Dynamics of two Montana grasshopper populations: relationships among weather, food abundance and intraspecific competition

Belovsky, Gary E.; Slade, Jennifer B.

doi:10.1007/bf00328826

Cited by 119 publications

(134 citation statements)

References 42 publications

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“…Thus, smaller grasshoppers must spend considerable effort seeking high-quality plant resources that tend to be comparatively rare (19,20). Experiments have revealed that this can lead to heightened starvation mortality of individuals in small size classes owing to greater intraspecific competition for food resources (20,21).…”

Section: Discussionmentioning

confidence: 99%

Linking individuals with ecosystems: Experimentally identifying the relevant organizational scale for predicting trophic abundances

Ovadia

Schmitz

2002

Proc. Natl. Acad. Sci. U.S.A.

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Ecosystems are complex owing to the fact that emergent properties like trophic structure and productivity depend on details related to lower-scale interactions among individuals. A key challenge is identifying how much individual-level detail is needed to predict patterns at the ecosystem level. We tested for the effect of individual herbivore body size on trophic interactions and consequent abundances of plant and herbivore trophic levels in a New England meadow ecosystem. Body size is an important determinant of vulnerability to predation and thus should influence the way individuals tradeoff time spent foraging against time spent avoiding contact with predators. Such tradeoffs can then influence the degree of damage herbivores inflict on their plant resources. We experimentally assigned field-caught grasshoppers to three distinct body size treatment groups (small, normal, and large) and crossed them with two spider predator treatments (spider present and absent) in a fully replicated design. We observed size-dependent differences in grasshopper survival and development. Moreover, predators caused grasshoppers to inflict greater damage to herbs and lesser damage to grasses relative to treatments without predators. However, there were no size-dependent differences in net damage level on grasses and herbs in either predator or no predator treatments owing to size-dependent compensation in grasshopper foraging effort. We thus conclude that in this ecosystem the foraging-predation risk tradeoff displayed by typical or average-sized herbivore is a sufficient amount of individual-level detail needed to explain ecosystem patterns.size-dependent predation risk ͉ herbivore-mediated trophic effects ͉ old-field ecosystem ͉ grasshoppers ͉ trait-mediated indirect effects E cosystems are paradigmatically complex. They contain many different components that interact directly and indirectly in integrated networks (1, 2). In such complex networks, higher scale system properties like trophic structure, nutrient fluxes, and productivity emerge from lower scale interactions and selection among components (1, 2). Furthermore, feedback loops in which higher scale properties modify lower-scale interactions cause new emergent properties to arise over time (1, 2). A central problem is identifying which lower scale processes should be included in theory aiming to predict higher-scale properties of ecosystems.Classical ecology (e.g., refs. 3-6) has approached this problem by assuming that it is sufficient to abstract lower scale details, such as interactions among individuals in populations, and characterize ecosystem function simply in terms of net changes in numbers or densities of individuals at the level of whole populations. Abstracting such individual-scale detail is reasonable if the effects of individual-level interactions attenuate on the time scale of changes in population density. However, the assumption that individual-scale detail can be safely abstracted is increasingly being called into question (7). Populations are effec...

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Section: Discussionmentioning

confidence: 99%

Linking individuals with ecosystems: Experimentally identifying the relevant organizational scale for predicting trophic abundances

Ovadia

Schmitz

2002

Proc. Natl. Acad. Sci. U.S.A.

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“…The cages were placed over a frame and sandbags placed around the cage on the horizontal flaps to prevent escapes. Similar cages have been used in numerous grasshopper experiments (Joern & Klucas 1993, Belovsky & Slade 1995, Branson 2010. Based on results from Branson (2010), high grasshopper densities were utilized in the experiment.…”

Section: Methodsmentioning

confidence: 99%

Direct and Indirect Effects of Avian Predation on Grasshopper Communities in Northern Mixed-grass Prairie

Branson

2005

Environ Entomol

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“…Such differences in performance can be caused by changes in resource quality and availability or in the duration of the daily thermal window, as the season progresses (e.g., Stauffer and Whitman 1997 and references therein). For instance, several studies on grasshoppers have documented monotonic reductions in plant food quality and quantity during the growing season (e.g., Joern and Gaines 1990;Belovsky and Slade 1995;Oedekoven and Joern 2000). Consequently, the reproductive capacity of individuals that mature late in the season decreases not only owing to shorter reproductive life span but also because of poorer conditions (Wall and Begon 1987b;Joern and Gaines 1990;Stauffer and Whitman 1997).…”

Section: Discussionmentioning

confidence: 99%

“…Specifically, the indirect effects of resource exploitation (e.g., Grimm and Uchmanski 2002) is the likely mechanism driving density regulation (e.g., causing asymmetric competition, which also influences the withinseason body size distribution; Grimm and Uchmanski 2002). Indeed, empirical observations examining densitydependent effects in grasshoppers found no evidence of direct interference (e.g., Belovsky and Slade 1995;Branson 2003). Therefore, the explicit formulation of within-season dynamics represents a profitable extension of the basic model we described in this study.…”

Section: Discussionmentioning

confidence: 99%

Individual Size Variation and Population Stability in a Seasonal Environment: A Discrete-Time Model and Its Calibration Using Grasshoppers

Filin¹,

Ovadia²

2007

The American Naturalist

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Much recent literature is concerned with how variation among individuals (e.g., variability in their traits and fates) translates into higher-level (i.e., population and community) dynamics. Although several theoretical frameworks have been devised to deal with the effects of individual variation on population dynamics, there are very few reports of empirically based estimates of the sign and magnitude of these effects. Here we describe an analytical model for sizedependent, seasonal life cycles and evaluate the effect of individual size variation on population dynamics and stability. We demonstrate that the effect of size variation on the population net reproductive rate varies in both magnitude and sign, depending on season length. We calibrate our model with field data on size-and density-dependent growth and survival of the generalist grasshopper Melanoplus femurrubrum. Under deterministic dynamics (fixed season length), size variation impairs population stability, given naturally occurring densities. However, in the stochastic case, where season length exhibits yearly fluctuations, size variation reduces the variance in population growth rates, thus enhancing stability. This occurs because the effect of size variation on net reproductive rate is dependent on season length. We discuss several limitations of the current model and outline possible routes for future model development.Keywords: body size, individual variation, population stability, seasonal environment, univoltine lifecycle. Ecological entities are organized hierarchically into different levels of organization, such as the individual, the population, and the community (MacMahon et al. 1987;Allen and Hoekstra 1992;Pickett et al. 1994). The way in which these different organizational levels combine to influence the dynamics of natural systems remains a fundamental research topic in ecology (Lomnicki 1988;Nisbet et al. 1989; Abrams 1995;Levin et al. 1997;. Such research is motivated by the need to understand the level of mechanistic biological detail that must be included in ecological theory as well as how much can be safely abstracted while still achieving biologically faithful and quantitatively accurate descriptions of population and community dynamics.In the past 30 years, ecologists have become increasingly interested in linking individual phenotypic variation (in behavior, morphology, physiology, and life history) to population and community dynamics (e.g., Lomnicki 1978;Metz and Diekmann 1986;Begon and Wall 1987;Ebenman and Persson 1988;Nisbet et al. 1989;Bjørnstad and Hansen 1994;Uchmanski 1999;Schmitz 2000;de Roos et al. 2003). Specifically, many theoretical studies have demonstrated how age, stage, and size structure; cohort effects; and other forms of individual variation (e.g., in developmental and growth rates or in competitive ability) have important consequences for population dynamics, stability, and persistence (e.g., Bellows 1986aBellows , 1986bLomnicki 1988;Bjørnstad and Hansen 1994;de Roos 1997;Uchmanski 2000;Kendall ...

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Dynamics of two Montana grasshopper populations: relationships among weather, food abundance and intraspecific competition

Cited by 119 publications

References 42 publications

Linking individuals with ecosystems: Experimentally identifying the relevant organizational scale for predicting trophic abundances

Linking individuals with ecosystems: Experimentally identifying the relevant organizational scale for predicting trophic abundances

Direct and Indirect Effects of Avian Predation on Grasshopper Communities in Northern Mixed-grass Prairie

Individual Size Variation and Population Stability in a Seasonal Environment: A Discrete-Time Model and Its Calibration Using Grasshoppers

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