Optimal foraging and fitness in Columbian ground squirrels

Ritchie, Mark E.

doi:10.1007/bf00318534

Cited by 70 publications

(38 citation statements)

References 59 publications

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“…accounting for whether the individual deviated in favour of monocots or dicots, was not correlated between field and enclosure (r 2 = 0.04, P > 0.20). The calculated energy cost of deviating from an optimal diet by a given amount (see Ritchie, 1990) was higher on average for deviations in favour of monocots, but significant deviations (based on a comparison of the predicted and observed diet, with its variance, using a z-test; Ritchie, 1988) in either direction resulted in dramatic reductions in growth, survival, and reproduction (Ritchie, 1990). Consequently, any deviation, regardless of sign, should result in lower energy intake and fitness.…”

Section: Foraging Ability As a Traitmentioning

confidence: 94%

“…I used the absolute value of this deviation as a measure of optimal foraging ability for three reasons: (1) individuals deviated from their optimal diets in favour of monocots or dicots in equal frequency (Ritchie, 1988); (2) deviating from an optimal diet appeared to reduce fitness strongly, regardless of the direction of deviation (Ritchie, 1990); (3) the absolute value of deviation was consistent across different environments but the direction of deviation was not (see Results). Deviation from an optimal diet serves as an index of the average number of foraging mistakes made by an individual each day.…”

Section: Optimal Foraging Abilitymentioning

confidence: 98%

“…uterine environment, milk quality, etc., which might affect an offspring's neurophysiological development and ultimately its foraging performance (Willham, 1972;Hayes and Eisen, 1979;Atchley, 1984;Baker et al, 1984). In particular, optimal mothers have a greater daily energy intake (Ritchie, 1990), and might have more energy or nutrients to invest in their offspring. If more energy or nutrients are invested in offspring, their neurophysiological development might be superior.…”

Section: Genetic Component Of Foraging Behaviourmentioning

confidence: 99%

“…An individual's deviation from its optimal diet appears to be consistent over time within a year and in different foraging environments (food abundance, thermal conditions, and social environment), although individuals improve between years (Ritchie, 1988). Furthermore, individuals with larger deviations have lower rates of growth, survival, and reproduction (Ritchie, 1990). Consequently, optimal foraging ability is a repeatable character, similar to other morphological or physiological traits, e.g.…”

Section: Introductionmentioning

confidence: 98%

“…In this study, I examine the resemblance in optimal foraging ability between mothers and offspring in a population of Columbian ground squirrels (Spermophilus columbianus). In two previous studies (Ritchie, 1988(Ritchie, , 1990, I showed that an optimal diet proportion for an individual is that which maximizes its daily energy intake, given its activity time and body size. An individual's optimal foraging ability is measured by its deviation in diet proportion from its own indiv~lual optimal diet (not its diet).…”

Section: Introductionmentioning

confidence: 99%

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Inheritance of optimal foraging behaviour in Columbian ground squirrels

Ritchie

1991

Evol Ecol

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in SummaryI examined the potential inheritance of the ability of Columbian ground squirrels (Spermophilus columbianus) to select an optimal diet. I calculated the diet that would maximize daily energy intake for each of 21 adult females and their litters, using a linear programming optimization model for each individual. The absolute value of the difference between an individual's predicted optimal diet and observed diet (deviation from an optimal diet) was used as a measure of an individual's foraging ability. The foraging ability of individuals was consistent over time and in different foraging environments, so I considered foraging ability to be a potentially heritable trait.Inheritance was determined from correlations of mother and offspring foraging ability. I experimentally removed some mothers just as they weaned their offspring so that offspring could not be influenced by their mother while learning to forage, while leaving the other mothers to raise their litters normally. In both cases, offspring strongly resembled their mother in foraging ability. However, offspring with mothers absent exhibited significantly larger deviations from their optimal diet. Offspring with mothers absent appeared to imitate their mother's diet during lactation, and this tendency partially explained their greater deviation. Consequently, offspring appear to inherit the ability to forage optimally from their mother, perhaps through observational learning or imitation. There may also be a genetic basis to foraging ability, but uncontrolled maternal effects in the experiment prevent a proper test for it.

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Section: Foraging Ability As a Traitmentioning

confidence: 94%

Section: Optimal Foraging Abilitymentioning

confidence: 98%

Section: Genetic Component Of Foraging Behaviourmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Inheritance of optimal foraging behaviour in Columbian ground squirrels

Ritchie

1991

Evol Ecol

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Fitness implications of seasonal climate variation in Columbian ground squirrels

Dobson

Lane

Low

et al. 2016

Ecology and Evolution

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The influence of climate change on the fitness of wild populations is often studied in the context of the spring onset of the reproductive season. This focus is relevant for climate influences on reproductive success, but neglects other fitness‐relevant periods (e.g., autumn preparation for overwintering). We examined variation in climate variables (temperature, rainfall, snowfall, and snowpack) across the full annual cycle of Columbian ground squirrels (Urocitellus columbianus) for 21 years. We investigated seasonal climate variables that were associated with fitness variables, climate variables that exhibited directional changes across the study period, and finally observed declines in fitness (−0.03 units/year; total decline = 37%) that were associated with directional changes in climate variables. Annual fitness of adult female ground squirrels was positively associated with spring temperature (r = 0.69) and early summer rainfall (r = 0.56) and negatively associated with spring snow conditions (r = −0.44 to −0.66). Across the 21 years, spring snowmelt has become significantly delayed (r = 0.48) and summer rainfall became significantly reduced (r = −0.53). Using a standardized partial regression model, we found that directional changes in the timing of spring snowmelt and early summer rainfall (i.e., progressively drier summers) had moderate influences on annual fitness, with the latter statistically significant (ρ = −0.314 and 0.437, respectively). The summer period corresponds to prehibernation fattening of young and adult ground squirrels. Had we focused on a single point in time (viz. the onset of the breeding season), we would have underestimated the influences of climate change on our population. Rather, we obtained a comprehensive understanding of the influences of climate change on individual fitness by investigating the full lifecycle.

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Diet of a rare herbivore based on DNA metabarcoding of feces: Selection, seasonality, and survival

Goldberg

Conway

Tank

et al. 2020

Ecology and Evolution

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In herbivores, survival and reproduction are influenced by quality and quantity of forage, and hence, diet and foraging behavior are the foundation of an herbivore's life history strategy. Given the importance of diet to most herbivores, it is imperative that we know the species of plants they prefer, especially for herbivorous species that are at risk for extinction. However, it is often difficult to identify the diet of small herbivores because: (a) They are difficult to observe, (b) collecting stomach contents requires sacrificing animals, and (c) microhistology requires accurately identifying taxa from partially digested plant fragments and likely overemphasizes less‐digestible taxa. The northern Idaho ground squirrel ( Urocitellus brunneus ) is federally threatened in the United States under the Endangered Species Act. We used DNA metabarcoding techniques to identify the diet of 188 squirrels at 11 study sites from fecal samples. We identified 42 families, 126 genera, and 120 species of plants in the squirrel's diet. Our use of three gene regions was beneficial because reliance on only one gene region (e.g., only trnL ) would have caused us to miss >30% of the taxa in their diet. Northern Idaho ground squirrel diet differed between spring and summer, frequency of many plants in the diet differed from their frequency within their foraging areas (evidence of selective foraging), and several plant genera in their diet were associated with survival. Our results suggest that while these squirrels are generalists (they consume a wide variety of plant species), they are also selective and do not eat plants relative to availability. Consumption of particular genera such as Perideridia may be associated with higher overwinter survival.

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Optimal foraging and fitness in Columbian ground squirrels

Cited by 70 publications

References 59 publications

Inheritance of optimal foraging behaviour in Columbian ground squirrels

Inheritance of optimal foraging behaviour in Columbian ground squirrels

Fitness implications of seasonal climate variation in Columbian ground squirrels

Diet of a rare herbivore based on DNA metabarcoding of feces: Selection, seasonality, and survival

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