Gary Belovsky - Academia.edu (original) (raw)

Papers by Gary Belovsky

Hobbs (this volume) raises two issues concerning my use of Linear Programming (LP) methods to mod... more Hobbs (this volume) raises two issues concerning my use of Linear Programming (LP) methods to model optimal diet choices: the models are highly sensitive to parameter values and the digestive constraint is constructed using debatable assumptions about the kinetics of digestion. He further proposes a different formulation of the digestive constraint which fails to predict diet choices using an LP model. This leads Hobbs to claim that my use of an LP model is incorrect and should be discarded, even though it has been empirically successful.

Journal of Anthropological Archaeology, Dec 1, 1988

Population changes for hunter-gatherers are modeled on the basis of nutritional intake, which is ... more Population changes for hunter-gatherers are modeled on the basis of nutritional intake, which is determined using an optimal foraging model based upon the optimization technique of linear programming. The population model not only demonstrates how hunter-gatherer demography changes with nutrition, but also shows how their density influences food abundance in the environment which in turn affects their nutritional status. Differences in food availability in different environments can be assessed by examining the effects of diierent preexploitation maxima for food abundances. Hunter-gatherer populations are predicted by the model to display a stable limit cycle which varies in severity with the maximum food abundance in the environment, being more severe at very low and high food abundances. Observed hunter-gatherer densities, growth rates, and life expectancies are shown to be consistent with the population model's predictions for different environments. The model is also used to examine the impact huntergatherers might have on their food resources including whether or not overexploitation (extinction) occurs and how their diets change in different environments with changes in population density. Finally, the model is used to examine archaeological questions about the Paleo-Indian colonization of the New World and the effects of technological innovation by hunter-gatherers. 8 1988 AC&.~~C PMS, IK.

Ecology, Aug 1, 1981

A model of food plant selection by a generalist herbivore was developed. The model was designed t... more A model of food plant selection by a generalist herbivore was developed. The model was designed to predict the species composition of the diet of an herbivore based upon the joint probabilities of whether or not an individual of a plant species satisified two threshold values: some nutritional minimum and a size limit (both minimum and maximum), and the probability that it was encountered while foraging. The model was tested using moose (Alces alces) at Isle Royale National Park, Michigan, USA. Initially the threshold values for food selection were determined empirically from the moose's observed behavior, but these empirical values were later shown to be based upon time-energy considerations. Although the model satisifed some of the criteria of optimal foraging contingency models, it appeared that the perfect knowledge assumption was not met. Rather, moose appeared to utilize a strategy of risk aversion.

Hydrobiologia, Nov 16, 2016

We examined the grazing rate of brine shrimp from Great Salt Lake, Utah (USA) at different life s... more We examined the grazing rate of brine shrimp from Great Salt Lake, Utah (USA) at different life stages under varying water temperatures, salinities, and concentrations of two of their common phytoplankton foods: Dunaliella viridis and Coccochloris elabens. Trials for a brine shrimp life stage at a specific temperature, salinity, and food concentration occurred within 50 mL test tubes for 1 h; the difference between initial and final food concentrations represented grazing rate. General trends indicated grazing rate significantly increased with progressive life stages, increased with temperature, increased with food concentration, and decreased with salinity. Grazing rates for all life stages were greater on D. viridis compared to C. elabens. Brine shrimp life stages respond differently to environmental conditions. Specifically, while juveniles and adults varied their grazing rates in response to different food concentrations and salinities, nauplii grazing rate was not affected. Only adult grazing rates increased with increasing temperature. Differences in grazing rates under varying environmental conditions have implications for brine shrimp phenology, because brine shrimp populations in the Great Salt Lake are food limited in this highly variable environment.

Springer eBooks, 2020

Great Salt Lake (GSL) is a hypersaline terminal lake and has varied historically in salinity from... more Great Salt Lake (GSL) is a hypersaline terminal lake and has varied historically in salinity from 6 to 28%. Because the lake’s salinity is much greater than in marine environments (~3.5%), salinity is often assumed to be the driving factor for GSL benthic and pelagic food webs. Certainly, many species cannot live in a hypersaline environment (e.g., fish), and the diversity of species capable of coping with hypersaline conditions is limited. However, the GSL’s benthic and pelagic food webs are adapted to these extreme saline conditions, and their dynamics (primary and secondary production, species abundances, etc.) respond in a complex fashion to the interplay of salinity, temperature, and nutrient availability. Therefore, focusing solely on salinity is not appropriate. In this chapter, we first explore historically how GSL food webs have been reported to change and found salinity to have limited impact. We next demonstrate that in recent years (1994–2018) GSL food webs varied far less with salinity than might be expected, even though salinity varied by 8.2–17.5%, because temperatures and nutrient availability covaried with salinity and showed more impacts than salinity alone. Finally, we employ the observations on the interplay of salinity, temperature, and nutrients to project how future climatic changes in the GSL watershed will affect primary producers and consumers and impact GSL food webs. These future climatic changes will have profound effects on GSL food web dynamics.

Ecology and Evolution, Jun 4, 2019

Disturbances drive plant growth and plant community structure in many different ecosystems, inclu... more Disturbances drive plant growth and plant community structure in many different ecosystems, including highly productive tropical forests, where, for example, an increase in light underneath a treefall gap can increase plant growth and alter plant community structure (Brokaw & Grear, 1991). Beyond primary producers, higher trophic levels are influenced by disturbances as well. Herbivores in many different ecosystems respond to changes in plant communities from disturbances in a variety of ways, and their taxonomy or feeding guild may affect their responses (Lewinsohn, Novotny, & Basset, 2005). Light gaps in rainforests promote the rapid growth of new leaves which increases herbivory (Angulo-Sandoval & Aide, 2000; Spiller & Agrawal, 2003), abundances of gap-specialist plants often preferred by herbivores (Coley & Barone, 1996), and the litterfall reaching the forest floor (Lodge & McDowell, 1991). Thus, consumer effects on plants may be amplified in light gaps where both herbivores and detritivores have greater resources available when consumers are limited by food. Consumer effects on vegetation structure may be modified by other factors, such as season (highly

Behavioral Ecology, 1996

Female mate choice and the benefits of this behavior are critical aspects of Darwinian sexual sel... more Female mate choice and the benefits of this behavior are critical aspects of Darwinian sexual selection, but they are seldom documented because it is difficult to identify the male trait(s) that females may be seeking. We conducted experiments with grasshoppers (Melanoplus sanguinipes: Orthoptera, Acrididae) to examine this behavior. Males that feed more intensively and select a diet mix that permits greater food intake (food intake per body mass per time) in laboratory trials were preferentially selected by females. These better foraging males on average provide greater paternal investment (greater spermatophore mass) to the female, which increases her reproductive rate (eggs produced per body mass per time). However, paternal investment may not entirely explain female choice of better foraging males, because these males were still selected even if they had their food intake restricted or had been allowed to recently mate, which reduces spermatophore production. Furthermore, males change their mating strategy in response to female choice and the foraging abilities of surrounding males. Poorer foraging males attempt forcible copulation rather than displaying and allowing female choice. A male will facultatively switch between these strategies depending on the foraging abilities of the surrounding males. While females attempt to reject forcible copulation, forcible copulation reduces the frequency with which females successfully copulate with better foraging males. Therefore, males that are less "attractive" to females adopt alternative mating strategies to counter female choice which would exclude them from mating.

Oikos, Nov 1, 1993

We conducted experiments at the National Bison Range, Montana to compare grasshopper densities in... more We conducted experiments at the National Bison Range, Montana to compare grasshopper densities in cages with and without spiders, and inside and outside avian exclosures to examine the impacts of the most common invertebrate and vertebrate predators. Spider ...

Oecologia, Aug 14, 2018

Over the past century at the National Bison Range, temperature has increased by 0.6 °C, and annua... more Over the past century at the National Bison Range, temperature has increased by 0.6 °C, and annual precipitation has decreased by 26%, despite increases in May-June precipitation over the past 35 years. Limited experimental work to date has explored plant responses produced by the interaction of changes in both temperature and precipitation, and of the existing studies, none have focused on the endangered bunchgrass ecosystem. Using a 2-year climate change manipulation experiment, we show that bunchgrass productivity increased with supplemental growing season precipitation, while warming alone exerted no significant effect. More importantly, the ratio of June precipitation to minimum temperature, a representation of the interaction of climate variables, predicted bunchgrass productivity better than either climate variable individually. This ratio acted as a surrogate index reflecting increased evapotranspiration with rising temperatures and thus better predicting soil moisture available for plant growth. Experimental warming over the summer led to significantly lower plant species richness and biodiversity, while increased precipitation, when applied over the entire summer, counteracted some of these declines. Warming also led to greater and more rapid plant senescence over the summer, resulting in greater litter production [an increase of 47.82 ± 17.82 (± SE) percentage points] and potential fire risk. Given the simultaneous changes in precipitation and temperature predicted for the next century, multi-factor experiments are essential to understand how ecosystems will respond to future climate scenarios.

Cambridge University Press eBooks, Aug 13, 1987

American Midland Naturalist, Apr 1, 1984

... americana, and avoided (diet proportion significantly less than available) Betula-papyrifera,... more ... americana, and avoided (diet proportion significantly less than available) Betula-papyrifera, Corylus cornuta, Lonicera canadensis, Abies balsamifera, Thuja oc-cidentalis ... close to the observer (&amp;lt; 50 m), and their selection of food could be observed, beaver at Grace Creek pond ...

Perspectives in Biology and Medicine, 2000

Ecological Applications, Mar 1, 2016

Selective harvesting can cause evolutionary responses in populations via shifts in phenotypic cha... more Selective harvesting can cause evolutionary responses in populations via shifts in phenotypic characteristics, especially those affecting life history. Brine shrimp (Artemia franciscana) cysts in Great Salt Lake (GSL), Utah, USA are commercially harvested with techniques that select against floating cysts. This selective pressure could cause evolutionary changes over time. Our objectives are to (1) determine if there is a genetic basis to cyst buoyancy, (2) determine if cyst buoyancy and nauplii mortality have changed over time, and (3) to examine GSL environmental conditions over time to distinguish whether selective harvesting pressure or a trend in environmental conditions has caused changes in cyst buoyancy and nauplii mortality. Mating crosses between floating and sinking parental phenotypes with two food Accepted Article This article is protected by copyright. All rights reserved. concentrations (low and high) indicated there is a genetic basis to cyst buoyancy. Using cysts harvested from 1991-2011, we found cyst buoyancy decreased and nauplii mortality increased over time. Data on water temperature, salinity, and chlorophyll a concentration in GSL from 1994 to 2011 indicated that although water temperature has increased over time and chlorophyll a concentration has decreased over time, the selective harvesting pressure against floating cysts is a better predictor of changes in cyst buoyancy and nauplii mortality over time than trends in environmental conditions. Harvesting of GSL A. franciscana cysts is causing evolutionary changes, which has implications for the sustainable management and harvesting of these cysts. Monitoring phenotypic characteristics and life-history traits of the population should be implemented and appropriate responses taken to reduce the impacts of the selective harvesting.

Journal of Orthoptera Research, Jun 1, 2002

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Oecologia, Jul 1, 1990

Seasonal energy intake was estimated for ten populations of Columbian ground squirrels (Spermophi... more Seasonal energy intake was estimated for ten populations of Columbian ground squirrels (Spermophilus columbianus) in northwestern Montana. We calculated daily energy intake for an average ground squirrel in each population using measurements of feeding time, consumption rates of different vegetation types (monocots vs. dicots), and the proportion of monocots and dicots in the diet. These daily energy intakes were multiplied by the length of the plant growing season for each population to estimate seasonal energy intake, i.e. over the ground squirrel active season. Amicable interaction rates measured for each population varied with seasonal energy intake, but not with environmental heterogeneity, sex ratio, or the ratio of adults to juveniles. In particular, amicable interactions among adult-juvenile and juvenile-juvenile pairs increased as seasonal energy intake decreased. The proportion of females breeding as yearlings increased as seasonal energy intake increased. This suggests that "harsh" environments reduce the energy available for juvenile growth and development, leading to delayed dispersal and age at first reproduction. These responses may promote the formation of kin groups and increased amicable interactions within those groups. The length of the plant growing season may determine environmental "harshness" across elevational gradients, but at a particular elevation, "harshness" may depend on factors determining daily food intake.

Evolutionary Ecology, Sep 1, 1993

Environmental Entomology, Apr 1, 2010

An important challenge facing ecologists is to understand how climate change may affect species p... more An important challenge facing ecologists is to understand how climate change may affect species performance and species interactions. However, predicting how changes in abiotic variables associated with climate change may affect species performance also depends on the biotic context, which can mediate species responses to climatic change. We conducted a 3-yr Þeld experiment to determine how the herbivorous grasshopper Camnula pellucida (Scudder) responds to manipulations of temperature and population density. Grasshopper survival and fecundity decreased with density, indicating the importance of intraspeciÞc competition. Female fecundity tended to increase with temperature, whereas grasshopper survival exhibited a unimodal response to temperature, with highest survival at intermediate temperatures. Grasshopper performance responses to temperature also depended on density. Peak survival in the low-density treatment occurred in warmer conditions than for the high-density treatment, indicating that the intensity of intraspeciÞc competition varies with temperature. Our data show that changes to the temperature regimen can alter grasshopper performance and determine the intensity of intraspeciÞc competition. However, the effects of temperature on grasshopper performance varied with density. Our data indicate the importance of the biotic context in mediating species responses to climatic factors associated with global change.

Evolutionary Ecology, Nov 1, 1997

I address the selection of plants with dierent characteristics by herbivores of dierent body size... more I address the selection of plants with dierent characteristics by herbivores of dierent body sizes by incorporating allometric relationships for herbivore foraging into optimal foraging models developed for herbivores. Herbivores may use two criteria in maximizing their nutritional intake when confronted with a range of food resources: a minimum digestibility and a minimum cropping rate. Minimum digestibility should depend on plant chemical characteristics and minimum cropping rate should depend on the density of plant items and their size (mass). If herbivores do select for these plant characteristics, then herbivores of dierent body sizes should select dierent ranges of these characteristics due to allometric relationships in digestive physiology, cropping ability and nutritional demands. This selectivity follows a regular pattern such that a herbivore of each body size can exclusively utilize some plants, while it must share other plants with herbivores of other body sizes. I empirically test this hypothesis of herbivore diet selectivity and the pattern of resource use that it produces in the ®eld and experimentally. The ®ndings have important implications for competition among herbivores and their population and community ecology. Furthermore, the results may have general applicability to other types of foragers, with general implications for how biodiversity is in¯uenced.

Elsevier eBooks, 1995

This chapter discusses the dominance of different regulating factors for rangeland grasshoppers. ... more This chapter discusses the dominance of different regulating factors for rangeland grasshoppers. Developing a unified, conceptual framework that explains population fluctuations presents a fundamental and critical challenge to ecologists. Although, the standard notion is that grasshopper densities are related to annual weather, the population mechanisms associated with weather have not been established. Comparative results on intraspecific competition for food, predation, and abiotic factors that were obtained from common experiments with the most abundant grasshoppers at each site have been summarized in the chapter. The foregoing results indicate the importance of long-term experiments. To develop an integrated perspective, the chapter focuses on demographic responses most likely to exhibit significant density-dependent and -independent effects. An individual's probability of surviving should be a function of initial hatchling density. The density-independent production is set by a female's ability to process food and convert it into young, given food quality and the abiotic environment. Much of the 50-year debate over population limitation arises in part from weaknesses in the available data sets, but largely stems from the desire of ecologists to attribute limitation to a single mechanism studies to indicate that one of the key mechanisms that changes over time and between sites for herbivore populations is the influence of plant quality and quantity. Studies of population dynamics must consider food resources and how they vary over time and space, especially to resolve issues like population limitation and top-down versus bottom-up control.