Bite Force in Four Pinniped Species from the West Coast of Baja California,Mexico, in Relation to Diet,Feeding Strategy,and Niche Differentiation

Behavioral foraging differences are known to aid in food resource partitioning in pinniped communities, but it is not known whether skull biomechanical efficiency also contributes to dietary niche partitioning. We tested this hypothesis in a community of four sympatric species of pinnipeds that co-occur along the coast of Baja California: California sea lion (Zalophus californianus), northern elephant seal (Mirounga angustirostris), harbor seal (Phoca vitulina), and Guadalupe fur seal (Arctocephalus townsendi). We tested whether their preferred prey items differed in resistivity to puncture and whether those differences were linked to the mass of the muscles of mastication and the biomechanical efficiency with which they can puncture prey items. For each prey species, we measure resistivity to puncture using texture profile analysis. We found that M. angustirostris consumes the most resistant prey and that A. townsendi consumes the least resistant. We estimated physiological cross-sectional area of the muscles of mastication for each pinniped and found that the same pair of species respectively has the largest and smallest theoretical value of muscular force. Finally, we estimated the bite force that each pinniped species requires to puncture its prey by solving Euler-Lagrange equations based on biomechanical lever model parameters measured from 3D digital models of the skulls. We also found differences in efficiency between the species. These data allowed us to classify the three ecomorphological types. Type 1 features a hydrodynamic skull with relatively low mandibular forces, characteristic of pelagic carnivore feeders such as A. townsendi. Type 2, represented by Z. californianus and M. angustirostris (both opportunistic feeders), is characterized by broad insertion areas for the mandibular muscles and strong teeth, permitting these predators to vary the prey target species as a function of prey availability. Type 3 features a less robust skull and a lower muscle efficiency, characteristic of benthic feeders such as P. vitulina. This evidence indicates that biomechanical differences between the species contribute to dietary niche construction.

     

Feeding habits and trophic morphology of inshore lizardfish (Synodus foetens) on the central continental shelf off Veracruz, Gulf of Mexico

The inshore lizardfish, Synodus foetens, is one of the most common coastal demersal predators on the continental shelf of the Gulf of Mexico (GOM), but the biology and feeding ecology of this species is virtually unknown. Between November 2001 and January 2003 (10 collections), 603 individuals of S. foetens ranging from 112 to 420 mm standard length (SL) and 13 to 630 g (wet weight) were collected from the continental shelf of Alvarado, Veracruz, Mexico. About 60% of the individuals had empty stomachs with the stomach fullness of the remaining individuals being distributed as follows: 5% full (24.8%), 50–75% full (13.5%), and completely full (1.7%). The mean (± SD) wet weight of stomach contents was 12.1 ± 10.8 g during the rainy season, and 19.0 ± 13.0 g during the nortes season. Seventeen prey items were identified, with the majority thereof being fish. The most important prey items were Upeneus parvus, Loligo pealei, Engyophrys senta, Trachurus lathami, and Anchoa hepsetus. Seasonal changes in the diet were observed, with U. parvus and L. pealei being the most important prey during the nortes season, whereas E. senta and L. pealei were the main items during the rainy season. Prey size selection was evident among size classes of S. foetens, although no trophic overlap was observed among size classes (C_ik ≤ 0.004). High trophic level values were determined for all size classes by season (rainy season = 4.67, nortes season = 4.84), and indicated this species belongs to the piscivorous trophic guild that preys upon both demersal and pelagic species.     

Ecological niche models reveal the potential zones of invasion of the cobia (Rachycentron canadum) in the Eastern Pacific Ocean

Hydrobiologia - Cobias (Rachycentron canadum) are large fish that live in all the tropical oceans of the world, except for the Eastern Pacific Ocean (EPO). During 2015, a cobia cage culture was...     

The carrying capacity of ecosystems

We analyse the concept of carrying capacity (CC), from populations to the biosphere, and offer a definition suitable for any level. For communities and ecosystems, the CC evokes density‐dependence assumptions analogous to those of population dynamics. At the biosphere level, human CC is uncertain and dynamic, leading to apprehensive rather than practical conclusions. The term CC is widely used among ecological disciplines but remains vague and elusive. We propose the following definition: the CC is ‘the limit of growth or development of each and all hierarchical levels of biological integration, beginning with the population, and shaped by processes and interdependent relationships between finite resources and the consumers of those resources’. The restrictions of the concept relate to the hierarchical approach. Emergent properties arise at each level, and environmental heterogeneity restrains the measurement and application of the CC. Because the CC entails a myriad of interrelated, ever‐changing biotic and abiotic factors, it must not be assumed constant, if we are to derive more effective and realistic management schemes. At the ecosystem level, stability and resilience are dynamic components of the CC. Historical processes that help shape global biodiversity (e.g. continental drift, glaciations) are likely drivers of large‐scale changes in the earth's CC. Finally, world population growth and consumption of resources by humanity will necessitate modifications to the paradigm of sustainable development, and demand a clear and fundamental understanding of how CC operates across all biological levels.     

Trophic level and overlap of sea lions (Zalophus californianus) in the Gulf of California, Mexico

Stable isotope and scat analyses were used in concert to determine trophic level and dietary overlap among California sea lions from different rookeries in the Gulf of California. Isotopic analysis of the fur of sea lion pups revealed differences in δ¹⁵N and δ¹³C values among rookeries during the breeding season. Mean δ¹⁵N and δ¹³C values varied from 20.2‰ to 22.4‰ and from −15.4‰ to −14.0‰, respectively. The pattern of differences among rookeries was similar between years in most cases. Isotopic variations among rookeries were associated with differences in prey consumption. There was a significant correlation between δ¹⁵N value and trophic level, as determined by scat analysis. Joint application of isotopic and scat analyses allowed us to identify how the feeding habits of sea lions vary with location. Our results suggest the presence of spatial structure in available prey as well as the localized use of prey by sea lions across the Gulf of California.     

The Espiritu Santo Island as a critical area for conserving batoid assemblage species within the Gulf of California

Environmental Biology of Fishes - The Espiritu Santo Island (ESI) has the highest elasmobranch richness among the Gulf of California islands, exemplifying its importance for conservation. In the...