Predation Index Research Articles

Circumstances Associated with Predation Rates on Sheep and Goats

Factors possibly associated with high (over 5%) and low (0-5%) predation intensities were compared among 95 sheep or goat producers in 5 states to determine if important differences were evident between the 2 groups. Data were compared for the following variables: losses to predation, flock size, type of ranch operation, management practices, predator indices, prey indices, use of U.S. Animal Damage Control program, private control efforts, predation history, timing of predation, and presence of other sheep or goats nearby. Overall, 45% of the producers reported over 5% predation losses of their lambs or kids and predation percentages tended to increase with decreased flock sizes. Feeder lamb and range sheep operations had predominantly low predation loss percentages, but most operations that included goats reported over 5% predation losses due to goat predation. A variety of management practices were used by both groups; however, low loss producers indicated low natural prey and predator populations. Most of the producers used the federal ADC program and some type of private control effort, although more high loss producers used both types. Rough, bottom, and brush grazing lands, historic predation problems, and high predator indices characterized many of the high loss producers. Predation intensity on livestock among producers is variable (Gee et al. 1977, Nass 1980). Various studies (deCalesta 1978, Schaefer et al. 1981, and others) have shown that livestock losses to predators vary significantly among samples of producers; however, data on reasons for this variability are lacking (Gee et al. 1977). Frequently, experienced animal damage control personnel know or suspect why specific levels of predation are occurring at specific times, but there have been no standardized mechanisms for recording, tabulating, and comparing the information on a ranchby-ranch basis. Boggess et al. 1980, Meduna 1977, and Schaefer et al. 1981 have explored the effects of some husbandry practices on livestock predation levels. The objective of our study was to identify factors common to ranches with high sheep or goat predation and compare them with low predation loss ranches.

The Relationships between Beech (Nothofagus Sp.) Seedfall and Populations of Mice (Mus musculus), and the Demographic and Dietary Responses of Stoats (Mustela erminea), in Three New Zealand Forests

SUMMARY (1) There was a significant relationship between seedfall and populations of mice in all forests studied. Good seedfalls were followed by increases in density of mice and changes in population structure not seen in years when the seedfall failed. Predictability of these changes decreased with increasing diversity of forest composition. (2) Stoats responded both numerically and functionally to increases in mice. There was a significant relationship between the densities of mice and of stoats in summer in two forests. (In a third, this relationship was modified by the presence nearby of many lagomorphs, an important alternative prey for stoats.) The numerical response was due to increased survival, in the uterus or the nest, of young stoats born in spring when mice were abundant, not to increased fecundity of adult female stoats. In all three forests, stoats ate significantly more mice in the summers that mice were abundant. (3) Ship rats (Rattus rattus (L.)) were most abundant in the most diverse of the three forests. The density index for R. rattus increased there after the 1976 seedfall, but not after that of 1979. A few kiore (R. exulans (Peale)) coexisted with R. rattus in this forest. (4) Stoats did not eat significantly fewer birds when there were plenty of mice, either in summer or autumn, but nevertheless there was a significant negative correlation between the proportions of birds and mice in the diet in autumn. In summer this correlation was very weak and probably non-existent. (5) A 'bird predation index', which takes into account both the numbers of stoats present and what they ate, suggests that more birds are eaten in summers of peak numbers of mice and stoats, because of the strong numerical response by stoats to mice and lack of 'buffering' of birds by mice. In autumn this effect is weakened by a regular seasonal switch by stoats from birds to mice, especially in the autumn of a mouse peak year. (6) The indirect effects of mouse irruptions on populations of forest birds in New Zealand should be further examined. Control of stoats in mouse peak summers could prevent a temporary increase in predation on birds by stoats during the highest risk period, though whether this would benefit the birds is unknown.

Predator—prey (Vole—Cricket) interactions: The effects of wood preservatives

AbstractThe rate of loss of crickets (Acheta domestica L.), with and without the presence of an adventitious predator, the gray‐tailed vole (Microtus canicaudus), has been studied in Terrestrial Microcosm Chambers (TMC‐II) treated with pine stakes impregnated with creosote, bis(tri‐n‐butyltin)oxide (TBTO), dieldrin (HEOD), pentachlorophenol (PCP) or a toluene solvent control. The first‐order rate of cricket loss (‐k) increased only for HEOD, to a maximum at 33 d post‐treatment, with oscillations of about a 16‐d period. This result infers a “cricket‐available” compartment of HEOD and/or metabolites with concentrations that must be greater than those measured in air, soil, water or plants and other biota. When a gravid vole was subsequently added to each TMC, the predation index (Δkv) increased for control and PCP, but declined markedly for creosote and HEOD, and to a lesser extent for TBTO.

Aphid Feeding by Some Polyphagous Predators in Relation to Aphid Density in Cereal Fields

(1) Samples of aphids and predators were taken from ten spring barley and winter wheat fields between May and September 1972-77. (2) The guts of c. 12 000 predators were dissected and the presence or absence of aphid remains recorded. Sixteen species of Carabidae, three species of Staphylinidae and one species of earwig were shown to have fed on aphids. (3) No overall relationship was found between the amount of feeding and aphid densities in the different years. But, when the species were considered separately, it was found that the proportion containing aphid remains increased with aphid density, though the form of this relationship varied between species. (4) Tachyporus spp. had a limited response to aphid density and Amara plebeja, A. aenea and Notiophilus biguttatus ate aphids only at higher aphid densities. Forficula auricularia, Agonum dorsale and Demetrias atricapillus were the most important, both in terms of the overall percentage containing aphid remains, and the predation index (proportion containing aphid remains during the aphid increase phase multiplied by the mean density of the predator at this time). These three species should be the most valuable in restricting build up of aphids. (5) Successful aphid predation at low aphid density may be partly related to the climbing ability of the predator.

Interactive effects of predation pressure and insecticide (temefos) toxicity on populations of the marsh fiddler crab Uca pugnax

The interaction of predation pressure with lethal and sublethal effects of temefos (Abate®) an organophosphorous insecticide, were studied in field populations of Uca pugnax (S.I. Smith). Changes in fiddler crab population densities were followed in open-marsh temefos-treated and untreated test plots and in treated and untreated plots which were caged over to reduce predation by marsh birds. Temefos significantly reduced the population density of U. pugnax in the open test plots but not in the caged plots. These results indicate that temefos has a primarily sublethal effect on the crabs, the effect becoming lethal only after interaction with avian predation. Evidence from the presence of a time-lag effect in the population decrease, from a calculated predation index, and from laboratory studies reported elsewhere of behavioral alteration by temefos also supports the conclusion that temefos primarily impairs the escape response of U. pugnax: this leads to increased predation and subsequently to a decreased fiddler crab population. Such studies of sublethal effects of toxicants and field studies of interactions of lethal and sublethal effects of such compounds with natural population dynamics of affected species are necessary to evaluate possible effects of toxicants on populations.