- Email: [email protected]
1980 Dispersal
Chapter 53
1980 Dispersal THE CONCEPT Young animals leave their parents’ habitat in search of unoccupied habitat, more productive habitat, or mating opportunities with unrelated animals. The age and sex of dispersing animals is predictable based on mating system and life history characteristics.
THE EXPLANATION Greenwood’s (1980) exploration of how dispersal interacts with animals’ mating systems came soon after Emlen and Oring’s (1977) exposition on mating systems. In birds and mammals, young animals may be much impacted by their parents’ continued presence and use of resources. Competition with parents is potentially a losing prospect, but dispersing is highly risky as young animals may have to traverse inhospitable terrain, be exposed to predators, and may find that the habitat where they arrive at is equally crowded. Observations leading up to Greenwood’s paper had noted that male young sometimes dispersed while females sometimes dispersed, but discovering patterns had proven difficult. Greenwood (1980) built on the accumulation of natural history knowledge, noting that female birds were more often dispersers, while in mammals it was the males that more often dispersed. Staying close to home, or philopatry, appears in his analysis to be predicted by the mating system. Mammals are more often polygynous, so that males move away from a group that includes their mother and sisters. Birds are more often monogamous, perhaps favoring female movement because the future reproduction of their father depends on retention of his territory. Dispersal is important in finding new habitat for feeding and nesting, but it comes with risks. Dispersing animals may be more exposed to predation or starvation. Game theory (see Chapter 38: 1973 Game Theory) helps to analyze situations such as this, in which animals of each sex could attempt to outwait the other. A contrary view about mammalian dispersal notes that in some mating systems (see Chapter 50: 1977 The Evolution of Mating Systems) females may find it substantially easier to join new groups than males, thus making female Conceptual Breakthroughs in Ethology and Animal Behavior. DOI: http://dx.doi.org/10.1016/B978-0-12-809265-1.00053-8 © 2017 Elsevier Inc. All rights reserved.
169
170
Conceptual Breakthroughs in Ethology and Animal Behavior
dispersal less risky. Wild horses and a variety of primates possibly exemplify this point. Dispersal is also extremely important in helping animals to obtain an appropriate level of outbreeding. Animal in populations that do not disperse at all risk becoming inbred and suffering from the effects of lost genetic variation. Under circumstances in which dispersal is limited by geography, such as island populations, the impacts of mate choice and sexual selection may be muted, as there can be a high degree of similarity among potential mates. As with finding new habitat in which to live, finding new genetic terrain is a complicated proposition. This is a difficult cost benefit analysis that takes generations of evolution to solve. Greenwood’s (1980) paper is among the most highly cited papers in the fields of animal behavior, ethology, and behavioral ecology. This is partly because of his thorough data review and insightful analysis. But not everyone agrees with his fundamental point that the male/female difference in dispersal between mammals and birds is a derivative of their mating systems. Also, the natural world is full of exceptions and more knowledge of individual species’ dispersal patterns, have not undone the generalization, but they have helped us to understand that a species’ evolutionary history can drive dispersal patterns that run counter to the grain of the generality.
IMPACT: 5 Given the importance of dispersal in animal’s lives, it is very surprising that stronger consideration had not been given, prior to Greenwood’s 1980 publication, to patterns of dispersal and the evolutionary forces that might drive male female differences in dispersal. This led to a broader consideration of contrasts between birds and mammals and to the interaction of life history characteristics with dispersal patterns.
SEE ALSO Chapter 21, 1954 Life History Phenomena; Chapter 44, 1974 Parent Offspring Conflict; Chapter 50, 1977 The Evolution of Mating Systems.
REFERENCES AND SUGGESTED READING Dobson, F.S., 2013. The enduring question of sex-biased dispersal: Paul J. Greenwood’s (1980) seminal contribution. Anim. Behav. 85, 299 304. Emlen, S.T., Oring, L.W., 1977. Ecology, sexual selection, and evolution of mating systems. Science 197, 215 223. Greenwood, P.J., 1980. Mating systems, philopatry and dispersal in birds and mammals. Anim. Behav. 28, 1140 1162. Greenwood, P.J., Harvey, P.H., 1982. The natal and breeding dispersal of birds. Ann. Rev. Ecol. Syst. 13, 1 21. Johnson, M.L., Gaines, M.S., 1990. Evolution of dispersal-theoretical-models and empirical tests using birds and mammals. Ann. Rev. Ecol. Syst. 21, 449 480.
1980 Dispersal THE CONCEPT Young animals leave their parents’ habitat in search of unoccupied habitat, more productive habitat, or mating opportunities with unrelated animals. The age and sex of dispersing animals is predictable based on mating system and life history characteristics.
THE EXPLANATION Greenwood’s (1980) exploration of how dispersal interacts with animals’ mating systems came soon after Emlen and Oring’s (1977) exposition on mating systems. In birds and mammals, young animals may be much impacted by their parents’ continued presence and use of resources. Competition with parents is potentially a losing prospect, but dispersing is highly risky as young animals may have to traverse inhospitable terrain, be exposed to predators, and may find that the habitat where they arrive at is equally crowded. Observations leading up to Greenwood’s paper had noted that male young sometimes dispersed while females sometimes dispersed, but discovering patterns had proven difficult. Greenwood (1980) built on the accumulation of natural history knowledge, noting that female birds were more often dispersers, while in mammals it was the males that more often dispersed. Staying close to home, or philopatry, appears in his analysis to be predicted by the mating system. Mammals are more often polygynous, so that males move away from a group that includes their mother and sisters. Birds are more often monogamous, perhaps favoring female movement because the future reproduction of their father depends on retention of his territory. Dispersal is important in finding new habitat for feeding and nesting, but it comes with risks. Dispersing animals may be more exposed to predation or starvation. Game theory (see Chapter 38: 1973 Game Theory) helps to analyze situations such as this, in which animals of each sex could attempt to outwait the other. A contrary view about mammalian dispersal notes that in some mating systems (see Chapter 50: 1977 The Evolution of Mating Systems) females may find it substantially easier to join new groups than males, thus making female Conceptual Breakthroughs in Ethology and Animal Behavior. DOI: http://dx.doi.org/10.1016/B978-0-12-809265-1.00053-8 © 2017 Elsevier Inc. All rights reserved.
169
170
Conceptual Breakthroughs in Ethology and Animal Behavior
dispersal less risky. Wild horses and a variety of primates possibly exemplify this point. Dispersal is also extremely important in helping animals to obtain an appropriate level of outbreeding. Animal in populations that do not disperse at all risk becoming inbred and suffering from the effects of lost genetic variation. Under circumstances in which dispersal is limited by geography, such as island populations, the impacts of mate choice and sexual selection may be muted, as there can be a high degree of similarity among potential mates. As with finding new habitat in which to live, finding new genetic terrain is a complicated proposition. This is a difficult cost benefit analysis that takes generations of evolution to solve. Greenwood’s (1980) paper is among the most highly cited papers in the fields of animal behavior, ethology, and behavioral ecology. This is partly because of his thorough data review and insightful analysis. But not everyone agrees with his fundamental point that the male/female difference in dispersal between mammals and birds is a derivative of their mating systems. Also, the natural world is full of exceptions and more knowledge of individual species’ dispersal patterns, have not undone the generalization, but they have helped us to understand that a species’ evolutionary history can drive dispersal patterns that run counter to the grain of the generality.
IMPACT: 5 Given the importance of dispersal in animal’s lives, it is very surprising that stronger consideration had not been given, prior to Greenwood’s 1980 publication, to patterns of dispersal and the evolutionary forces that might drive male female differences in dispersal. This led to a broader consideration of contrasts between birds and mammals and to the interaction of life history characteristics with dispersal patterns.
SEE ALSO Chapter 21, 1954 Life History Phenomena; Chapter 44, 1974 Parent Offspring Conflict; Chapter 50, 1977 The Evolution of Mating Systems.
REFERENCES AND SUGGESTED READING Dobson, F.S., 2013. The enduring question of sex-biased dispersal: Paul J. Greenwood’s (1980) seminal contribution. Anim. Behav. 85, 299 304. Emlen, S.T., Oring, L.W., 1977. Ecology, sexual selection, and evolution of mating systems. Science 197, 215 223. Greenwood, P.J., 1980. Mating systems, philopatry and dispersal in birds and mammals. Anim. Behav. 28, 1140 1162. Greenwood, P.J., Harvey, P.H., 1982. The natal and breeding dispersal of birds. Ann. Rev. Ecol. Syst. 13, 1 21. Johnson, M.L., Gaines, M.S., 1990. Evolution of dispersal-theoretical-models and empirical tests using birds and mammals. Ann. Rev. Ecol. Syst. 21, 449 480.