Effects of Food Chain Length and Omnivory on Population Dynamics in Experimental Food Webs

Morin, Peter J.; Lawler, Sharon P.

doi:10.1007/978-1-4615-7007-3_22

Cited by 33 publications

(37 citation statements)

References 41 publications

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“…Bacteria and a bacteriovorous ciliate Colpidium striatum (hereafter Colpidium) were incubated either with the IG predator Blepharisma americanum (hereafter Blepharisma), or with one of the pure predators Amoeba proteus and Actinosphaerium eichhornii. The results of this experiment, and of similar experiments with other omnivorous and predatory protists (Morin and Lawler 1996), showed no effect of omnivory on IG prey. However, the population dynamics of the omnivore were always more stable than the dynamics of the pure predators.…”

Section: Experimental Tests Of Early Predictionssupporting

confidence: 64%

Stability and persistence of food webs with omnivory: Is there a general pattern?

et al. 2012

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Abstract. The relationship between omnivory and stability has been the subject of a longstanding debate in ecology. Early theory predicted that omnivory would decrease the probability of food webs being stable. While early empirical data appeared to support the prediction that omnivory should be rare, detailed study of food webs later revealed that omnivory is ubiquitous across ecosystems and taxa. Recent years have seen renewed interest in the omnivory-stability debate, and advances in mechanistic non-equilibrium models demonstrated that omnivory can both increase and decrease stability. Current efforts have therefore focused on identifying biological mechanisms that promote the persistence of food webs with omnivory. We synthesize recent evidence that omnivory often stabilizes food webs when it occurs as life-history omnivory, when prey experience reduced predation rates due to refuges or adaptive antipredator defences, and when omnivores interfere with each other or feed adaptively. Empirical research has lagged behind theory and there remains a shortage of studies directly measuring the stability of diverse natural communities that vary in the number and strength of omnivorous interactions. Early microcosm experiments indicated a narrow range of conditions for the persistence of simple omnivorous modules, while studies of omnivory embedded within larger natural networks have demonstrated its stabilizing effects. These new findings alter our view of food web dynamics and show that rather than looking for a simple and general omnivory-stability relationship, we should focus on identifying conditions under which omnivory is a stabilizing feature of more complex natural systems.

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Section: Experimental Tests Of Early Predictionssupporting

confidence: 64%

Stability and persistence of food webs with omnivory: Is there a general pattern?

et al. 2012

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“…In this system, bacteria are prey for both intermediate consumers and top predators, though their importance in the mosquito diet is unknown. Indirect eVects (e.g., intraguild predation) may counteract direct eVects (Morin and Lawler 1996), and these competing inXuences cannot be distinguished by eVect size calculations. Bottom-up eVects were more important for the numerically dominant middle trophic level group at each site, protozoa in MI and rotifers in FL, whereas top-down eVects were more important for the subdominant group, rotifers in MI and protozoa in FL (Fig.…”

Section: Comparing Relative Evect Size Between Michigan and Floridamentioning

confidence: 99%

“…The system is small, relatively simple, easily manipulated, and replicable (each leaf) (Miller and Kneitel 2005). Simple aquatic food webs have been proposed as model systems for studying food webs (Morin and Lawler 1996), and this system is particularly applicable because it is a natural community, not a laboratory construct (Srivastava et al 2004). In addition, the food web is well suited to experiments manipulating top-down and bottom-up forces.…”

mentioning

confidence: 99%

Relative importance of top-down and bottom-up forces in food webs of Sarracenia pitcher communities at a northern and a southern site

Hoekman

2010

Oecologia

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The relative importance of resources (bottom-up forces) and natural enemies (top-down forces) for regulating food web dynamics has been debated, and both forces have been found to be critical for determining food web structure. How the relative importance of top-down and bottom-up forces varies between sites with different abiotic conditions is not well understood. Using the pitcher plant inquiline community as a model system, I examine how the relative importance of top-down and bottom-up effects differs between two disparate sites. Resources (ant carcasses) and top predators (mosquito larvae) were manipulated in two identical 4 × 4 factorial press experiments, conducted at two geographically distant sites (Michigan and Florida) within the range of the purple pitcher plant, Sarracenia purpurea, and the aquatic community that resides in its leaves. Overall, top predators reduced the density of prey populations while additional resources bolstered them, and the relative importance of top-down and bottom-up forces varied between sites and for different trophic levels. Specifically, top-down effects on protozoa were stronger in Florida than in Michigan, while the opposite pattern was found for rotifers. These findings experimentally demonstrate that the strength of predator-prey interactions, even those involving the same species, vary across space. While only two sites are compared in this study, I hypothesize that site differences in temperature, which influences metabolic rate, may be responsible for variation in consumer-resource interactions. These findings warrant further investigation into the specific factors that modify the relative importance of top-down and bottom-up effects.

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“…Additionally, the ESM assumes that omnivory (feeding on more than one trophic level) can be ecologically important, while the N / PM assumes that omnivory is ecologically insignificant. Mounting evidence suggests that omnivory can be a powerful structuring force (Persson et al, 1988;Diehl, 1992Diehl, , 1993Lawler and Morin, 1993;Menge et al, 1986a;Morin and Lawler, 1996;Persson, 1999;Polis, 1999). In addition, within-and between-trophic level heterogeneity, size-structured interactions, and behaviorally-mediated interactions can all lead to departures from the alternating-control expectations of the N / PM (e.g.…”

Section: Theorymentioning

confidence: 99%

Top-down and bottom-up community regulation in marine rocky intertidal habitats

Menge

2000

Journal of Experimental Marine Biology and Ecology

414

322

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Effects of Food Chain Length and Omnivory on Population Dynamics in Experimental Food Webs

Cited by 33 publications

References 41 publications

Stability and persistence of food webs with omnivory: Is there a general pattern?

Stability and persistence of food webs with omnivory: Is there a general pattern?

Relative importance of top-down and bottom-up forces in food webs of Sarracenia pitcher communities at a northern and a southern site

Top-down and bottom-up community regulation in marine rocky intertidal habitats

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