The usefulness and generality of the keystone species concept has recently been questioned. We investigated variation in interaction strength between the original keystone predator, the seastar Pisaster ochraceus, and its primary prey, mussels (Mytilus californianus and M. trossulus). The study was prompted by differences in community structure at two low zone sites along the central Oregon coast, Boiler Bay (BB) and Strawberry Hill (SH). Predators, especially seastars, were larger and more abundant at SH than at BB. Further, sessile animals were more abundant and macrophytes were less abundant at SH. Predators were more abundant at wave—exposed sites at both sites, and at SH, sessile invertebrates were more abundant at the wave—exposed location and sand cover was high at the wave—protected location. To test the hypothesis that variation in predation strength explained some of these differences, we examined the seastar—mussel interaction at locations with high and low wave exposure at both sites. Predation intensity was quantified by determining the survival of mussels in clumps (50 mussels per clump, shell length 4—7 cm) transplanted to large plots (18—163 m2) with or without seastars in the low intertidal zone. Predation effects were quantified by determining prey recolonization rates in marked quadrats in the same large plots. Spatial variation in interaction strength was quantified by examining predation at scales of metres (among transplants within plots), 10's of metres (between replicate plots within each exposure at each site), 100's of metres (between wave exposures within locations), and 10 000's of metres (between sites). Temporal variation was evaluated by performing the experiments in 1990 and 1991. The relation between prey (mussel) recruitment and growth to differences in community structure was evaluated by quantifying recruitment density in plastic mesh balls (collectors) and growth of individually marked transplanted mussels, respectively, at each site ° exposure ° tide level combination each month for 4 yr. Predation intensity varied greatly at all spatial scales. At the two largest spatial scales (10's of kilometres, 100's of metres), differences in both survival of transplanted mussels and prey recolonization depended on variation in seastar abundance with site, wave exposure, prey recruitment and growth, and at SH protected, the extent of sand burial. Variation at the two smallest scales (metres, 10's of metres) was high when seastars were scarce and low when seastars were abundant. Transplanted mussels suffered 100% mortality in 2 wk at wave—exposed SH, but took >52 wk at wave—protected BB. Seastar effects on prey recolonization were detected only at the SH wave—exposed site. Here, where prey recruitment and growth were unusually high, the mussel M. trossulus invaded and dominated space within 9 mo. After 14 mo, whelks, which increased in both size and abundance in the absence of Pisaster, arrested this increase in mussel abundance. Similar changes did not occur at other site ° exposure combinations, evidently because prey recruitment was low and possibly also due to whelk predation on juveniles. Longer term results indicate that, as in Washington state, seastars prevent large adult M. californianus from invading lower intertidal regions, but only at wave—exposed, not wave—protected sites. Thus, three distinct predation regimes were observed: (1) strong keystone predation by seastars at wave—exposed headlands; (2) less—strong diffuse predation by seastars, whelks, and possibly other predators at a wave—protected cove, and (3) weak predation at a wave—protected site buried regularly by sand. Comparable experimental results at four wave—exposed headlands (our two in Oregon and two others in Washington), and similarities between these and communities on other West Coast headlands suggest keystone predation occurs broadly in this system. Results in wave—protected habitats, however, suggest it is not universal. In Oregon, keystone predation was evidently contingent on conditions of high prey production (i.e., recruitment and growth), while diffuse predation occurred when prey production was low, and weak predation occurred when environmental stress was high. Combining our results with examples from other marine and non—marine habitats suggests a need to consider a broader range of models than just keystone predation. The predictive and explanatory value of an expanded set of models depends on identifying factors distinguishing them. Although evidence is limited, a survey of 17 examples suggests (1) keystone predation is evidently not distinguished from diffuse predation by any of 11 previously proposed differences, but (2) may be distinguished by rates of prey production. Further, (3) differential predation on competitively dominant prey does not distinguish keystone from nonkeystone systems, since this interaction occurs in both types of community. Instead, differential predation on dominant prey evidently distinguishes strong—from weak—predation communities. While the keystone predation concept has been and will continue to be useful, a broadened focus on testing and developing more general models of community regulation is needed.

The Keystone Species Concept: Variation in Interaction Strength in a Rocky Intertidal Habitat

In this article I examine moose-wolf interactions over a broad spectrum of moose densities with the primary objective to test empirically whether wolf predation can regulate moose numbers. I also present four conceptual models of moose population dy- namics and outline their specific predictions. Based on 27 studies where moose were the dominant prey species, the functional and numerical responses of wolves to changing moose density were derived using an hyperbolic, Michaelis-Menten function. Per capita killing rate was strongly related (P = .01) to moose density, as was the density of wolves (P < .0 1). Killing rate plateaued at 3.36 moose wolf (100 days) I when predators were fully satiated. The asymptotic value for wolf density was 5 8.7 animals/ 1 000 km2. Wolf predation rate, as derived from the total predator response, proved to be density dependent from 0 to 0.65 moose/km2, and inversely density dependent at higher moose densities. Predator: prey ratios reflected wolf predation rate poorly because they did not integrate the functional response. An empirical model based on these results suggests that moose would stabilize at 2.0 moose/km2 in the absence of predators, and at - 1.3 moose/km2 in the presence of a single predator, the wolf. Density-dependent food competition creates these two high- density equilibrium conditions. If moose productivity is diminished through either dete- riorating habitat quality or bear-induced early calf mortality, then a low-density equilibrium (0.2-0.4 moose/km2) is predicted. The model also suggests that when a low equilibrium develops, a "predator pit" is absent or extremely shallow, thus arguing against the appro- priateness of a predation-food two-state model. Further research on the density relationship of bear predation, on the effect of alternate prey on wolf total response, and on the regulatory impact of food competition at high moose densities, is required for a full understanding of moose demography.

Ungulate population models with predation: a case study with the north american moose'

Populations of rodents isolated on islands often show systematic differences in demography, reproduction, behavior, and morphology when compared to mainland populations. These differences, termed the island syndrome, include higher and more stable densities, better survival, increased body mass, and reduced aggressiveness, reproductive output, and dispersal. We synthesize information in the literature on island rodent populations and construct a conceptual model to explain the island syndrome. Population density and other manifestations of the island syndrome are predicted to increase with island isolation and to decrease with island area. The effect of isolation is direct by limiting dispersal, while the effect of area is less direct. As area increases, predators, competitors, and habitat structure increase in diversity. We suggest that the intensity or absence of density-depressing factors (primarily predation in communities comprised of only a few morphologically and trophically divergent species) is primarily responsible for the area effect and serves as a principal factor differentiating island from mainland populations of rodents. Other characteristics associated with the island syndrome may be the result of both short-term and long-term processes or responses. Short-term responses include reproductive, body size, and behavioral changes that may be phenotypic reaction norms in response to higher island densities. Thus, higher densities lead to reduced reproductive output, which then leads to greater body size. Initial behavioral differences may be owing to better survival and reduced dispersal, which result in less population turnover, greater neighbor familiarity, and less aggression. Long-term changes may be due to directional selection for reduced dispersal, increased body size in response to increased intraspecific competition, reduced reproductive output (smaller litters and delayed maturation) in response to reduced mortality schedules, and reduced aggressiveness. While the model is specific to rodent populations, the conclusions may be applicable to other systems if characteristics such as body size, vagility, and community composition are considered.

The island syndrome in rodent populations.

Blue whales Balaenoptera musculus meet the highest prey demands of any predator that has ever existed by feeding exclusively upon dense but patchy schools of pelagic euphausiids. We examined the role that seasonally high primary production supported by coastal upwelling com- bined with topographic breaks off California play in creating, collecting, and maintaining euphausi- ids at densities sufficient to allow exploitation by whales. We used concurrent ship- and mooring- based oceanographic, hydroacoustic, and net sampling, whale-sighting records, visual surveys, and time-depth recorder deployment to examine temporal and spatial linkages between (1) intensity of upwelling, (2) primary production, (3) development, density and distribution of euphausiids, and (4) the distribution, abundance, and foraging behavior of blue whales in Monterey Bay, California between 1992 and 1996. Blue whales fed exclusively upon adult euphausiids Thysanoessa spinifera and Euphausia pacifica that were larger than those generally available in the Bay. Foraging whales dove repeatedly to dense euphausiid aggregations between 150 and 200 m on the edge of the Mon- terey Bay Submarine Canyon. Euphausiid aggregations where whales were foraging averaged 153 g m -3 , approximately 2 orders of magnitude greater than mean euphausiid densities in the Bay (1.3 g m -3 ). High euphausiid densities are supported by high primary production between April and August (249 mgC m -3 d -1 ) and a submarine canyon that provides deep water down-current from an upwelling region. Peak euphausiid densities occur in late summer/early fall, lagging the seasonal increase in primary production by 3 to 4 mo. This lag results from the temporal development of euphausiids spawned around the spring increase in primary production and the shoreward collapse of productivity due to decreased upwelling in late summer. The migratory movements of the Califor- nia blue whale probably reflect seasonal patterns in productivity in other foraging areas similar to those we describe for Monterey Bay.

/pdf/from-wind-to-whales-trophic-links-in-a-coastal-upwelling-1t67qmdtwt.pdf

From wind to whales: trophic links in a coastal upwelling system

Population dynamics of forest rodents, bank voles Clethrionomys glareolus (Schreber, 1780) and yellow-necked mice Apodemus flavicollis (Melchior, 1834) were studied in 1959-1991 in the pristine mature forest dominated by hornbeam Carpinus betulus and oak Quercus robur in Bialowieza National Park (eastern Poland). The whole 33-year series, and particularly the detailed data from 1971-1991, were related to weather data and seed crop of hornbeam, oak, and maple Acer platanoides.

/pdf/rodent-population-dynamics-in-a-primeval-deciduous-forest-19mt7nwyrh.pdf

Rodent population dynamics in a primeval deciduous forest (Białowieża National Park) in relation to weather, seed crop, and predation

Kidd and Lewis (1987) made two critical comments on our paper entitled \"Can vertebrate predators regulate their prey?\" They claimed that the evidence presented for predation-mediated regulation is inconclusive, and they questioned some of the ways we interpreted our data. Their second criticism concerns the dynamics of the examined Microtus population. Kidd and Lewis argued that our data suggest \"the possibility of a population fluctuation, albeit of small amplitude\" (p. 448). We agree on that. Moreover, recent detailed studies based on the mark-recapture method have confirmed that the vole population fluctuates between years and that the numbers in the autumns of different years vary considerably (fig. 1). The point that we have stressed in our papers (Erlinge et al. 1983, 1984), however, is that the vole population in southern Sweden shows a noncyclic pattern, which is the opposite of the pattern characterizing the microtine populations in northern Sweden (Myllymaki 1977; Hansson 1979; Hornfeldt et al. 1986). This difference means less between-year fluctuation in the south (no marked population crash following a year with peak densities) and a characteristic seasonal pattern with peak numbers in autumn and low densities in spring and early summer every year. Our study aimed to explain this difference. Kidd and Lewis's first comment concerns the regulative significance of predation. They argued that population regulation implies density dependence. The predation rate on voles in our study has not been shown to work in a densitydependent way between years, and the delayed density dependence observed over the year would essentially be destabilizing. Kidd and Lewis are right in many of their comments. We were not able to demonstrate any clear evidence for density-dependent predation in our earlier studies. Instead, we found that predation rate was inversely correlated with changes in vole numbers during most of the year (Erlinge et al. 1983, p. 41, fig. 3). We considered two exceptions important, however. Density-dependent predation occurred in autumn toward the end of the reproductive season and in late spring at the beginning of the breeding season. This timing might have a regulating effect on vole numbers between years. Ricklefs, discussing population regulation, concluded that \"for a population to be maintained within narrow limits, stabilizing forces need operate only during a portion of the year that is long enough to

More Thoughts on Vertebrate Predator Regulation of Prey

in an open field area in southern Sweden. Biomass and numbers of hares and pheasants eaten by the predators were calculated from data on food habits, food requirements, and numbers of the mammalian ...

Predation on brown hare and ring-necked pheasant populations in southern Sweden

Hunting in flight by tawny owls strix aluco

Whether vertebrate predators can regulate their prey or not has long been a controversial question. At the one extreme it has been claimed that predators have no impact on prey numbers but consume only a doomed surplus (Errington 1946), and at the other that predators strongly interact with their prey causing either stable equilibria or cycles (Tanner 1975; Keith et al. 1977). However,.there are no field studies showing a regulatory effect of predation among vertebrates. Here we report on such a study.

https://www.jstor.org/stable/pdfplus/2460891.pdf

Can vertebrate predators regulate their prey

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

Ingvar N. Nilsson

Author Tools

Chat about Author

Papers

More Thoughts on Vertebrate Predator Regulation of Prey

Predation on brown hare and ring-necked pheasant populations in southern Sweden

Hunting in flight by tawny owls strix aluco

Can vertebrate predators regulate their prey