in highly cognitive species that do not, or do not always, pair bond, e.g.
walrus The walrus (''Odobenus rosmarus'') is a large flippered marine mammal with a discontinuous distribution about the North Pole in the Arctic Ocean and subarctic seas of the Northern Hemisphere. The walrus is the only living species in the f ...
,
gorilla Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four ...
,
human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
. But even in these species, one would distinguish cases where isolated populations had no real choice of mates, or where the vast majority of individuals died before sexual maturity, leaving only the ecologically selected survivor to mate—regardless of its sexual fitness under normal
sexual selection Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex (in ...
processes for that species. For example, if only a few closely related males survive a natural disaster, and all are able to mate very widely due to lack of males, sexual selection has been suppressed by an ecological selection (the disaster). Such situations are usually temporary, characteristic of populations under extreme stress, for relatively short terms. However, they can drastically affect populations in that short time, sometimes eliminating all individuals susceptible to a
pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a ger ...
, and thereby rendering all survivors immune. A few such catastrophic events where ecological selection predominates can lead to a population with specific advantages, e.g. in colonization when invading populations from more crowded disease-prone conditions arrive with antibodies to diseases, and the diseases themselves, which proceed to wipe out natives, clearing the way for the colonists. In humans, the intervention of artificial devices such as ships or blankets may be enough to make some consider this an example of artificial selection. However it is clearly observed in other species, it seems unreasonable to differentiate colonization by ship from colonization by walking, and even the word "colony" is not specific to humans but refers generically to an intrusion of one species on an ecology to which it has not wholly adapted. So, despite the potential controversy, it may be better to consider all examples of colonist-borne diseases to be ecological selection. For another example, in a region devastated by nuclear radiation, such as the Bikini Atoll, capacity to survive
gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nucleus, atomic nuclei. It consists of the shortest wavelength electromagnetic wav ...
s to sexual maturity and (for the female) to term is a key ecological selection factor, although it is neither " natural" nor sexual. Some would call this too artificial selection, not natural or ecological, as the radiation does not enter the ecology as a factor save due to man's effort. Ambiguous artificial-plus-ecological factors may reasonably be called " environmental", and the term environmental selection may be preferable in these cases.


See also

*
Ecology 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 overl ...


References

{{DEFAULTSORT:Ecological Selection Ecological processes Selection Population genetics