Territorialidad y relaciones espaciales en rapaces diurnas. Patrones y procesos a escala global y local

Abstract

Understanding and predicting the spatio-temporal dynamics of animal populations remains a challenge and one of the main aims in Ecology. In this context, the study of territoriality can provide valuable information on the population dynamics, density and spatial organization. Raptors have often been used as models to study territorial behavior and its ecological implications. However, certain aspects remain poorly explored, such as the factors that promote this behavior at global scale, the influence of this behavior on other characteristics of raptors such as the reverse size dimorphism (RSD), or how territoriality and the interactions with other species affect the spatial organization of their populations. The aim of this thesis is to deepen the knowledge of both territoriality and spatial relationships in diurnal raptors, addressing four key aspects: 1) the determinants of territorial behavior, 2) territoriality as a determinant of other characteristic traits in raptors (RSD), 3) territoriality of predators as an indicator of the ability of ecosystems to support wildlife populations, and 4) the interspecific spatial relationships as indicators of interactions between species of a raptor guild. The first chapter of the thesis (chapter 1) presents a general introduction to territorial behavior, and the factors associated with this behavior and the spatial organization of raptors. The first section (chapters 2 and 3) of this dissertation is focused on general patterns associated with territorial behavior of diurnal raptors, through comparative analyses between species of the Western Palearctic and the New World, and taking into account their phylogenetic relationships. Chapter 2 analyzes main prey type, nesting site type, average prey size and average body size as determinants of territorial behavior and territory size of 74 raptor species. Territorial behavior was associated with most agile prey and structurally complex nesting sites, probably because of the difficulty to hunt agile prey, and because of the protection or inaccessibility conferred by complex nesting sites upon predators. Within the territorial species, those hunting the most agile and largest prey had larger territories, probably because these prey are less available than most vulnerable, or than smaller and more numerous, prey. In Chapter 3 we examine the relationship of territorial behavior, territory size, agility of the main prey and hunting habitat complexity with the degree of RSD in 75 species of raptors. The most important factor was the prey agility, followed by hunting habitat, and finally the variables associated with territoriality. This is the first study that suggests hunting habitat complexity increases the RSD in raptors. Territorial species and species with the largest territories also showed the highest degree of dimorphism. However, part of the RSD variation explained by these two variables overlapped with the variation explained by the agility of the main prey; therefore, further research is needed for understanding the importance of territoriality in the evolution and maintenance of RSD in diurnal raptors. The second section (chapters 4 and 5) is focused on intra and interspecific spatial relationships of a guild of forest raptors comprised by Northern goshawk (Accipiter gentilis), Eurasian sparrowhawk (A. nisus) and common buzzard (Buteo buteo) in eucalyptus woods (Eucalyptus globulus) on the northwestern part of the Iberian Peninsula. In chapter 4 we estimate the intra-specific nests distances among the three species of raptors, taking into account habitat preferences, and compared them with other Palearctic populations, in order to evaluate the ability of this novel forest ecosystem to support a community of predators. The distances found were similar and, for some species, even shorter than those reported in the literature. These results suggest that the study area, including the forest and the surrounding nonforest areas, provides a similarly good or even better nesting habitat for these predators than other ecosystems. All three species nested preferably in stands of eucalyptus that were mixed with native species, with high structural complexity and large trees. In chapter 5 we study the spatial organization of the raptor guild and its relationship with the interspecific interactions, taking into account the territoriality of the species and their habitat preferences. The guild of top-predators studied presented a very organized and hierarchical spatial distribution with a dominant predator (goshawk) and a subordinate one (sparrowhawk), and within the guild, both negative (super-predation) and positive (commensalism and possible mutualism) relationships were established. The mechanisms that promoted the coexistence of these predators were the different phenology of species, the spacing from the dominant predator, the spatial refuges, the low interspecific synchrony between neighboring territories, and the segregation of the predator’s diets. In the general discussion (chapter 6) we contrast the main results of the different chapters of this PhD Thesis. First, we discuss the general patterns of the determinants of territoriality and RSD in diurnal raptors. Then, we discuss the intra and interspecific spatial relationships of a forest raptor guild studied at local scale. Lastly, we summarize the main factors influencing the nest position of raptors and, therefore, their spatial organization. And finally, in Chapter 7 we present the general conclusions of this PhD Thesis.