In studies of cooperative breeders, the effects of group size on survival have received considerably less attention than effects on reproduction, and many empirical studies (including our own: Creel et al. Emlen (1997) summarized changes in the focus of this research, first from testing whether nonbreeding helpers truly contribute to the successful reproduction of others, thus creating a positive correlation between group size and the reproductive success of breeders (Skutch 1935 Rowley 1957), to identifying the ecological and demographic conditions that promote nondispersal and helping behavior ( Emlen 1982), to using reproductive skew models to test predictions from inclusive fitness theory about the allocation of reproduction among group members ( Vehrencamp 1980, 1983 Keller and Reeve 1994 Magrath et al. Following Darwin’s (1859) recognition that self-sacrificial behavior presents “a special difficulty, which at first appeared to me insuperable, and actually fatal to the whole theory” of evolution by natural selection, decades of research have considered the manner in which cooperative breeding can evolve through a combination of direct fitness benefits and kin selection ( Hamilton 1963 Wilson 1975). In cooperatively breeding species, adults provide care for the offspring of others by guarding them from predation, grooming them, feeding them, and even nursing them ( Brown 1987 Koenig and Stacey 1990 Creel et al. INTRODUCTION Cooperative breeding, cooperative hunting, and the effects of group size on fitness components More broadly, the relationship of effects of group size on survival and reproduction might be predicted by considering whether cooperation yields benefits that accrue to all group members (e.g., through cooperative vigilance) or benefits that must be apportioned to individuals (e.g., through cooperative hunting). The results also weaken support for the hypothesis that wild dogs are extinction prone due to group-level Allee effects. These results suggest that cooperative breeding in wild dogs cannot be fully explained by mutual direct benefit, thus reinforcing the prior inference that kin selection plays an important role in the evolution of their cooperation.
Several tests confirmed that undetected dispersal is unlikely to have produced this pattern. Data from 366 individuals over a period of 6 years showed that the survival of adults decreased with increasing pack size, with a 25% difference between the largest and smallest packs after controlling for the effects of age, sex, social status, year of study, and pack identity. The production and survival of pups are known to increase with increasing pack size, but the effect of pack size on adult survival has not been examined previously. We tested this hypothesis by examining relationships between group size, survival, and reproduction in African wild dogs ( Lycaon pictus), cooperative hunters with highly cohesive packs within which reproduction is monopolized by the dominant male and female. The stubborn and persistent hyenas stuck around and eventually we watched as they finished any scraps that had been left behind.For cooperative breeders, we hypothesize that the effects of group size on reproduction and survival might run in opposition if the benefits of grouping cannot be shared without cost. The pack moved off, probably in pursuit of more prey, as some of them were still hungry.
WILD DOGS VS.HYENAS FULL
The full pack of wild dogs won, chasing the hyenas off, and they finished what remained of the impala, leaving only the head. The noise was unbelievably loud and aggressive. We had both species running in circles around the Land Rover, with me and my guests not knowing which way to look. This was until another five wild dogs arrived and the real battle began. The Hyenas managed to dominate and keep the kill. The battle ensued between the two species, each animal desperate for the remains of the carcass:
In a moment a second wild dog arrived and not long after that, a second hyena too. The wild dog and hyena started to fight over the kill. Next we saw a Hyena coming towards us as well. I shifted into 2 nd gear to keep up with him and he led us straight to a dead impala that was 60 percent finished. It was only a few minutes later that suddenly, 50 meters to the right of my vehicle, a wild dog ran past. Two young giraffe roam the open crests with the bare marula trees setting the scene of a crisp chill in the air as the sun rises in the morning, just before the excitement began.
0 kommentar(er)
