James A. Rice

Prey selection naticid gastropods; experimental tests and application to the fossil record

Because predation by drilling gastropods is uniquely preservable in the fossil record, it represents important evidence for the study of coevolution. Previous studies of drilling gastropod predation have been largely descriptive and sometimes contradictory. We formulate and test a model of prey selection by naticid drilling gastropods. The model adequately predicts both prey species selection and prey size selection. Prey preferences parallel prey profitabilities, determined by calculating prey species-specific and predator size-specific cost-benefit functions. The model also specifically suggests the evolution of potential refugia from predation and the evolution of potential predatory attributes. Application of the model to several Miocene and Pliocene assemblages studied by Thomas (1976) corroborates the feasibility and utility of this approach in examining the evolutionary record of naticid predation, which extends from the Late Mesozoic. Apparent evolutionary stasis and convergent morphological trends among prey species may be consistent with continuous selection pressures against predation.

Independent Evaluation of A Bioenergetics Model For Largemouth Bass

We evaluated a bioenergetics model for largemouth bass, Micropterus salmoides, using independent field data on temperature, feeding, and growth of bass in Lake Rebecca, Minnesota. Model predictions of body mass based on observed temperatures and daily ration estimates fell within 2 SE of observed mean body masses on seven of nine sampling dates over a 4—mo period. We employed three statistical methods to evaluate the fit between predicted and observed growth. A lack—of—fit test detected no significant lack of fit between simulated and observed body masses; partitioning mean squared error showed that 76% of the variance was due to random variation rather than to systematic errors, and a reliability index indicated agreement between predicted and observed masses within a factor of 1.12. Growth simulations were relatively robust with respect to simulated errors in the input variables temperatures and swimming speed, but were sensitive to errors in initial body mass. The model used to observed growth to predict cumulative food consumption over the sampling season; the prediction was within 8.5% of an extrapolation from field data. Estimation of consumption rate as a constant proportion of maximum ration for the whole season was shown to be inappropriate; however, three intervals that used different constant proportions of maximum ration fit the data and corresponded to observed changes in bass diet.

Evaluating the constraints of temperature, activity and consumption on growth of largemouth bass

SynopsisWe present a bioenergetics model for largemouth bass (Micropterus salmoides) which simulates growth as a function of body size, temperature, activity and consumption level. We apply the model to investigate seasonal changes in condition factor exhibited by bass in Par Pond, South Carolina, a reservoir receiving heated effluent. Previous authors have suggested that these changes occur due to bioenergetic constraints, primarily the effects of heated effluent on metabolic rate. Model simulations were used to evaluate the hypotheses that seasonal changes in condition factor were caused by the heated effluent, seasonally variable activity, seasonally variable consumption, or reproductive costs.Results indicate that temperature is not directly responsible for the seasonal changes in condition factor. Bass moderate the influence of the heated effluent via behavioral thermoregulation. Activity is not a major factor, and spawning weight-loss can account for only a small portion of the observed variation. However, the pattern of seasonal changes in body condition may be adequately explained by seasonal variations in consumption. The patterns of consumption rate and/or prey availability suggested by model simulations represent testable hypotheses.

Exploration of Mechanisms Regulating Larval Survival in Lake Michigan Bloater: A Recruitment Analysis Based on Characteristics of Individual Larvae

Abstract Estimates of relative egg deposition and larval abundance suggest that events occurring between spawning and the first 1–2 months after hatching play a major role in determining recruitment success of bloater Coregonus hoyi in Lake Michigan. Although relative egg deposition in 1983 was only 57% of that in 1982, larval recruitment was 2.4 times greater in 1983. We investigated mechanisms governing survival of larval bloaters by comparing characteristics of individual “survivors” through the first 1–2 months of life with those of larvae at earlier life history stages. Otolith analysis was used to identify stress periods and to determine ages, first-feeding dates (close correlates of birthdate), and average growth rates of individual bloater larvae from hatching to nearly 2 months of age in 1982 and 1983. Differences between the observed distribution of first-feeding dates for newly hatched larvae and the expected distribution predicted from egg deposition showed that eggs spawned early experienced ...

Interactions between Size-Structured Predator and Prey Populations: Experimental Test and Model Comparison

Abstract Because predation mortality is often size-dependent, the survival and size structure of prey populations may vary substantially depending on the size structure of the predator assemblage. We tested this hypothesis in a replicated pond experiment in which a bimodal size distribution of young-of-year spot Leiostomus xanthurus was exposed to two sizes of southern flounder Paralichthvs lethostigina, each predator size-group present alone or together, at densities providing equal predation pressure, After 3 weeks, we examined cohort survival and size distributions of remaining spot. In the no-predator controls, spot size-frequency distributions were essentially unchanged, and survival of the large- and small-spot cohorts was similar. However, the size distribution of survivors, and the relative survival of large- and small-spot cohorts, differed markedly with the size structure of the predator assemblage, In the presence of small southern flounders, the large-spot cohort survived 4 times better than t...

Evaluating Otolith Analysis for Bloater Coregonus hoyi: Do Otoliths Ring True?

Abstract Laboratory experiments with known-age bloater larvae raised under constant photoperiod (12 h light: 12 h darkness) showed that deposition of otolith rings began at first feeding and occurred daily at all but the lowest growth rates. Based on ring counts, the age of individual bloaters could be estimated within ±6 d over the first 5 months of life. Otoliths of larvae fed high rations interrupted by 5-d periods of starvation or low rations contained obvious bands of abnormally low-contrast rings corresponding to these stress periods. The relationship between fish length and otolith diameter varied among experiments, independent of growth rate. Therefore, back-calculation of length at age will require an estimate of this relationship for each field application.

Predation on juvenile fishes: dynamic interactions between size-structured predators and prey

Predation is a major source of mortality for most larval and juvenile fishes (Houde, 1987; Bailey and Houde, 1989). The magnitude and nature of this mortality can substantially affect cohort survival and size distribution, and selectively influence which individuals survive (Nielsen, 1980; Zaret, 1980; Rice et al., 1987, 1993b). These dynamics during the early life history are often important in determining the population dynamics and community structure that we observe at the adult stage (Tonn and Paszkowski, 1986; Kerfoot and Sih, 1987). A better mechanistic understanding of the predation process may help us understand and predict these consequences.

Prey patchiness and larval fish growth and survival: inferences from an individual-based model

Abstract We used an individual-based simulation model to evaluate how prey patchiness and fish swimming behavior affect larval fish survival and mortality source (predation or starvation). Simulations revealed that cohort survival increased linearly with greater average patch residence times and that patch residence times for individual fish with different fates (survived, starved, eaten) diverged substantially during the first few days of feeding. Further, by examining the interaction of patch spatial distribution (uniform random versus clumped) with three possible swimming behaviors, we found that swimming behavior, via its effect on prey encounter and feeding rates, affected both cohort survival rates and whether fish died from predation or starvation, but that the spatial distribution of patches (fine-scale (100s m)) only influenced whether fish died from predation or starvation. Within a particular patch spatial arrangement, however, patch intensity (division of food between patches and non-patches) had a major effect on survival. Except at high food levels, fish did not survive when there were no patches, suggesting that average, well-mixed prey densities will not support sufficiently rapid growth for survival. As patch intensity increased, survival increased to a maximum and then declined, with peak survival occurring at higher patch intensity as average food concentration declined. Finally, the degree of patchiness also determined the intensity of selection on growth rates. In patchier environments, there was stronger selection for fast growth rates leading to eight-fold differences in average cohort growth rates after only three days of growth. In general, survival was not directly related to fast cohort growth the best survival occurred with high average prey densities and weak patchiness. Prey patchiness, by influencing the average as well as the variance in individual growth rates, can have a substantial impact on survival rates of larval fish cohorts.

Size-Dependent Effects of Continuous and Intermittent Feeding on Starvation Time and Mass Loss in Starving Yellow Perch Larvae and Juveniles

Abstract Starvation rates of fish larvae living in patchy prey environments can have an important impact on cohort survival and recruitment. Despite this, little is known about how fluctuations in feeding experience influence starvation resistance and how this changes with ontogeny. Fish previously exposed to fluctuating food densities may not respond to long periods without food in the same way as fish previously exposed to a constant prey density. In a series of laboratory experiments with larvae and juveniles of yellow perch Perca flavescens, we tested the effects of continuous and intermittent feeding on times to starvation and on mass loss up to death from starvation for fish with initial total lengths of 10, 15, and 20 mm. Results indicated that proportional mass loss up to starvation was independent of fish mass, but that it did depend on feeding history. Fish that fed continuously before starvation all died after losing the same proportion of body mass (55%), but intermittent feeders died when the...

Predation at a snail's pace: what's time to a gastropod?

SummaryPredation by naticid gastropods shows evidence of adaptation to maximize the rate of energy intake. The predation rate of Polinices duplicatus feeding on artificially altered, thin-shelled Mercenaria mercenaria was faster than the predation rate on normal Mercenaria. The rate of energy intake was limited by handling time. The time saved by predation on thin-shelled prey was used to forage. Thus time was shown to be valuable to P. duplicatus, and cost-benefit functions using time and energy as currencies are appropriate for estimating dietary efficiency and predicting prey choice.Despite the clear superiority of thin-shelled prey, P. duplicatus did not learn to prefer this novel prey type, suggesting that predator choices are sterotyped, reflecting optima selected over evolutionary time.