Trophic ecology

Trophic ecology is the discipline that studies the flows of matter and energy in ecosystems, which determines the distribution and presence of different organisms and their function. In the case of animals, they can be consumers, predators or decomposers, and therefore have a position and specific function in food webs. They Animals consume trophic resources according to their availability in the environment and their energy contribution. They consume trophic resources according to their availability in the environment and the energy provided. In addition, differences in diet can also condition the vital parameters of individuals, such as productivity and survival and, ultimately, the dynamics of the population. The study of the diet of a species allows to know its role in the food web of a community and its requirements to develop its vital cycle. Besides, changes in the diet of a species over time or space may inform on the abundance and availability of trophic resources.

In the case of raptors, the most common methods for determining their diet are based on the analysis of prey remains and pellets (the small balls that raptors regurgitate through their beaks that contain indigestible parts of eaten animals) or direct observation of prey delivered to nestlings. Apart from these conventional methods, several studies in Ecology have shown that the proportion of certain stable isotope (C, N and S) in a predator reflects its diet, as this proportion is transmitted from one level to another in the food chain in a predictable manner. Stable Isotope Analysis (SIA), that requires feather samples taken from chicks during the breeding season, may provide diet estimates from the sampled individuals when several chicks are raised in the same nest, contrary to pellet analysis, and open a range of possibilities within the field of trophic ecology. However, SIA still present some disadvantages, such as it generates data about assimilated rather than ingested prey and do not distinguish individual prey species in predators’ diet, unlike pellet analysis, which provides information on the ingested prey rather than assimilated. For these reasons, we use both methods (pellet and SIA) for determining the diet of species such as the Bonelli’s eagle or the Egyptian vulture and, thus, for diagnosing environmental conditions in territories and populations, as well as changes over time.