| dc.description.abstract | ABSTRACT
This study is focused on the comparative analysis of variables related to the trophic
niche plasticity in the Galapagos sea lion (Zalophus wollebaeki) and the Galapagos
fur seal (Arctocephalus galapagoensis), which are endemic species of this
Archipelago. There is a great concern regarding the future of these otariids
because of their high trophic vulnerability so that the study not only the diet but
also the way these animals obtain their food will be useful to understand and
predict their survival possibilities in the long term. There exist several techniques to
determine the trophic ecology in pinnipeds as: 1) scats analysis, 2) Stable isotopes
(δ13C y δ15N) and 3) Satellite telemetry; that complement each other to determine
foraging habits, with the aim of obtaining higher resolution. The objectives of this
study are: A) To know the foraging habits of Z. wollebaeki and its space-time
variation, B) To establish if there exist differences in terms of foraging strategies,
between Z. wollebaeki and A. galapagoensis from rookeries where they coexist.
The scat analysis (n=330) in Z. wollebaeki gave as a result space-time changes in
the foraging spectrum composition and also an intra-population diversification in
diet during the 2006 and 2009 breeding seasons, while its trophic breadth
corresponded to a specialist predator (Levin = 0.07). A differential behavior was
observed in Z. wollebaeki foraging trips (n=10), a result that was given by different
diving behavior patterns (epipelagic and benthic). In spatial terms, isotopic values
(n=321) showed differences regarding foraging grounds (δ13C: Kruskal-Wallis test,
p=0.015); however an equilibrium was maintained in relation to the trophic level of
their diet (δ15N: Kruskal-Wallis test, p=0. 152). δ13C and δ15N for both species
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(n=91) were associated to differences in foraging grounds and trophic level (t-test,
p≤0.001 and p=0.001 respectively), where Z. wollebaeki showed a coastal
strategy, focused on the consumption of small epipelagic fishes, in contrast to A.
galapagoensis that turned out to be a more oceanic predator, feeding on small size
squids. These results were consistent with the location of animals at sea; geopositioned
registers indicated that these species were found in the environments
previously mentioned. The results of this study showed a relevant finding in a
scenario where species that manage to survive in a highly demanding ecosystem
in terms of availability of resources, have developed a high degree of plasticity in
their foraging habits that allows them to facilitate their survival. | |
