Philopatry

Philopatry is the tendency of an organism to stay in or habitually return to a particular area. The causes of philopatry are numerous, but natal philopatry, where animals return to their birthplace to breed, may be the most common. The term derives from the Greek 'home-loving', although in recent years the term has been applied to more than just the animal's birthplace. Recent usage refers to animals returning to the same area to breed despite not being born there, and migratory species that demonstrate site fidelity: reusing stopovers, staging points, and wintering grounds. Some of the known reasons for organisms to be philopatric would be for mating (reproduction), survival, migration, parental care, resources, etc.. In most species of animals, individuals will benefit from living in groups, because depending on the species, individuals are more vulnerable to predation and more likely to have difficulty finding resources and food. Therefore, living in groups increases a species chances of survival, which correlates to finding resources and reproducing. Again, depending on the species, returning to their birthplace where that particular species occupies that territory is the more favorable option. The birthplaces for these animals serve as a territory for them to return for feeding and refuge, like fish from a coral reef. In an animal behavior study conducted by Paul Greenwood, overall female mammals are more likely to be philopatric, while male mammals are more likely to disperse. Male birds are more likely to philopatric, while females are more likely to disperse. Philopatry will favor the evolution of cooperative traits because the direction of sex has consequences from the particular mating system. Philopatry is the tendency of an organism to stay in or habitually return to a particular area. The causes of philopatry are numerous, but natal philopatry, where animals return to their birthplace to breed, may be the most common. The term derives from the Greek 'home-loving', although in recent years the term has been applied to more than just the animal's birthplace. Recent usage refers to animals returning to the same area to breed despite not being born there, and migratory species that demonstrate site fidelity: reusing stopovers, staging points, and wintering grounds. Some of the known reasons for organisms to be philopatric would be for mating (reproduction), survival, migration, parental care, resources, etc.. In most species of animals, individuals will benefit from living in groups, because depending on the species, individuals are more vulnerable to predation and more likely to have difficulty finding resources and food. Therefore, living in groups increases a species chances of survival, which correlates to finding resources and reproducing. Again, depending on the species, returning to their birthplace where that particular species occupies that territory is the more favorable option. The birthplaces for these animals serve as a territory for them to return for feeding and refuge, like fish from a coral reef. In an animal behavior study conducted by Paul Greenwood, overall female mammals are more likely to be philopatric, while male mammals are more likely to disperse. Male birds are more likely to philopatric, while females are more likely to disperse. Philopatry will favor the evolution of cooperative traits because the direction of sex has consequences from the particular mating system. One type of philopatry is breeding philopatry, or breeding-site fidelity, and involves an individual, pair, or colony returning to the same location to breed, year after year. Among animals that are largely sedentary, breeding-site philopatry is common. It is advantageous to reuse a breeding site, as there may be territorial competition outside of the individual’s home range, and since the area evidently meets the requirements of breeding. Such advantages are compounded among species that invest heavily in the construction of a nest or associated courtship area. For example, the megapodes (large, ground-dwelling birds such as the Australian malleefowl, Leipoa ocellata) construct a large mound of vegetation and soil or sand to lay their eggs in. Megapodes often reuse the same mound for many years, only abandoning it when it is damaged beyond repair, or due to disturbance. Nest fidelity is highly beneficial as reproducing is time and energy consuming (malleefowl will tend a mound for five to six months per year). In colonial seabirds, it has been shown that nest fidelity depends on multi-scale information, including the breeding success of the focal breeding pair, the average breeding success of the rest of the colony, and the interaction of these two scales. Breeding fidelity is also well documented among species that migrate or disperse after reaching maturity. Birds, in particular, that disperse as fledglings will take advantage of exceptional navigational skills to return to a previous site. Philopatric individuals exhibit learning behaviour, and do not return to a location in following years if a breeding attempt is unsuccessful. The evolutionary benefits of such learning are evident: individuals that risk searching for a better site will not have lower fitness than those that persist with a poor site. Philopatry is not homogenous within a species, with individuals far more likely to exhibit philopatry if the breeding habitat is isolated. Similarly, non-migratory populations are more likely to be philopatric that those that migrate. In species that exhibit lifelong monogamous pair bonds, even outside of the breeding season, there is no bias in the sex that is philopatric. However, among polygynous species that disperse (including those that find only a single mate per breeding season), there is a much higher rate of breeding-site philopatry in males than females among birds, and the opposite bias among mammals. Many possible explanations for this sex bias have been posited, with the earliest accepted hypothesis attributing the bias to intrasexual competition, and territory choice. The most widely accepted hypothesis is that proposed by Greenwood (1980). Among birds, males invest highly in protecting resources – a territory – against other males. Over consecutive seasons, a male that returns to the same territory has higher fitness than one that is not philopatric. Females are free to disperse, and assess males. Conversely, in mammals, the predominant mating system is one of matrilineal social organisation. Males generally invest little in the raising of offspring, and compete with each other for mates rather than resources. Thus dispersing can result in reproductive enhancement, as greater access to females is available. On the other hand, the cost of dispersal to females is high, and thus they are philopatric. This hypothesis also applies to natal philopatry, but is primarily concerned with breeding-site fidelity. A more recent hypothesis builds on Greenwood’s findings, suggesting that parental influence may play a large role. Because birds lay eggs, adult females are at risk of being cuckolded by their daughters, and thus would drive them out. On the other hand, young male mammals pose a threat to their dominant father, and so are driven to disperse while young. This page discusses the evolutionary reasons for philopatry. For the mechanisms of philopatry, see Natal homing Natal philopatry commonly refers to the return to the area the animal was born in, or to animals remaining in their natal territory. It is a form of breeding-site philopatry. The debate over the evolutionary causes remains unsettled. The outcomes of natal philopatry may be speciation, and, in cases of non-dispersing animals, cooperative breeding. Natal philopatry is the most common form of philopatry in females because it decreases competition for mating and increases the rate of reproduction and a higher survival rate for offspring. Natal philopatry also leads to a kin-structured population, which is when the population is more genetically related than less related between individuals in a species. This can also lead to inbreeding and a higher rate of natural and sexual selection within a population. The exact causes for the evolution of natal philopatry are unknown. Two major hypotheses have been proposed. Shields (1982) suggested that philopatry was a way of ensuring inbreeding, in a hypothesis known as the optimal-inbreeding hypothesis. He argued that, since philopatry leads to the concentration of related individuals in their birth areas, and thus reduced genetic diversity, there must be some advantage to inbreeding – otherwise the process would have been evolutionary detrimental and would not be so prevalent. The major beneficial outcome under this hypothesis is the protection of a local gene complex that is finely adapted to the local environment. Another proposed benefit is the reduction the cost of meiosis and recombination events. Under this hypothesis, non-philopatric individuals would be maladapted and over multi-generational time, philopatry within a species could become fixed. Evidence for the optimal-inbreeding hypothesis is found in outbreeding depression. Outbreeding depression involves reduced fitness as a result of random mating, which occurs due to the breakdown of coadapted gene complexes by combining allele that do not cross well with those from a different subpopulation. However, it is important to note that outbreeding depression becomes more detrimental the longer (temporally) that subpopulations have been separated, and that this does hypothesis does not provide an initial mechanism for the evolution of natal philopatry. A second hypothesis explains the evolution of natal philopatry as a method of reducing the high costs of dispersal among offspring. A review of records of natal philopatry among passerine birds found that migrant species showed significantly less site fidelity than sedentary birds. Among migratory species, the cost of dispersal is paid either way. If the optimal-inbreeding hypothesis was correct, the benefits of inbreeding should result in philopatry among all species. Inbreeding depression is a phenomenon whereby deleterious alleles become fixed more easily within an inbreeding population. Inbreeding depression is demonstrably costly and accepted by most scientists as a greater cost than those of outbreeding depression. Within a species, there has also been found to be variation in rates of philopatry, with migratory populations exhibiting low levels of philopatry – further suggesting that the ecological cost of dispersal, rather than genetic benefits of either inbreeding or outbreeding, is the driver of natal philopatry.