Site fidelity

Dispersal

DEFINITION: the action or process of distributing or spreading things (e.g. seeds) or animals (including people) over a wide area.

All species disperse to some extent, and the rate of the dispersal differs between the species. It is the process that strongly influences the population dynamics of a species, helping to regulate population size and density. For examples, some aphids increase their dispersal rates under high density conditions but some grasshoppers may experience higher dispersal rates while experiencing low density (e.g. it may happen during an expansion process at peripheral populations where density is lower density than in central populations).

Dispersal can have large effects on neighboring populations. Marginal populations that are subject to high rates of immigration may experience a rescue effect, where despite poor genetic or ecological conditions, populations are able to persist. On the other hand, high dispersal rates can inhibit adaptation to novel environments due to constant influx of nonadapted individuals. Small populations that experience high rates of emigration may have a higher probability of extinction under such situations.

Dispersion is an effect of resources becoming limited locally as populations grow (density dependent dispersal) - individuals must find vital recources that may be absent in situ. So it may be a favorable option, when it 1) can buffer against temporal variation and spatial asynchrony in habitat quality (resource competition hypothesis, Greenwood 1980). Besides, dispersion decreases inter-individual competion for resources (where resources could be mates, food, and/or territory). Finally, dispersion is an important evolutionary event since it imposes gene flow from one population to another, so it shapes genetic differentiation of the population (also reducint the risk of inbreeding depression), and local adaptations.

A reverse of disepersal is being faithful to a site (site fidelity), and it can also be beneficial. It may 1) increase the likelihood of finding suitable breeding habitat and mates, 2) increase familiarity with local conditions, 3) increase the chance to mate with locally adapted individuals, this way reducing costs of genetic recombination, 4) increase the chance to remate with a former breeding partner (benefit of pair experience), and 5) help to avoid potential costs related to movement and to settlement in a new area.

Two types of dispersal are commonly distinguished: natal dispersal, which is a movement and subsequent breeding away from the birth territory or area, and breeding dispersal, which is a movement from one area to another after the first breeding season.

Natal dispersal

Natal dispersal is when juveniles undergo permanent dispersal to another location. Natal dispersion typically covers larger distances than breeding dispersal. Individuals that return to their natal habitat are philopatric, and often show life-long site fidelity to the first breeding location. Natal dispersal is often sex-biased.

Breeding dispersal

For all interoparus species (with multiple breeding attempts) breeding dispersal can occur throughout life and each adult must decide whether or not to disperse to a new breeding site at the beginning of each breeding season.

Breeding dispersal (as natal) is often strongly sex-dependent, and although we do not yet fully understand why one sex is more dispersal than the other in given species, multiple hypotheses suggest that this is because the two sexes differ in resource limitation, mating opportunities, competitive ability, morphological capacity to disperse, or even in the genetic basis of dispersal. These sexual asymmetries vary with the social mating system and the intensity of sexual selection, and are linked to the level of sex bias in breeding dispersal.

There could various examples here but the most evoked ones, that also create kind of pattern, are birds and mammals. In birds, females seem to be in general more likely to undergo dispersal whereas in mammals, males are the sex that is more likely to disperse. As dispersal could be beneficial as a mean to avoid inbreeding, the observed difference in the natal dispersal in birds and mammals is likely to be related to the patterns of mating system. In socially monogamous systems, as typically in birds, males often defend resources to gain mating opportunities (but see Trochet et al. 2016) and are less likely to disperse than females, whereas in polygynous systems, as typically in mammals, the sex being pursued (i.e., female) is less likely to disperse (Greenwood 1980).

Table from Trochet et al 2016.

Several theoretical hypotheses have been proposed to explain the evolution of sex-biased dispersal: the resource competition hypothesis (Greenwood 1980), the local mate competition hypothesis, and the inbreeding avoidance hypothesis. Sociality and the presence of handicap in sexes (epigametic traits or parental care) have also been proposed to be linked with the direction of this bias (Perrin and Goudet 2001). Those hypotheses argued that the mating system should be the major factor explaining the direction of such bias. Recent Trochet et al (2016) systematic review marginally corroborates Greenwood’s hypothesis, and shows strong relationships between the direction of sex-biased dispersal, mating systems, and territoriality. More importantly, the results of Trochet at al (2016) study highlights that the evolution of this bias was more linked to parental care and sexual dimorphism. These traits were also found to be associated with mating systems, suggesting that sexual asymmetry in morphology and parental care might be the main determinant of the evolution of sex-biased dispersal across species and not mating systems per se.

From Trochet et al 2016.

Site fidelity - a case study

Kwon et al (2022) related overall site fidelity and sex bias in site fidelity to two variables that reflect the intensity of sexual selection—the social mating system and sexual size dimorphism and used shorebirds as a study system.

From Szekeley et al 2006.

N species = 49 (111 populations). Breeding site fidelity varies a lot (0-100%). Monogamous species show higher breeding site fidelity than polyandrous and polygynous species. (Kwon et al 2022).

Overall, a strong male bias in return rates, but the sex-bias in return rate was independent of the mating system and did not covary with the extent of sexual size dimorphism. (Kwon et al 2022).

Thus, there is correlation of dispersal rate with the mating system but it is regardless of sex. This suggests that breeding site fidelity may be linked to mate fidelity, which is only important in the monogamous, biparentally incubating species, or that the same drivers influence both the mating system and site fidelity. The strong connection between site fidelity and the mating system suggests that variation in site fidelity may have played a role in the coevolution of the mating system, parental care, and migration strategies (Kwon et al 2022).

Predictability of environment

Site fidelity should be inversely related to heterogeneity in territory quality and the animal’s lifespan and positively related to the cost of changing territories, age and probability of mortality in the habitat (Switzer 1993). The predictability of reproductive outcome (i.e. probability that next period’s outcome will be the same as this period’s outcome) also affects site fidelity.

In predictable habitats, changing territories may be favoured after a bad previous outcome. In contrast, settlement should be independent of the previous outcome in unpredictable habitats.

Two potential strategies (decision rules): always stay and win-stay: lose-switch; optimal strategy under certain conditions. The always stay strategy does well in unpredictable habitats, when the mean quality within a territory is equal among territories. In contrast, the win-stay: lose-switch strategy performs best in predictable habitats.

Site fidelity evolving in response to natural conditons is adaptive behaviour. However, with rapid environmental changes, site fidelity may be maladaptive. It may much depend on the time-scale in which the site fidelity is exhibited. Within years, site fidelity can be affected by short- term environmental changes (such as extreme weather events, release of dam water, or severe fires caused by fire suppression regimes). Inter-annual site fidelity can be affected by increasing environmental variation (for example, more frequent or more intense swings between climatic phases). Perhaps the most detrimental impacts result from long- term, monotonic changes (such as climate warming and land- cover change); Merkle et al 2022.

From Merkle et al 2022.

Strong site fidelity may be maladaptive. A good example is american population of mule deer (Odocoileus hemionus). In a natural gas field development in western Wyoming (US), available habitat for overwintering mule deers has decreased over the past two decades. The cumulative amount of habitat converted to roads and well pads within the gas field has increased. Although this population of mule deer has made fine-scale behavioral changes to avoid habitat close to human infrastructure during winter, individuals exhibited strong site fidelity to their winter range prior to development; in the subsequent decades, the mule deer popula- tion has fallen by 40%. After Merkle et al 2022.

From Merkle et al 2022.

Another strong site fidelity example, with its maladaptive performance are northern elephant seals (Mirounga angustirostris). Many females exhibit strong site fidelity to foraging habitats in the North Pacific Ocean during their migrations. Tagging data spanning ~7000 km for the same individual in 1995 and 2006 ilustrates this well. Quantifying individual-level site fidelity and performance metrics over 10 years revealed that elephant seals with strong site fidelity performed best in average climate conditions, outperforming those that lacked site fidelity. However, this pattern was reversed during anomalous climate conditions. Because migration performance is directly linked to reproductive success in northern elephant seals, increasing climate variability projected in the North Pacific may influence the evolutionary benefit of site fidelity to this species. After Merkle et al 2022.

From Merkle et al 2022.

Site fidelity - miscellaneous

Foraging of kittiwakes

Site fidelity may be related to the breeding site, and that is the most commonly studied aspect and consequently it is also relatively well recognized. Also adaptive value of site fidelity in the breeding context is quite intuitively understood. But site fidelity may be also related with other aspects of animal life, like wintering, migration, and even foraging. Behind adaptivity of those is always higher survival and/or breeding performance of individuals but different mechanisms are then involved.

Site-fidelity may be related with personality. During the incubation period (but not chick rearing), bolder individuals were more site-faithful during the foraging (Harris et al 2019).

From Harris et al 2019.

Students in a classroom

Public territories (e.g., public park, lecture hall at the university, trains, and buses) are not owned, and therefore, it is very difficult to assert control. Occupancy is usually very short, control is very difficult to assert, and personalizations or markings and defense are limited. Nevertheless, a repeatedly used public space, people tend to occupy the same position. The results of Costa (2012) showed very low mean displacements of students both in halls and classrooms.

Literature

Costa, M. (2012). Territorial Behavior in Public Settings. Environment and Behavior, 44(5), 713–721. https://doi.org/10.1177/0013916511403803

Greenwood, P. J. (1980). Mating systems, philopatry and dispersal in birds and mammals. Animal Behaviour, 28(4), 1140–1162. https://doi.org/10.1016/S0003-3472(80)80103-5

Harris, S. M., Descamps, S., Sneddon, L. U., Bertrand, P., Chastel, O., & Patrick, S. C. (2020). Personality predicts foraging site fidelity and trip repeatability in a marine predator. Journal of Animal Ecology, 89(1), 68–79. https://doi.org/10.1111/1365-2656.13106

Kwon, E., Valcu, M., Cragnolini, M., Bulla, M., Lyon, B., & Kempenaers, B. (2022). Breeding site fidelity is lower in polygamous shorebirds and male-biased in monogamous species. Behavioral Ecology, 33(3), 592–605. https://doi.org/10.1093/beheco/arac014

Merkle, J. A., Abrahms, B., Armstrong, J. B., Sawyer, H., Costa, D. P., & Chalfoun, A. D. (2022). Site fidelity as a maladaptive behavior in the Anthropocene. Frontiers in Ecology and the Environment, 20(3), 187–194. https://doi.org/10.1002/fee.2456

Perrin, C., & Goudet, J. (2001). Dispersal. In J. Clobert, E. Danchin, Dhond AA, & N. JD (Eds.), Dispersal (pp. 123–142). Oxford Univerity Press.

Székely, T., Thomas, G. H., & Cuthill, I. C. (2006). Sexual conflict, ecology, and breeding systems in shorebirds. BioScience, 56(10), 801–808. https://doi.org/10.1641/0006-3568(2006)56[801:SCEABS]2.0.CO;2

Switzer, P. V. (1993). Site fidelity in predictable and unpredictable habitats. Evolutionary Ecology, 7(6), 533–555. https://doi.org/10.1007/BF01237820

Trochet, A., Courtois, E. A., Stevens, V. M., Baguette, M., Chaine, A., Schmeller, D. S., & Clobert, J. (2016). Evolution of sex-biased dispersal. Quarterly Review of Biology, 91(3), 297–320. https://doi.org/10.1086/688097