scholarly journals What Explains Forest Grouse Mortality: Predation Impacts of Raptors, Vole Abundance, or Weather Conditions?

2012 ◽  
Vol 2012 ◽  
pp. 1-10 ◽  
Author(s):  
Risto Tornberg ◽  
Vitali Reif ◽  
Erkki Korpimäki
Keyword(s):  
Linear Response ◽  
Weather Conditions ◽  
Generalist Predators ◽  
Black Grouse ◽  
Main Prey ◽  
Density Dependent ◽  
Survival Pattern ◽  
Kill Rate ◽  
Specialist Predators ◽  
Predation Rates

We investigated predation rates of black grouse chicks during 1985–2007 in two localities in western Finland in light of three predation hypothesis: The Alternative Prey Hypothesis (APH) stating that vole-eating generalist predators cause a collapse in grouse reproduction after voles’ decline, the Main Prey Hypothesis (MPH), where grouse specialised predators by a lagged response cause an inversely density dependent predation for prey and the Predation Facilitation Hypothesis (PFH), where generalist and specialist predators act in concert. We also studied the effect of weather on grouse reproduction. We found that buzzard predation alone did not support APH, but did so when combined with goshawk predation. Kill rate by goshawks showed a linear response for black grouse chicks but was not density dependent. It, however, explained the losses of chicks but not their autumn density. Combined density of chicks with adults correlated with vole index in the latter study period (since 1994), thus, giving some support for APH. Weather seemed to have no effect on black grouse reproduction. Although buzzards and goshawks took, on average, only 10% of hatched grouse chicks we conclude that the among-year survival pattern of juvenile forest grouse may largely be determined by raptor predation.

scholarly journals Effects of Temporal Crop β Diversification of a Cereal-Based Cropping System on Generalist Predators and Their Biocontrol Potential

2021 ◽  
Vol 3 ◽  
Author(s):  
Giovanni Antonio Puliga ◽  
Jan Thiele ◽  
Hauke Ahnemann ◽  
Jens Dauber
Keyword(s):  
Crop Rotation ◽  
Pest Control ◽  
Cover Crops ◽  
Cropping Systems ◽  
Cropping System ◽  
Generalist Predators ◽  
Activity Density ◽  
Biocontrol Potential ◽  
Natural Pest Control ◽  
Predation Rates

In agroecosystems, crop diversification plays a fundamental role in maintaining and regenerating biodiversity and ecosystem services, such as natural pest control. Temporal diversification of cropping systems can affect the presence and activity of natural enemies by providing alternative hosts and prey, food, and refuges for overwintering. However, we still lack studies on the effects of temporal diversification on generalist predators and their biocontrol potential conducted at field scale in commercial agricultural settings. Here, we measured proxies of ecosystem functions related with biological pest control in 29 commercial agricultural fields characterized by cereal-based cropping system in Lower-Saxony, northern Germany. The fields differed in the number of crops and cover crops cultivated during the previous 12 years. Using the Rapid Ecosystem Function Assessment approach, we measured invertebrate predation, seed predation and activity density of generalist predators. We aimed at testing whether the differences in the crop rotations from the previous years would affect activity of predators and their predation rates in the current growing season. We found that the length of the crop rotation had neutral effects on the proxies measured. Furthermore, predation rates were generally lower if the rotation comprised a higher number of cover crops compared to rotation with less cover crops. The activity density of respective taxa of predatory arthropods responded differently to the number of cover crops in the crop rotation. Our results suggest that temporal crop diversity may not benefit the activity and efficiency of generalist predators when diversification strategies involve crops of very similar functional traits. Adding different resources and traits to the agroecosystems through a wider range of cultivated crops and the integration of semi-natural habitats are aspects that need to be considered when developing more diverse cropping systems aiming to provide a more efficient natural pest control.

Termitivore or detritivore? A quantitative investigation into the diet of the East African caecilian Boulengerula taitanus (Amphibia: Gymnophiona: Caeciliidae)

2004 ◽  
Vol 54 (1) ◽  
pp. 45-56 ◽  
Author(s):  
G. John Measey ◽  
Olivier Gaborieau
Keyword(s):  
Organic Matter ◽  
Stomach Contents ◽  
Gut Contents ◽  
Generalist Predators ◽  
East African ◽  
Quantitative Investigation ◽  
Soil Macrofauna ◽  
Taita Hills ◽  
Specialist Predators ◽  
African Genus

AbstractMost caecilians are thought to be generalist predators of soil ecosystem engineers (earthworms, termites and ants), but it has been suggested that members of the East African genus Boulengerula are specialist predators. Surprisingly, in the only detailed study of diet of any Boulengerula, the authors speculated that B. taitanus is partly detritivorous, based on the large amount of organic matter found in the alimentary canal. Here we test the conflicting hypotheses that B.taitanus is a termitivore or detritivore, using the stomach and gut contents of 47 specimens collected in the Taita Hills, Kenya. Termites and earthworms contribute most significantly to diet by number and mass, respectively. These constitute the major dietary items, together with dipteran larvae and other soil macrofauna. Contents of the intestine are mostly soil and organic matter originating from prey items. The mass content of the intestines averages 69% of total gut contents, and is significantly greater than identifiable stomach contents. The null hypotheses that B. taitanus is a generalist and a predator are not rejected.

Specialist Predators, Generalist Predators, and the Microtine Rodent Cycle

10.2307/5465 ◽  
1991 ◽  
Vol 60 (1) ◽  
pp. 353 ◽  
Author(s):  
Ilkka Hanski ◽  
Lennart Hansson ◽  
Heikki Henttonen
Keyword(s):  
Generalist Predators ◽  
Microtine Rodent ◽  
Specialist Predators

Unstable predator–prey dynamics permits the coexistence of generalist and specialist predators, and the maintenance of partial preferences

2013 ◽  
Vol 59 (1) ◽  
pp. 27-36 ◽  
Author(s):  
Robert D. Holt ◽  
Manojit Roy ◽  
Michael Barfield
Keyword(s):  
Dynamic Instability ◽  
Poor Quality ◽  
Generalist Predators ◽  
Functional Responses ◽  
High Quality ◽  
Dietary Specialization ◽  
Predator Prey ◽  
Predator Prey Model ◽  
Partial Preference ◽  
Specialist Predators

Saturating functional responses are a unifying principle in ecology, influencing processes at organizational levels from dietary specialization in individuals, to population instability, to community-level indirect interactions among alternative prey. These effects are interrelated. We explore a predator–prey model and demonstrate that unstable dynamics promote coexistence of specialist and generalist predators, when the specialist attacks only high-quality prey, and the generalist attacks high- and low-quality prey (that alone cannot maintain the predator). Coexisting specialist and generalist predators are vulnerable to invasion and replacement by predators with fixed partial preferences. The evolutionarily stable partial preference increases with increasing dynamic instability, but typically declines with increasing abundance of the low-quality prey. Coexisting specialist and generalist consumers, or partial preferences, typically reduce the potential for poor-quality prey to indirectly benefit high-quality prey. We suggest that dynamic instability may also contribute to the evolutionary maintenance of seemingly maladaptive oviposition choices by insect parasitoids.

The functional response and prey preference of generalist Nabis (Hemiptera: Nabidae) predators to leafhopper prey (Hemiptera: Cicadellidae)

2018 ◽  
Vol 150 (2) ◽  
pp. 190-200 ◽  
Author(s):  
David J. Stasek ◽  
James N. Radl ◽  
Thomas O. Crist
Keyword(s):  
Functional Response ◽  
Trifolium Pratense ◽  
Red Clover ◽  
Prey Preference ◽  
Generalist Predators ◽  
Forage Crops ◽  
Forage Crop ◽  
Survival Probabilities ◽  
The Family ◽  
Predation Rates

AbstractInsects of the family Nabidae (Hemiptera) are generalist predators commonly found in agroecosystems, but little is known about their predation rates on common pests of forage crops. We determined the functional response and prey preference of Nabis Latreille species to two common leafhopper pests of red clover (Trifolium pratense Linnaeus; Fabaceae): Agallia constricta Van Duzee (Hemiptera: Cicadellidae) and Ceratagallia agricola (Hamilton) (Hemiptera: Cicadellidae). We also determined the survivorship of A. constricta to predation by Nabis species over the course of five days. The Nabis species displayed a Type III functional response to both leafhopper species with a preference for A. constricta. The 10-A. constricta/cage treatments and 20-A. constricta/cage treatments had the highest survival probabilities after five days with survival probabilities of 0.19 and 0.23, respectively. These results indicate that Nabis species may help in controlling leafhopper populations in forage-crop systems.

scholarly journals Weather, cultivar and density-dependent processes influence on aphid in alfalfa

Bragantia ◽  
2007 ◽  
Vol 66 (2) ◽  
pp. 285-290 ◽  
Author(s):  
Alexandre de Almeida e Silva ◽  
Elenice Mouro Varanda ◽  
Joaquim Bartolomeu Rassini
Keyword(s):  
Crop Production ◽  
Weather Conditions ◽  
Climatic Conditions ◽  
Population Variation ◽  
Density Dependent ◽  
Insect Density ◽  
Maximum Temperatures ◽  
One Year ◽  
Dependent Processes

It is important to understand the effects of weather, insect density and plant cultivar on insect abundance to predict and prevent crop production loss. The present work investigated the influence of such factors on aphid in alfalfa during one year (short term). Data was collected from September/1997 to August/1998 at Canchin Farm (CCPSE-EMBRAPA), São Carlos, State of São Paulo, Brazil. Weather conditions had, in general, little effect on the variation of aphid populations, but Therioaphis maculata abundance was negatively correlated to humidity. Moreover, high maximum temperatures and low levels of rainfall possible favored T. maculata high abundance on Crioula and P3 cultivars. Therefore, appropriate management of this species is required during hot and dry periods. Population variation of Acyrthosiphon spp., T. maculata and Aphis craccivora seems to be regulated by density dependent processes. Resistant cultivar CUF 101 had a lower abundance of T. maculata and A. craccivora and a narrower population variation than the other cultivars and may reduce their abundance on field. Long-term studies on population dynamics including the effect of climatic conditions and density-dependent factors on plant quality will contribute to pest management in alfalfa fields.

scholarly journals Pushed beyond the brink: Allee effects, environmental stochasticity, and extinction

2014 ◽  
Author(s):  
Gregory Roth ◽  
Sebastian Schreiber
Keyword(s):  
High Probability ◽  
Geometric Mean ◽  
Environmental Stochasticity ◽  
Initial Population ◽  
Positive Density ◽  
Allee Effects ◽  
Population Densities ◽  
Density Dependent ◽  
Environmental Fluctuations ◽  
Predation Rates

To understand the interplay between environmental stochasticity and Allee effects, we analyze persistence, asymptotic extinction, and conditional persistence for stochastic difference equations. Our analysis reveals that persistence requires that the geometric mean of fitness at low densities is greater than one. When this geometric mean is less than one, asymptotic extinction occurs with high probability for low initial population densities. Additionally, if the population only experiences positive density-dependent feedbacks, conditional persistence occurs provided the geometric mean of fitness at high population densities is greater than one. However, if the population experiences both positive and negative density-dependent feedbacks, conditional persistence only occurs if environmental fluctuations are sufficiently small. We illustrate counter-intuitively that environmental fluctuations can increase the probability of persistence when populations are initially at low densities, and can cause asymptotic extinction of populations experiencing intermediate predation rates despite conditional persistence occurring at higher predation rates.

scholarly journals Geographical variation in the spatial synchrony of a forest-defoliating insect: isolation of environmental and spatial drivers

2013 ◽  
Vol 280 (1753) ◽  
pp. 20122373 ◽  
Author(s):  
Kyle J. Haynes ◽  
Ottar N. Bjørnstad ◽  
Andrew J. Allstadt ◽  
Andrew M. Liebhold
Keyword(s):  
Gypsy Moth ◽  
Forest Type ◽  
Weather Conditions ◽  
Spatial Proximity ◽  
Generalist Predators ◽  
Population Fluctuations ◽  
Spatial Synchrony ◽  
Acorn Production ◽  
Environmental Perturbations ◽  
Underlying Mechanisms

Despite the pervasiveness of spatial synchrony of population fluctuations in virtually every taxon, it remains difficult to disentangle its underlying mechanisms, such as environmental perturbations and dispersal. We used multiple regression of distance matrices (MRMs) to statistically partition the importance of several factors potentially synchronizing the dynamics of the gypsy moth, an invasive species in North America, exhibiting outbreaks that are partially synchronized over long distances (approx. 900 km). The factors considered in the MRM were synchrony in weather conditions, spatial proximity and forest-type similarity. We found that the most likely driver of outbreak synchrony is synchronous precipitation. Proximity played no apparent role in influencing outbreak synchrony after accounting for precipitation, suggesting dispersal does not drive outbreak synchrony. Because a previous modelling study indicated weather might indirectly synchronize outbreaks through synchronization of oak masting and generalist predators that feed upon acorns, we also examined the influence of weather and proximity on synchrony of acorn production. As we found for outbreak synchrony, synchrony in oak masting increased with synchrony in precipitation, though it also increased with proximity. We conclude that precipitation could synchronize gypsy moth populations directly, as in a Moran effect, or indirectly, through effects on oak masting, generalist predators or diseases.

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