Ecological selection
Encyclopedia
Ecological selection refers to natural selection
minus sexual selection
, i.e. strictly ecological processes that operate on a species
' 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.
In sexually reproducing
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.
For instance, Ceratogaulus, the Oligocene
horned gopher
, 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
, cities or zoos, where sexual selection
must generally predominate, as there is no threat of the species or individuals losing their ecological niche
. 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 has an impact on 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
, except in highly cognitive species that do not, or do not always, pair bond, e.g. walrus
, gorilla
, human
. 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
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
, 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
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.
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
minus sexual selection
Sexual selection
Sexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural selection...
, i.e. strictly ecological processes that operate on a species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
' 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.
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.In sexually reproducing
Sexual reproduction
Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...
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
Artificial selection
Artificial selection describes intentional breeding for certain traits, or combination of traits. The term was utilized by Charles Darwin in contrast to natural selection, in which the differential reproduction of organisms with certain traits is attributed to improved survival or reproductive...
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.
Ecological selection 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
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
horned gopher
Horned gopher
Horned gophers are rodents from the genus Ceratogaulus, a member of the extinct fossorial rodent family Mylagaulidae. Ceratogaulus is the only known rodent genus with horns, and is the smallest known horned mammal...
, 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
Built environment
The term built environment refers to the human-made surroundings that provide the setting for human activity, ranging in scale from personal shelter and buildings to neighborhoods and cities that can often include their supporting infrastructure, such as water supply or energy networks.The built...
, cities or zoos, where sexual selection
Sexual selection
Sexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural selection...
must generally predominate, as there is no threat of the species or individuals losing their ecological niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
. 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 has an impact on 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
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
, except in highly cognitive species that do not, or do not always, pair bond, e.g. walrus
Walrus
The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...
, gorilla
Gorilla
Gorillas are the largest extant species of primates. They are ground-dwelling, predominantly herbivorous apes that inhabit the forests of central Africa. Gorillas are divided into two species and either four or five subspecies...
, human
Human
Humans are the only living species in the Homo genus...
. 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
Sexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural selection...
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
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
, 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
Artificial selection
Artificial selection describes intentional breeding for certain traits, or combination of traits. The term was utilized by Charles Darwin in contrast to natural selection, in which the differential reproduction of organisms with certain traits is attributed to improved survival or reproductive...
. 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
Bikini Atoll
Bikini Atoll is an atoll, listed as a World Heritage Site, in the Micronesian Islands of the Pacific Ocean, part of Republic of the Marshall Islands....
, capacity to survive gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s to sexual maturity and (for the female) to term is a key ecological selection factor, although it is neither "natural
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
" nor sexual. Some would call this too artificial selection
Artificial selection
Artificial selection describes intentional breeding for certain traits, or combination of traits. The term was utilized by Charles Darwin in contrast to natural selection, in which the differential reproduction of organisms with certain traits is attributed to improved survival or reproductive...
, 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
Environment (biophysical)
The biophysical environment is the combined modeling of the physical environment and the biological life forms within the environment, and includes all variables, parameters as well as conditions and modes inside the Earth's biosphere. The biophysical environment can be divided into two categories:...
", and the term environmental selection may be preferable in these cases.