Conversely, when food is extremely abundant, an aggressive individual excluding others from a food source may waste energy that could be allocated to more profitable activities, such as feeding or resting, and may expose itself to higher predation risks (Carpenter 1987 Martel 1996 Diaz-Uriarte 1999 Kim et al. When food abundance is low, the area needed to secure enough food may be too large to efficiently expel competitors, increasing the costs of defense for an aggressive individual. Resource defense behaviors, such as territoriality and temporary defense of food patches, are often explained by the spatial and temporal distribution of food resources (Brown 1964 Grant 1993). Our results show the importance of accounting for variation in space use among individuals as it translated into varying levels of defense and monopolization of feeders regardless of food resource distribution. Our study is among the first to quantify the joint use of food resource by overlapping individuals unconstrained in their use of space. The reverse effect of visibility in open habitats was more difficult to interpret as it was probably confounded by perch availability, from which a bird can defend its feeder. Defense was enhanced by visibility near feeders, but only in forested habitats. Although the apparent capacity to defend feeders was not affected by competition or nectar sucrose concentration, the level of monopolization decreased with increasing number of competitors and higher nectar quality. The level of spatial concentration at feeders and its negative effect on NVC was, however, highly variable among individuals, suggesting a continuum in resource defense strategies. Individuals who were more concentrated at certain feeders on a given day and who were more stable in their use of the grid throughout the season gained higher exclusivity in the use of those feeders on that day, especially for males competing against males. We modeled the number of visits by competitors (NVC) at feeders in response to space use by a focal individual potentially defending a feeder, number of competitors, nectar sucrose concentration, and habitat visibility. Our study system consisted of a 44 ha systematic grid of 45 feeders equipped with PIT tag detectors recording every visit made at feeders. Here, we addressed defense and monopolization of nectar feeders in a population of free-ranging ruby-throated hummingbirds marked with passive integrated transponder (PIT tags). Yet, studies frequently focus on one or two factors, overlooking the complexity found in natural settings. However, factors such as competition, habitat complexity, and individual space use may also affect the capacity of individuals to defend and monopolize resources. Resource defense behavior is often explained by the spatial and temporal distribution of resources.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |