Individual Variation in the Timing of Ontogenetic Niche Shifts in Largemouth Bass

Abstract

The transition to piscivory is a crucial ontogenetic niche shift for many primarily piscivorous fishes. An early transition to piscivory may increase growth, decrease mortality, and therefore enhance lifetime fitness. Although much is known about the extent and causes of variation in the timing of the shift to piscivory among species and among cohorts within a species, little is known about the extent and causes of variation in the timing of the switch to piscivory among individuals within a single cohort. Here, I link otolith age and growth analysis to direct diet and stable isotope analyses to examine variation in the timing of the transition to piscivory and its causes among individual members of the 1994 largemouth bass cohort in Paul Lake, Michigan. Stable isotope and direct diet analyses indicate that only a few members of the 1994 cohort were able to shift to and sustain piscivory in their first summer of life (early piscivores), while most cohort members would have to wait until their second summer of life to become piscivorous (late piscivores). Significant differences in growth rate between early and late piscivores emerged shortly after 18 June, the first date of possible piscivory by early piscivores, after which early piscivores began to grow at rates nearly twice that of late piscivores. Otolith and stable isotope analyses combined indicate that an early hatching date was necessary, but not sufficient, to explain variation in the timing of the transition to piscivory. All early piscivores were hatched early in the summer, but many early-hatched members of the 1994 cohort did not shift to piscivory in their first summer of life. A combination of at least 10 days of variation in hatching dates and higher-than-average growth rates was required for early piscivores to switch to and sustain piscivory in their first summer of life. Individuals that were able to make the early transition to piscivory most likely benefited from both increased survival and fecundity over much of their life, the combination of which would confer a substantial fitness advantage upon individuals able to make the early transition to piscivory.

Feeding Ecology of Juvenile Yellowfin Tuna from Waters Southwest of Taiwan Inferred from Stomach Contents and Stable Isotope Analysis

“…The ontogenetic stages of a fish involve physical, structural, and physiological changes that result in behavioral changes (Noakes and Godin 1988). The time when fish shift to piscivory varies among individuals for the same cohort (Post 2003). Early hatched individuals with higher growth rates can make an (4) 4.2 (1.0) ¡17.87 (1.1) Amphipoda (5) 7.4 (2.1) ¡19.7 (1.6) Crab megalopa (3) 5.1 (0.3) ¡19.7 (1.2)…”

“…Stable isotope analysis can provide further information to that obtained from the analyses of stomach contents (Pauly et al 1998;Pinnegar et al 2003) and can be used to determine diet or niche shifts (Grey 2001;Post 2003;Hammerschlag-Peyer et al 2011) or to acquire accurate data regarding feeding habits (Harvey et al 2002). Stable isotope analyses are based on measurements of the carbon and nitrogen isotope compositions of an organism's tissues, which contain information about the food or nutrient sources of the organisms consumed.…”

Largemouth bass consumption demand on hatchery rainbow trout in two Washington lakes

“…Greater open water habitat could have encouraged crayfish populations and increased their exposure to largemouth bass predation in South Twin Lake. However, in North Twin Lake, small largemouth bass were much more piscivorous, suggesting a greater encounter frequency, capture success rate and/or abundance of smaller golden shiner (Savino and Stein 1982, 1989, Post 2003. The proportion of medium and large largemouth bass was much greater in North Twin Lake, suggesting an earlier onset to piscivory or greater survival rates (Post 2003).…”

“…The proportion of medium and large largemouth bass was much greater in North Twin Lake, suggesting an earlier onset to piscivory or greater survival rates (Post 2003). Earlier onset to piscivory, coupled with macrophyte architecture and distribution, may be critical to population structuring of larger largemouth bass (Bettoli et al 1992, Dibble and Harrel 1997, Garcia-Berthou 2002, Post 2003.…”

“…However, in North Twin Lake, small largemouth bass were much more piscivorous, suggesting a greater encounter frequency, capture success rate and/or abundance of smaller golden shiner (Savino and Stein 1982, 1989, Post 2003. The proportion of medium and large largemouth bass was much greater in North Twin Lake, suggesting an earlier onset to piscivory or greater survival rates (Post 2003). Earlier onset to piscivory, coupled with macrophyte architecture and distribution, may be critical to population structuring of larger largemouth bass (Bettoli et al 1992, Dibble and Harrel 1997, Garcia-Berthou 2002, Post 2003.…”