Yáber, María Carolina. Ph.D., Purdue University, December, 2000. Sociality and Dispersal in Tropical Wrens: Implications of Conservation. Major Professor: Dr. Kerry N. Rabenold.
Understanding the interaction between intrinsic constraint, environmental barriers, and selective pressures favoring dispersal in essential to predicting the effects of habitat fragmentation on population stability, especially in rapidly changing tropical environments where the dispersal decision can be complicated by social systems.
Stripe-backed wrens (Campylorhynchus nuchalis) are cooperatively breeding birds in the South America savanna, in which young individuals delay breeding and natal dispersal, and effectively aid in rearing young. Five marked populations with study histories of 6-21 years make it possible to: 1) determine how sociality influences the pattern of intra- and inter- population dispersal for females and males, and 2) evaluate how dispersal between populations influences the viability of populations of social species in patchy environments.
Dispersal in stripe-backed wrens is viscous and female-biased; reproductive success of female dispersers is higher than for male dispersers, and short-distance dispersal is favored by an advantage of proximity in competition, particularly in productive large groups. Males have similar fitness (measured as the mean number of juvenile fist-order relatives produced annually) whether they breed in another group or help in their natal territory. Males that disperse have lower reproductive success than females because they are mainly limited to breeding in pairs. Females, in contrast, gain breeding positions almost exclusively through dispersal. Male and female between-population dispersers had similarly low reproductive success, and such long- distance dispersal is less common and selective, resulting in a very low level or effective inter- population dispersal. Population dynamics are variable and likely independent among populations, as are variations in demographic variables. Survival, reproduction and dispersal appear not be density-dependent, although breeding females in two populations at low densities consisted mainly of immigrants from other populations.
These results support a “metapopulation” paradigm, in which viability of each population is likely to be linked to the others by dispersal. The potential exists for “rescue” of declining populations by dispersal from others with higher productivity at that time. In spite of social constraints on dispersal, and the handicap of small effective population size imposed by sociality, sets of interacting populations in fragmented landscapes may be less extinction-prone than similar isolated populations.