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Herbivore attack is widely known to reduce food quality and to increase chemical defenses and other traits responsible for herbivore resistance. Inducible defenses are commonly thought to allow plants to forgo the costs of defense when not needed; however, neither their defensive function (increasing a plant's fitness) nor their cost-savings function have been demonstrated in nature. The root-produced toxin nicotine increases after herbivore attack in the native, postfire annual Nicotiana attenuata and is internally activated by the wound hormone, jasmonic acid. I treated the roots of plants with the methyl ester of this hormone (MeJA) to elicit a response in one member of each of 745 matched pairs of plants growing in native populations with different probabilities of attack from herbivores, and measured the lifetime production of viable seed. In populations with intermediate rates of attack, induced plants were attacked less often by herbivores and survived to produce more seed than did their uninduced counterparts. Previous induction did not significantly increase the fitness of plants suffering high rates of attack. However, if plants had not been attacked, induced plants produced less seed than did their uninduced counterparts. Jasmonate-induced responses function as defenses but are costly, and inducibility allows this species to forgo these costs when the defenses are unnecessary

Squirrel Nation is a history of Britain's two species of squirrel over the past two hundred years. The red squirrel, although rare, is among the most cherished of native species. Grey squirrels, by contrast, are one of the most frequently seen wild creatures in our gardens, parks, towns and countryside, and many Britons consider it to be a foreign interloper, introduced from North America in the late nineteenth century. By examining this animal's colonization of Britain, Peter Coates also explores timely issues of belonging, nationalism, citizenship and the defence of borders within Britain today. Ultimately, though people are swift to draw distinctions between British squirrels and squirrels in Britain, Squirrel Nation shows that Britain's two squirrel species have much more in common than at first appears.

We examined the relationship between body size and perceptual range (the distance at which an animal can perceive landscape elements) for a group of forest-dwelling rodents. We used previously published data on orientation ability at various distances for three sciurid species (gray squirrel, fox squirrel and chipmunk) and one murid species (white-footed mouse) to build a predictive model. We found a significant positive relationship between perceptual range and body mass. Although this model was built using a 15.5 m high horizon, we used this relation to predict the perceptual range of root voles (3.9-4.3 m) orienting towards a 0.5 m high horizon which was consistent with other empirical work suggesting a value of something less than 5 m. This model illustrates a relationship between perceptual range and body size and can be used to develop starting points for future investigations of perceptual range for similar organisms.

By immunizing prion knockout mice (Prnp-/-) with recombinant murine prion protein (PrP(c)), we obtained a panel of mAbs specific for murine PrP(c). These mAbs can be applied to immunoblotting, cell surface immunofluorescent staining, and immunohistochemistry at light and electron microscopy. These mAbs recognize both the normal (PrP(c)) and protease-resistant (PrP(res)) isoforms of PrP. Some mAbs are species restricted, while others react with PrP from a broad range of mammals including mice, humans, monkeys, cows, sheep, squirrels, and hamsters. Moreover, some of the mAbs selectively recognize different PrP glycoforms as well as the metabolic fragments of PrP(C). These newly generated PrP(C) antibodies will help to explore the biology of PrP(c) and to establish the diagnosis of prion diseases in both humans and animals

Our approach is twofold. First, with 1964-1983 data on red squirrel (Sciurus vulgaris) in 11 provinces in Finland we show that population fluctuations in different parts of the country are largely synchronous. Second, using two differing model types for producing the dynamics of populations we set up to examine the synchronizing effect of an extrinsic disturbing factor, the Moran effect. We show that in a spatially structured population system a randomly occurring stochastic perturbation reducing reproduction success is indeed capable of synchronizing subpopulations. The synchronizing effect is achievable with a wide range of probabilities of occurrence and strengths. However, when the Moran effect occurs in most years its synchronizing power wanes, despite the strength of the effect. Allowing regionality in the variance of the strength of the Moran effect reduces the synchronizing capacity of the perturbation. The Moran effect is also capable of producing a wide range of population dynamics from very simple premises.

In a single population of Ipomopsis arizonica (Polemoniaceae), we show a continuum of compensatory responses to vertebrate herbivory. We demonstrate experimentally that the degree of herbivore impact depends on plant association, nutrient availability, and timing of grazing. From 1985 to 1987, the most common response to vertebrate herbivory was equal compensation, whereby grazed plants set numbers of fruits and seeds equal to controls within the same growing season. However, we also observed cases of significant overcompensation and undercompensation. In 1985 and 1987, overcompensation occurred in vertebrate-grazed plants that were supplemented with nutrients and growing free of competition. These plants produced 33% to 120% more fruit than control, ungrazed plants. Cases of undercompensation occurred in groups where I. arizonica grew in association with grasses or where nutrients were not supplemented. Grazed and clipped plants in these groups produced from 28% to 82% as many fruits as did ungrazed controls. Our studies indicate that the compensatory response of plants to grazing is probabilistic when three external factors are considered. The probability of compensation for herbivory decreases as competition with other plants increases, as nutrient levels decrease, and as the timing of herbivory comes later in the growing season.

Models of community organization involve variations of the top-down (predator control) or bottom-up (nutrient limitation) hypotheses. Verbal models, however, can be interpreted in different ways leading to confusion. Therefore, we predict from first principles the range of possible trophic level interactions, and define mathematically the instantaneous effects of experimental perturbations. Some of these interactions are logically and biologically unfeasible. The remaining set of 27 feasible models is based on an initial assumption, for simplicity, of linear interactions between trophic levels. Many more complex and non-linear models are logically feasible but, for parsimony, simple ones are tested first. We use an experiment in the boreal forest of Canada to test predictions of instantaneous changes to trophic levels and distinguish between competing models. Seven different perturbations systematically removed each trophic level or, for some levels, supplemented them. The predictions resulting from the perturbations were concerned with the direction of change in biomass in the other levels. The direct effects of each perturbation produced strong top-down and bottom-up changes in biomass. At both the vegetation and herbivore levels top-down was stronger than bottom-up despite some compensatory growth stimulated by herbivory. The combination of experiments produced results consistent with two-way (reciprocal) interactions at each level. Indirect effects on one or two levels removed from the perturbation were either very weak or undetectable. Top-down effects were strong when direct but attenuated quickly. Bottom-up effects were less strong but persisted as indirect effects to higher levels. Although the 'pure reciprocal' model best fits our results for the boreal forest system different models may apply to different ecosystems around the world.

Seed fate pathways were investigated for antelope bitterbrush (Purshia tridentata), a common and economically important shrub, from all 1988 to fall 1992 at the Whittell Forest and Wildlife Area in Little Valley, Washoe County, on the east slope of the Sierra Nevada in western Nevada. Rodents harvested bitterbrush seeds from late July to September, taking them either directly off the fruiting twigs or picking up fallen fruits from the ground surface and carrying from 63 to 80% of the seeds away intact from shrubs. Radioactively labelled bitterbrush seeds placed under four source shrubs were removed and scatter hoarded primarily by yellow pine chipmunks (Tamias ameonus). Caches contained a mean of 4-11 seeds and were located within 25 m from the source shrubs. Cache depth and microhabitat selection were generally favorable for bitterbrush seedling establishment. Chipmunks and other rodents found many of the seed caches and either ate the seeds (53%) or reached them elsewhere. Chipmunks probably also carried some intact seeds to larders in hibernacula to use as a winter food source. In spring, >99% of emerging seedlings occurred in clumps containing from 2 to 104 individuals. An estimated 5.3 and 8.5% of those seeds cached by rodents and 1.1 and 2.4% of the seeds produced by shrubs in 1990 and 1991 produced emergent seedlings the following spring. Seedling mortality rates during their 1st yr ranged from 78 to 92%. Grazing by rodents was the most important source of mortality during early spring, and most seedling deaths were caused by desiccation during summer. Despite considerable attrition of individuals within clumps, most mature @'shrubs@' consisted of two or more individuals. The seed fate pathway that resulted in the highest probability of seedling establishment at this study site was harvest, dispersal, and scatter hoarding by chipmunks, and subsequent neglect of those caches. Retrieval of cached seeds by chipmunks followed by redistribution of those seeds to neglected secondary caches also resulted in many seedlings. Modes of seed dispersal based solely on abiotic agents appear to be insufficient to account for significant recruitment of bitterbrush seedlings.

Individual variation in lifetime reproductive success (number of weaned offspring in a lifetime) of female red squirrels was studied in two populations in North Belgium for 8 yr. Fitness, the number of reproducing offspring, was calculated combining expected survival to reproductive age of dispersing young and reproductive performance of local recruits. Of 66 resident females, 20 (30%) never produced young. 89% of territorial females had offspring, while all non-territorial females failed to reproduce. Lifetime reproductive success of mothers (females that produced at least one weaned young) averaged 5.04 young (range 1-11), fitness averaged 2.07 (range 0.26-4.44). Both measures of reproductive success were strongly correlated ( R2=0.73). Variation in fitness and lifetime reproductive success was mainly the consequence of variation in the number of litters produced. Variation in body condition, foot length (size) and territory quality explained 50% of variation in the number of litters. Variation in the number of young/litter, age at first breeding and year of birth were not significantly correlated with variation in lifetime reproductive success. We conclude that large, heavy females that established home ranges in food-rich areas live longer and produce more young than lighter, shorter-lived females living in poorer territories, and discuss the occurrence of chance-events affecting reproductive output in young and old squirrels.

We combine the two classical questions of foraging theory, patch use and diet choice, to show how an animal's diet may be the predictable product of simple foraging strategies in response to the distribution and abundance of its foods. We consider four reasons why a forager may exhibit a partially selective diet. First, different foods may co-occur within the same patch and the forager may have different encounter probabilities on different food types. Second, different foods may co-occur within the same patch and the forager may reject an encountered food item based upon its type. Third, different foods may be distributed within distinct patches and the forager's use of a patch may be influenced by joint considerations of food type and abundance. Fourth, different foods may occur in distinct habitats and the forager may allot time among habitats for reasons other than food type. To test these predictions, we measured the giving-up densities of free-living fox squirrels in experimental food patches containing peanut and/or sunflower seeds. When foods co-occur, the squirrels are partially selective on sunflower at high quitting harvest rates, and, at low quitting harvest rates, they are partially selective on peanuts. This switch in selectivity suggests that sunflower are preferred to peanut, and that squirrels have a higher encounter probability on peanut than sunflower. When foods occur in different patches, squirrels are partially selective on whichever food has the relatively higher initial abundance. In response to predation risk, squirrels forage food patches more thoroughly near cover than away from cover. As a result, if peanut and sunflower occur in different habitats, fox squirrel are partially selective on whichever food occurs in the safer habitat.