Same size – same niche? Foraging niche separation between sympatric juvenile Galapagos sea lions and adult Galapagos fur seals

Abstract

Summary 1.In vertebrates, patterns of resource utilization change throughout development according to age-and or size-specific abilities and requirements. Thus, interspecific competition affects different age classes differently. 2. Adults of sympatric species often show distinct foraging niche segregation, but juvenile resource use might overlap with adult competitors of similar body size. Resultant negative effects on juveniles can have important consequences for population dynamics, yet such interactions have received little attention in studies of mammalian communities. 3. Using GPS tracking devices, time-depth recorders and stable isotope data, we compared diving depth, activity time, trophic position and foraging habitat characteristics to investigate foraging niche overlap between similar-sized sympatric juvenile Galapagos sea lions (Zalophus wollebaeki) and adult Galapagos fur seals (Arctocephalus galapagoensis) and compared each group with much larger-bodied adult Galapagos sea lions. 4. We found little indication for direct competition but a complex pattern of foraging niche segregation: juvenile sea lions and adult fur seals dived to shallow depths at night, but foraged in different habitats with limited spatial overlap. Conversely, juvenile and adult sea lions employed different foraging patterns, but their foraging areas overlapped almost completely. 5. Consistency of foraging habitat characteristics between juvenile and adult sea lions suggests that avoidance of competition may be important in shaping foraging habitat utilization. Resultant specialization on a limited habitat could contribute to low sea lion numbers that contrast with high fur seal abundance. Our data suggest that exploitation by multiple predators within spatially restricted foraging ranges of juveniles might negatively impact juvenile foraging success and ultimately influence population dynamics.

Navigating uncertain waters: a critical review of inferring foraging behaviour from location and dive data in pinnipeds

“…2.1a).Device must be in line-of-sight range of base station(s) and/or mobile receiver(s) to record locations. Signal can be interrupted by terrain.[31, 32, 36, 37, 184]GPS Logger (Fig. 2.1a)Sirtrack F1GFastloc ® GPSArchivalMainly individuals with restricted ranges (e.g.…”

“…Study limited to specific timescales (e.g. pre-moult/breeding season).[36, 37, 185]Argos relay tags (Fig. 2.1c)SMRU 9000x SRDL; Wildlife Computers Mk10 SPLASH Tag; Sirtrack KiwiSat 101; Telonics ST-10 PTTArgosArgosVery widely used.…”

“…Archival TDRs and positional loggers (collecting high-resolution Global Positioning System (GPS)-derived location data) are used widely today, but studies are limited to life stages and/or species in which individuals are easily re-encountered and re-captured. For example, many studies use archival devices to track the movements and dive behaviour of lactating otariids (eared seals) [33, 36, 37]. Unlike many phocid (true seal) species, otariid pups have a protracted dependency period, during which they remain on the colony whilst the mother makes repeated foraging trips offshore.…”

Different space preferences and within-host competition promote niche partitioning between symbiotic feather mite species

“…Published by Elsevier Ltd. All rights reserved. and interspecific interactions (Holmes, 1973;Sousa, 1994;Pulliam, 2000;Nicholls and Racey, 2006;Jeglinski et al, 2013). However, within-host symbiont distributions, and the way these vary in relation to host characteristics, changes in species' abundance, or symbiont co-occurrence among individual hosts, are poorly known for most host-symbiont systems (Choe and Kim, 1988).…”

Lazy sons, self-sufficient daughters: are sons more demanding?

“…Furthermore, the significant negative correlation between the time yearlings spent diving while at sea and their trophic position (d 15 N values) relative to their mothers (Fig. 3) indicates that yearlings obtain food when actively diving at sea (see also Jeglinski et al, 2012;Jeglinski, Goetz, Werner, Costa, & Trillmich, 2013). Using stable isotope analyses, Jeglinski et al (2012) showed that yearlings feed at a lower trophic level than pups, indicating that they are no longer entirely dependent on maternal input (which leads to the highest enrichment of d 15 N in skin tissue).…”