Generalist Natural Enemies Research Articles

The Strength of Biological Control in the Battle against Invasive Pests: a Reply

The Strength of Biological Control in the Battle against Invasive Pests: a Reply MARK S. HODDLE Department of Entomology, University of California–Riverside, Riverside, CA 92521, U.S.A., email mark.hoddle@ucr.edu Nontarget Impacts of Biological Control Louda and Stiling (2004 [this issue]) state that biological control is not a simple matter of community re-assemblage because deliberate introductions of exotic natural ene- mies for suppression of exotic pest populations can have reticulate impacts that are difficult, if not impossible, to predict a priori. In an insightful retrospective study, Hawkins et al. (1999) analyzed 68 life-table studies of native insects and introduced insect pests to determine whether biological control is analogous to naturally oc- curring control (i.e., the action of native natural enemies on native hosts). Hawkins et al. (1999) show that suc- cessful biological control programs result in less reticulate trophic relationships than those seen in natural food webs of native insects. The most successful biological control programs are those that do not have “natural” food-web structures because biological control food webs consist of short, linear food chains that are devoid of complex reticulate trophic interactions. This result occurs because biological control systems often consist of exotic species that share few ecologi- cal or evolutionary links with native biota. Furthermore, control is enhanced in simplified habitats characteristic of agroecosystems and, arguably, native systems invaded by exotic plants because both often consist of vast mono- typic stands of exotic vegetation. Host-specific natural en- emies that cause population declines of the target pest are themselves subject to density-dependent population regulation as the biological control agent’s food source is depleted, and they are unable to adequately exploit other hosts in the environment to maintain high population densities because they lack significant trophic linkages to other hosts. The more specialized the natural enemy the less likely it is to infiltrate native communities and attack nontarget native species (Hennemen & Memmott 2001). Generalist natural enemies that have low levels of host and habitat fidelity and exploit a wide range of hosts in a vari- ety of habitats are more likely to cause unwanted collat- eral damage to nontarget species either directly through direct attack or indirectly through apparent competition because of reticulate food-web linkages. Two plant-feeding insects (Rhinocyllus conicus [inten- tionally released; Gassmann & Louda 2001] and Larinus planus [an accidental arrival in the United States that was eliminated as a potential biological control agent because of broad host breadth on Carduinae thistles in its home range; Louda & O’Brien 2002]) mentioned by Louda and Stiling as having “unexpected levels of nontarget feeding” were anticipated from host-specificity tests because both weevils were known to feed and reproduce on a variety of thistle species in their home and introduced range. As Louda and Stiling point out, both insects are “thistle specialists,” but thistles are a speciose group with repre- sentatives in genera that occur in Europe and North Amer- ica, and these weevils, due to their broad dietary breadth within the thistle group, have greater numbers of signif- icant food-web linkages than desirable, thereby making significant nontarget impacts more likely. The real issue here concerns legislation (i.e., redistribution of L. planus and R. conicus) and changing social values (i.e., what con- stituted acceptable damage to nontarget species, and the value of native flora and fauna in the 1960s versus 2003), as opposed to an inherent flaw in the theoretical prin- ciples underlying concepts of host specificity and host range assessment as they pertain to biological control. The moth Cactoblastis cactorum, a native of Argentina and “poster child” of biological control (Stiling 2002) has invaded the continental United States from the Caribbean and is attacking native cactii. Louda and Stiling consider C. cactorum a “specialist” on the cactus genus Opuntia, a group with approximately 200 species in the new world but no representatives in Australia, making C. cactorum a specialist on this continent when it was released in Paper submitted April 15, 2003; revised manuscript accepted May 23, 2003. Conservation Biology, Pages 61–64 Volume 18, No. 1, February 2003

Restoring Balance: Using Exotic Species to Control Invasive Exotic Species

Abstract: Invasive species threaten natural habitats worldwide, and active human management is required to prevent invasion, contain spread, or remediate ecosystems following habitat degradation. One powerful technology for invasive species management in sensitive habitats is biological control, the use of carefully selected upper‐trophic‐level organisms that utilize the exotic pest as a resource, thereby reducing it to less harmful densities. Many in the conservation biology community view this pest‐management technology as a high‐risk enterprise because of potential collateral damage to nontarget species. The potential benefits arising from successful biological programs are reduced pesticide use, significant pest suppression, and a return to ecological conditions similar to those observed before the arrival of the pest. Biological control as a pest‐management strategy has limitations: some pest species may not be suitable targets for biological control because natural enemies may not be sufficiently host‐specific and may pose a threat to nontarget organisms. In some instances, substantial effects on nontarget species have occurred because generalist natural enemies established as part of a biological control program heavily utilized other resources in addition to the target pest. To minimize nontarget impacts, regulations governing releases of natural enemies are becoming more stringent, as evidenced in New Zealand and Australia. Voluntary codes of good practice are being advocated by the Food and Agriculture Organization to promote wide adoption of safety measures, which, if followed, should result in the selection of agents with high levels of host and habitat fidelity. Biological control programs in support of conservation have traditionally targeted weed species that threaten natural areas. More recently, exotic arthropod pests that compete with native wildlife or damage native plants have become targets of conservation‐oriented biological control programs. Extension of biological control to new targets of conservation importance, such as invasive aquatic invertebrates and pestiferous vertebrates, is warranted. In many instances, once prevention, containment, and eradication options have been exhausted or deemed infeasible, carefully orchestrated biological control programs against appropriately selected targets may be the only feasible way to control invasive species affecting communities under assault from exotic species.

Acarine pests of citrus: overview and non-chemical control

The mites that feed on citrus, which belong to the families Tetranychidae, Tenuipalpidae and Eriophyidae, along with a single species in the Tarsonemidae, are listed and ranked according to their injury. All major citrus pests, except the Eriophyidae, are generalists. Analogously, there are only generalists, but no specialists, among the natural enemies that are known, or postulated, to control acarine citrus pests. This suggests that neither the major pest mites nor their natural enemies have evolved on citrus, and that generalist predators thus have a better chance to control the pests. As the introduction of generalist natural enemies is currently restricted by environmental concerns, and as this practice has not led to improved control of the acarine pests of citrus, it is argued that better use should be made of the indigenous predators of citrus mites.

Natural enemy specialization and the period of population cycles

AbstractThe dynamical consequences of multiple‐species interactions remain an elusive and fiercely debated topic. Recently, Murdoch and colleagues proposed a general rule for the dynamics of generalist natural enemies: when periodic, they exhibit single generation cycles (SGCs), similar to single species systems. This contrasts markedly with specialists, which tend to show classic (longer period) consumer–resource cycles. Using a well‐studied laboratory system, we show that this general rule is contradicted when we consider resource age‐structure.

Specific foraging kairomones used by a generalist parasitoid.

In general, it is assumed that generalist natural enemies do not innately use specific cues for the location of their host or prey species. This hypothesis was tested using naïve females of the generalist parasitoid Lariophagus distinguendus Förster and two of its hosts, larvae of the lesser grain borer Rhyzopertha dominica (F.) and of the granary weevil Sitophilus granarius L., feeding in wheat grains. In a four-chamber olfactometer, female parasitoids were attracted to volatiles emanating from the feces of both host species. Chemical analysis of the volatiles from the feces of R. dominica revealed the presence of dominicalure 1 and 2, the species specific aggregation pheromones of R. dominica. The main compounds in the volatiles from feces of S. granarius were identified as chemicals related to mites that are associated with hosts of L. distinguendus. Because these mites are not specific for S. granarius but also co-occur with other hosts, the mite chemicals have to be considered as general cues. In bioassays, synthetic dominicalure was attractive to naïve L. distinguendus, explaining the attraction of feces volatiles from R. dominica. Synthetic mite chemicals and sitophilate, the aggregation pheromone of S. granarius, had no effect on naïve parasitoids. It remains to be determined which innate chemical cues from feces of S. granarius are used by L. distinguendus. In contrast to our initial hypothesis, the generalist L. distinguendus is innately using specific cues for foraging. Two ideas are provided to explain this result.

INTERACTIONS BETWEEN SPECIALIST AND GENERALIST NATURAL ENEMIES: PARASITOIDS, PREDATORS, AND PEA APHID BIOCONTROL

Most biological control systems involve a diverse community of natural enemies. We investigated how specialist and generalist natural enemies differ as biological control agents of pea aphids (Acyrthosiphon pisum), and how interactions among natural enemies affect successful control. In alfalfa, pea aphids are attacked by a specialist parasitoid wasp, Aphidius ervi, and a guild of generalist predators primarily made up of Nabis and Orius bugs, coccinellid and carabid beetles, and web-building spiders. In three field experiments, we manipulated the parasitoid, then the generalist predator guild, and finally both classes of natural enemy, and recorded resulting impacts on pea aphid population control. The parasitoid caused little immediate reduction in aphid population growth but caused a large decline after a delay corresponding to the generation time of the parasitoid. In contrast, the generalist guild caused an immediate decline in the aphid population growth rate. However, the generalists did not exert density-dependent control, so aphid densities continued to increase throughout the experiment. The third field experiment in which we simultaneously manipulated parasitoids and predators investigated the possibility of “nonadditive effects” on aphid control. Densities of parasitoid pupae were 50% lower in the presence of generalist predators, indicating intraguild predation. Nonetheless, the ratio of parasitoids to aphids was not changed, and the impact of the two types of natural enemies was additive. We constructed a stage-structured model of aphid, parasitoid, and predator dynamics and fit the model to data from our field experiments. The model supports the additivity of parasitoid and predator effects on aphid suppression but suggests that longer-term experiments (32 d rather than 20 d) would likely reveal nonadditive effects as predation removes parasitoids whose response to aphid densities occurs with a delay. The model allowed us to explore additional factors that could influence the additivity of parasitoid and predator effects. Aphid density-dependent population growth and predator immigration in response to aphid density would likely have little influence on the additivity between parasitism and predation. However, if a parasitoid were to show a strong Type II functional response, in contrast to A. ervi whose functional response is nearly Type I, interactions with predators would likely be synergistic. These analyses reveal factors that should be investigated in other systems to address whether parasitism and predation act additively on host densities. Corresponding Editor: E. Evans.

Specialist and generalist natural enemies as an explanation for geographical gradients in population cycles of northern herbivores

Within Fennoscandia, two well‐studied groups of herbivores exhibit clear geographical gradients in their population dynamics. Populations of a forest lepidopteran (Epirrita autumnata, the autumnal moth) and voles of the genera Microtus and Clethrionomys show pronounced multi‐annual cycles in the north but become more stable towards the south. Here we review empirical and theoretical studies on these species, mainly regarding the biological mechanisms that are assumed to generate the pattern of population dynamics in both systems. We conclude that the specialist/generalist predation hypothesis offers a common explanation for the population cycles and their geographical gradients irrespective of whether a herbivorous insect or small mammals are concerned. According to this hypothesis, originally developed for the Fennoscandian voles, but now applied also to E. autumnata, population cycles are generated by specialist natural enemies (predators for the voles and parasitoids for E. autumnata). Furthermore, the dynamic shift from cycles to stability is assumed to be caused by an increase in the density and diversity of generalist natural enemies from north to south in Fennoscandia.

Enhancing Biological Control: Habitat Management to Promote Natural Enemies of Agricultural Pests

Over the past ten years an increasing number of field entomologists and farmers have recognized that conservation of natural enemies is important to effective biological control in many agricultural systems. This collection addresses an important gap in the biological control literature by providing the first comprehensive summary of recent findings on habitat manipulation to control pests. Enhancing Biological Control includes contributions from experts around the world: the United States, Finland, Germany, Great Britain, People's Republic of China, and Switzerland. Chapters cover habitat modification in such areas as fields, orchards, or vineyards, and along or near the perimeters of fields, including hedges or other uncultivated areas. Generalist and specialist natural enemies are described in full, as are theoretical and practical issues. Experimental designs for studying enhancement come into play, and the editors include a modeling study that explores how the dispersal of natural enemies interacts with the positioning of refuges. This volume is an invaluable source of information to researchers, progressive farmers, and agricultural consultants.

Enemy-free space via host plant chemistry and dispersion: assessing the influence of tri-trophic interactions.

It has been argued that generalist natural enemies of insect herbivores provide a major selection pressure for restricted host plant range. This idea is a subset of the enemy-free space (EFS) hypothesis, whereby insect herbivores escape their enemies by being scarce in space and time and/or chemically defended via containing plant allelochemicals. To date, there are only two complete tests of EFS via host plant chemistry and two via host plant dispersion, and only two of these tests support the EFS hypothesis. However, three corollaries to existing views on EFS are sufficiently supported by data to warrant direct testing of the view that EFS is obtained via host plant chemistry's effects on enemies of insect herbivores. So the issue remains. Resolution will require a more collaborative, methodological approach to examine the relative importance of the major multiple factors that shape patterns of feeding specialization of insect herbivores. Predation is certainly one of these factors, but its role is still not clear.

Phylogenetic evidence for the evolution of ecological specialization in Timema walking-sticks

Abstract We used phylogenetic and ecological information to study the evolution of host-plant specialization and colour polymorphism in the genus Timema, which comprises 14 species of walking-sticks that are subject to strong selection for cryptic coloration on their host-plants. Phylogenetic analysis indicated that this genus consists of three main lineages. Two of the lineages include highly generalized basal species and relatively specialized distal species, and one of the lineages comprises four specialized species. We tested for phylogenetic conservatism in the traits studied via randomizing host-plant use, and the four basic Timema colour patterns, across the tips of the phylogeny, and determining if the observed number of inferred changes was significantly low compared to the distribution of numbers of inferred changes expected under the null model. This analysis showed that (1) host-plant use has evolved nonrandomly, such that more closely related species tend to use similar sets of hosts and (2) colour pattern evolution exhibits considerable lability. Inference of ancestral states using maximum parsimony, under four models for the relative ease of gain and loss of plant hosts or colour morphs, showed that (1) for all models with gains of host-plants even marginally more difficult than losses, and for most optimizations with gains and losses equally difficult, the ancestral Timema were generalized, feeding on the chaparral plants Ceanothus and Adenostoma and possibly other taxa, and (2) for all models with gains of colour morphs more difficult than losses, the ancestral Timema were polymorphic for colour pattern. Generation of null distributions of inferred ancestral states showed that the maximum-parsimony inference of host-plant generalization was most robust for the most speciose of the three main Timema lineages. Ancestral states were also inferred using maximum likelihood, after recoding host-plant use and colour polymorphism as dichotomous characters. Likelihood analyses provided some support for inference of generalization in host-plant use at ancestral nodes of the two lineages exhibiting mixtures of generalists and specialists, although levels of uncertainty were high. By contrast, likelihood analysis did not estimate ancestral colour morph patterns with any confidence, due to inferred rates of change that were high with respect to speciation rates. Information from biogeography, floristic history and the timing of diversification of the genus are compatible with patterns of inferred ancestral host-plant use. Diversification in the genus Timema appears to engender three main processes: (1) increased specialization via loss of host-plants, (2) retention of the same, single, host-plant and (3) shifts to novel hosts to which lineages were ‘preadapted’ in colour pattern. Our evidence suggests that the radiation of this genus has involved multiple evolutionary transitions from individual-level specialization (multiple-niche polymorphism) to population-level and species-level specialization. Ecological studies of Timema suggest that such transitions are driven by diversifying selection for crypsis. This paper provides the first phylogeny-based evidence for the macroevolutionary importance of predation by generalist natural enemies in the evolution of specialization.

Can natural enemies enforce geographical range limits?

We develop a simple mathematical model to investigate the question as to whether a specialised consumer can be responsible for creating a range limit in the population of its dynamic resource. The model is most attuned for parasitoid‐host relationships, but the central results should apply to a broad range of systems. Specifically, at the beginning of each simulation host and parasitoid populations are distributed at random along a string of patches. In each discrete generation and for each patch, host and parasitoid populations grow and interact, and then a constant fraction of those remaining disperses one or more patch distances in either direction according to a geometric distribution. We iterate the model 200 generations, and in any generation for any patch, either host and/or parasitoid can go locally extinct if its population falls below a threshold density. We find that a specialised parasitoid can enforce a limit, and it is even more likely to fragment its host population. The two most important conditions for parasitoid‐enforced range limits are: 1) the theoretical host equilibrium density in the presence of the parasitoid be very small at sites eliminated from the host's range, and 2) the parasitoid disperses at high rates. We close by discussing our findings for specialist and generalist natural enemies, and the relevance of our study to the wealth of investigations on the causes of geographical range limits.

Perspective of practical biological control and population theories

AbstractWe have not yet had sufficient theoretical explanation for successful biological control in which a key pest is controlled after an introduction of natural enemies. I compare here real features of successful biological control and theoretical host–parasitoid population models to reduce the gap between theory and practice. I first review the historical interaction between classical biological control projects and theoretical population models. Second, I consider the importance of host refuges in host–parasitoid population dynamics as concerns the mechanisms of low and stable host density. The importance of density–dependent parasitism through parasitoid reproduction in multivoltine host–parasitoid systems and supplemental generalist natural enemies are also discussed. Finally, I consider the difference in tactics for classical biological control and for augmentation of natural enemies in annual crop systems.

Manipulating carabid beetle abundance alters prey removal rates in corn fields

Generalist natural enemies such as carabid beetles have the potential to maintain a variety of pests below outbreak levels in annual crops. To assess the relationship between carabid beetle abundance and field rates of prey removal, we created plots surrounded by different boundaries that selectively affected dispersal of edaphic arthropods, primarily carabids. Three treatments were established: (1) naturally occurring communities, (2) augmented communities using ingress boundaries, and (3) reduced communities using egress boundaries. Selective boundaries altered carabid communities with minimal habitat alteration and without use of insecticides. Three times during the growing season, a fixed number of onion fly pupae were placed in plots to evaluate the impact of carabid abundance on predation rates. A combination of vertebrate and invertebrate exclosures allowed us to evaluate prey removal by invertebrates alone. In comparison to the no boundary treatment, carabids increased 54.2% and decreased 83.1% in plots surrounded by ingress and egress boundaries respectively. Predation rates were positively correlated with carabid abundance (r2 = 0.70, p < 0.0001). Significantly more pupae were removed from exclosures allowing access to invertebrates alone than from total exclosures, suggesting that invertebrates represented an important group of predators. Laboratory trials tested the feeding potential of the four most abundant carabid species and showed that they readily consumed onion fly pupae, supporting our hypothesis that carabids were the main predators in field tests. This study corroborates and extends previous observations of the importance of carabid beetles as generalist predators of insect pests in agricultural fields.

Manipulating Natural Enemies By Plant Variety Selection and Modification: A Realistic Strategy?

The host plants of arthropod pests may affect parasitoids and predators directly or indirectly, through multitrophic interactions. Direct plant effects may involve simple mechanisms such as reduced parasitoid searching efficiency caused by trichomes. Multitrophic effects often involve complex interactions that are not well understood, and their impact on natural enemies and biological control are difficult to predict. Knowledge of the direct and multitrophic effects creates opportunities to increase the effectiveness of natural enemies by incorporating natural enemy-enhancing traits into crop plants. The strategy may have potential for both generalist and specialist natural enemies, but the enemies' behavior and other factors will affect the results. Although combining natural enemies and plant resistance may slow the adaptation of some insect pests, it may speed up adaptations of others. A better understanding of plant/pest/natural enemy evolution is necessary to predict how to combine natural enemies and plant resistance for the best long-term results.

Managing Tropical Rice Pests Through Conservation of Generalist Natural Enemies and Alternative Prey

The cultivation of tropical Asian rice, which may have originated 9000 yr ago, represents an agricultural ecosystem of unrivaled ecological complexity. We undertook a study of the community ecology of irrigated tropical rice fields on Java, Indonesia, as a supporting study for the Indonesian National Integrated Pest Management Programme, whose purpose is to train farmers to be better agronomists and to employ the principles of integrated pest management (IPM). Two of our study objectives, reported on here, were (1) to explore whether there exist general and consistent patterns of arthropod community dynamics related to natural or intrinsic levels of biological control, and (2) to understand how the existing levels of biological control are affected by insecticide use, as well as by large—scale habitat factors relating to differing patterns for vegetational landscapes, planting times, and the length of dry fallow periods. We performed a series of observational studies and two experimental studies. Abundant and well—distributed populations of generalist predators can be found in most early—season tropical rice fields. We took samples from plants and water surface using a vacuum—suction device, and from the subsurface using a dip net. Our results show that high populations of generalist predators are likely to be supported, in the early season, by feeding on abundant populations of detritus—feeding and plankton—feeding insects, whose populations consistently peak and decline in the first third of the season. We hypothesize that since this abundance of alternative prey gives the predator populations a "head start" on later—developing pest populations, this process should strongly suppress pest populations and generally lend stability to rice ecosystems by decoupling predator populations from a strict dependence on herbivore populations. We experimentally tested our hypothesis of trophic linkages among organic matter, detritivores and plankton feeders, and generalist predators and showed that by increasing organic matter in test plots we could boost populations of detritivores and plankton—feeders, and in turn significantly boost the abundance of generalist predators. These results hold for populations found on the plant, on the water surface, and below the water surface. We also demonstrated the link between early—season natural enemy populations and later—season pest populations by experimentally reducing early—season predator populations with insecticide applications, causing pest populations to resurge later in the season. Overall, these results demonstrate the existence of a mechanism in tropical irrigated rice systems that supports high levels of natural biological control. This mechanism depends on season—long successional processes and interactions among a wide array of species, many of which have hitherto been ignored as important elements in a rice ecosystem. Our results support a management strategy that promotes the conservation of existing natural biological control through a major reduction in insecticide use, and the corresponding increase in habitat heterogeneity.

Spatial Heterogeneity and the Population Dynamics of a Host--Parasitoid System

The cabbage root fly, Delia radicum, at Silwood Park is attacked by both generalist and specialist natural enemies. This paper uses spatial and temporal census data to examine the relative contributions of these natural enemies to the population dynamics of D. radicum. Data on the distributions and mortalities of D. radicum on 40 swede plants in nine consecutive years have been analysed. Using a maximum likelihood technique, the parameters (together with their support limits) have been estimated from these data for a model of an insect host - generalist - specialist interaction. Three particular cases of the model are analysed: (i) only the generalist, Aleochara bilineata, is present; (ii) only the specialist, Trybliographa rapae, is present; and (iii) both species of natural enemy are present

How many species are there in apple insect communities?: testing the resource diversity and intermediate disturbance hypotheses

Abstract. In European and American apple orchards the insect species richness, calculated from our own, and published data, varied widely (30–940 species). The dominance of insect orders was similar to that found in natural communities. To test the predictions of the‘resource diversity hypothesis’(RDH) and the‘intermediate disturbance hypothesis’(IDH) of insect diversity, we analysed the simultaneous impact of vegetational diversity and intensity of orchard management practice on the species richness of characteristic insect categories in six types of apple stands, over 5 years, in Hungary. The more diverse was the vegetation adjacent to the orchard and the less intensively was the orchard managed, the greater was the total insect species richness, supporting both hypotheses. The number of agricultural pest species found in the apple orchards depended above all on the diversity of adjacent agricultural vegetation, supporting only the RDH. The species richness of specialized apple pests was limited only by the intensity of pest control, supporting only the IDH. Within the category of generalist natural enemies species richness mainly varied with the diversity of adjacent vegetation, supporting the RDH. The aeroentomofauna constituted a surprisingly high percentage (&gt;50%) for both total species and agricultural pests, but was poorly represented within the natural enemies category, and absent from the specific apple pest category. A general conclusion is that the number of insect species in perennial orchard‐systems within agricultural areas is determined primarily by the regional extra‐orchard vegetational diversity and secondly by the degree of local intra‐orchard disturbances and plant diversity. Consequently, at the community level the predictions of both hypotheses can be simultaneously valid at different spatial scales and are not mutually exclusive. However, within the community, at the level of the different insect categories studied here, only one of the hypotheses proved to be valid.

Host range in phytophagous insects: the potential role of generalist predators

The potential role of generalist natural enemies is presented as one of the important ecological pressures that select for narrow host range in phytophagous insects, and dominant relative to physiological bases for specialization. Experiments are described in three completely different systems indicating that generalist herbivores are more vulnerable to predation than specialist herbivores. The three predators were (a) the vespid waspMischocyttarus flavitarsus, (b) the Argentine antIridomyrmex humilis and (c) the coccinellid beetleHippodamia convergens. It is concluded the predators may provide strong selection pressure for maintenance and perhaps evolution of narrow host range in insect herbivores.

On the Evolution of Host Specificity in Phytophagous Arthropods

We argue that generalist natural enemies of herbivorous insects provide a major selection pressure for restricted host plant range. The significance of plant chemistry is discussed in terms of regulating behavior, while the chemical coevolutionary theories are considered to be of limited value.

More Thoughts on Vertebrate Predator Regulation of Prey

Previous articleNext article No AccessNotes and CommentsMore Thoughts on Vertebrate Predator Regulation of PreySam Erlinge, Gorgen Goransson, Goran Hogstedt, Goran Jansson, Olof Liberg, Jon Loman, Ingvar N. Nilsson, Torbjorn von Schantz, and Magnus SylvenSam Erlinge Search for more articles by this author , Gorgen Goransson Search for more articles by this author , Goran Hogstedt Search for more articles by this author , Goran Jansson Search for more articles by this author , Olof Liberg Search for more articles by this author , Jon Loman Search for more articles by this author , Ingvar N. Nilsson Search for more articles by this author , Torbjorn von Schantz Search for more articles by this author , and Magnus Sylven Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 132, Number 1Jul., 1988 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/284842 Views: 3Total views on this site Citations: 21Citations are reported from Crossref Copyright 1988 The University of ChicagoPDF download Crossref reports the following articles citing this article:Anders Pape Møller, Timothy A. Mousseau Assessing effects of radiation on abundance of mammals and predator–prey interactions in Chernobyl using tracks in the snow, Ecological Indicators 26 (Mar 2013): 112–116.https://doi.org/10.1016/j.ecolind.2012.10.025Alexandre Millon, Jan Tøttrup Nielsen, Vincent Bretagnolle, Anders Pape Møller Predator-prey relationships in a changing environment: the case of the sparrowhawk and its avian prey community in a rural area, Journal of Animal Ecology 78, no.55 (Jul 2009): 1086–1095.https://doi.org/10.1111/j.1365-2656.2009.01575.xCornelia Kraus, Heiko G. Rödel Where have all the cavies gone? Causes and consequences of predation by the minor grison on a wild cavy population, Oikos 105, no.33 (Jun 2004): 489–500.https://doi.org/10.1111/j.0030-1299.2004.12941.xA. R. E. Sinclair Mammal population regulation, keystone processes and ecosystem dynamics, Philosophical Transactions of the Royal Society of London. 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