Catherine A. Toft

Principles for the Conservation of Wild Living Resources

We describe broadly applicable principles for the conservation of wild living resources and mechanisms for their implementation. These principles were engendered from three starting points. First, a set of principles for the conservation of wild living resources (Holt and Talbot 1978) required reexamination and updating. Second, those principles lacked mechanisms for implementation and consequently were not as effective as they might have been. Third, all conservation problems have scientific, economic, and social aspects, and although the mix may vary from problem to problem, all three aspects must be included in problem solving. We illustrate the derivation of, and amplify the meaning of, the principles, and discuss mechanisms for their implementation. The principles are: Principle I. Maintenance of healthy populations of wild living resources in perpetuity is inconsistent with unlimited growth of human consumption of and demand for those resources. Principle II. The goal of conservation should be to secure present and future options by maintaining biological diversity at genetic, species, population, and ecosystem levels; as a general rule neither the resource nor other components of the ecosystem should be perturbed beyond natural boundaries of variation. Principle III. Assessment of the possible ecological and sociological effects of resource use should precede both proposed use and proposed restriction or expansion of ongoing use of a resource. Principle IV. Regulation of the use of living resources must be based on understanding the structure and dynamics of the ecosystem of which the resource is a part and must take into account the ecological and sociological influences that directly and indirectly affect resource use. Principle V. The full range of knowledge and skills from the natural and social sciences must be brought to bear on conservation problems. Principle VI. Effective conservation requires understanding and taking account of the motives, interests, and values of all users and stakeholders, but not by simply averaging their positions. Principle VII. Effective conservation requires communication that is interactive, reciprocal, and continuous. Mechanisms for implementation of the principles are discussed.

Feeding Ecology of Thirteen Syntopic Species of Anurans in a Seasonal Tropical Environment

SummaryThirteen species of anurans belonging to three families forage diurnally for arthropods in the leaf litter of the lowland rainforest at the Río Llullapichis in Amazonian Perú. This paper investigates the diets and patterns of coexistence in this group of ecologically similar species. All thirteen species use the forest floor habitat without apparent differentiation. Most species take prey in proportions significantly different from those occurring in the leaf litter and comprise two specialist guilds: dendrobatids and bufonids that eat hard-bodied, slow-moving arthropods such as ants and mites; and leptodactylids that eat soft-bodied, mobile arthropods, primarily orthopterans and large spiders. Dendrobates femoralis (Boulenger) is a generalist, taking prey in proportions not significantly different from those in the leaf litter. Within specialist guilds, body sizes of species vary and are correlated with the size of prey taken. Foraging behavior and predator defense also correlate with the type and sizes of prey taken. Ant specialists tend to be poisonous and active searchers, taking many small prey per day. Non-ant specialists are cryptic, sit-and-wait foragers that take few large prey per day. Similarity in diet within guilds tends tobe lowest in the dry season when food is less abundant, suggesting that food is in short supply in the dry season.

Seasonal Variation in Populations of Panamanian Litter Frogs and Their Prey: A Comparison of Wetter and Drier Sites

SummaryVarious species of frogs and toads, belonging to the genera Bufo, Atelopus, Dendrobates, Colostethus, and Eleutherodactylus, occur in the leaf litter in rainforest in Panamá. This study compares the litter communities at two sites in Panamá: Pipeline Road, the drier site, and Carti Road, the wetter site. At both sites, frog abundance is greater in the dry season, when abundance of their prey, the litter arthropods, is greater. Species diversity does not change seasonally at either site; however, species diversity differs strikingly between sites, with Carti Road having the greater species diversity. Similarity in diet does not vary consistently with seasonal changes in food abundance at a single site or with differences in species diversity between sites. These results suggest that neither moisture nor food abundance alone influences the abundance or the diversity of litter frogs at these two sites in Panamá.

Diet specialization in small vertebrates: mite-eating in frogs

This study examines the morphological, taxonomic, ecological, and ontogenetic correlates of mite-eating (acariphagy) in anurans to increase our understanding of diet specialization in vertebrate insectivores . In a review of the literature (Part I), mites were abundant in terrestrial habitats at many locations worldwide, yet mites are not commonly reported as prey in anuran diets. In a detailed study of tropical ground-dwelling anurans (Part II), the diets of all species included mites

Spider populations: extraordinarily high densities on islands without top predators.

Distributions and densities of orb spiders on small islands are extremely variable. Species occurrences are far more irregular for spiders than vertebrates on the same islands. Much variation in spider density is explainable by distance from the presumed source of colonists and presence or absence of vertebrate predators. As has been predicted for passive dispersers, densities decline exponentially with distance. For a given distance, spider densities are about ten times greater on islands without vertebrate predators than on those with such predators.

A 10-year demographic study of rabbitbrush (Chrysothamnus nauseosus) : growth, survival and water limitation

A population of 126 adult rabbitbrush (Chrysothamnus nauseosus var. consimilis) was followed for 10 consecutive years from 1983 through 1992 in a sanddune ecosytem on the north shore of Mono Lake, California. The study area received an average (1981–1992) of 160 mm total annual precipitation of which 55 mm fell from April through October, making this site drier than other known sites in the Great Basin desert where C. nauseosus occurs. Cover of all shrubs was 18.0%, and that of C. nauseosus 7.5%, in the 3077 m2 study plot. Water was limiting for this population of C. nauseosus, exerting large effects on new canopy growth and reproductive effort in a given year, on survival, and on establishment of juveniles into the adult population. Growth and survivorship of the adult shrubs were significantly correlated with the depth to ground water, which varied from 3.6 to 6.0 m below the surface during the study, and not with any measure of precipitation in a given year or adjacent years. Shrubs in this population exhibited a net decrease in size between 1983 and 1992. The region experienced a significant drought from 1987 onwards, with some increase in precipitation after 1990. Mortality of shrubs began in 1987 and reached 22% by 1992. Individuals that died were smaller on average initially than individuals surviving throughout the study: 50% or more of the individuals having 4000 cm2 of canopy or less at the start of the study died by 1992. Elevation (m msl) of each shrub in the study area, presumably correlated with depth to ground water, had no effect on growth but a weak effect on survival during the study period. Specific microsite had significant effects, with shrubs on steep slopes being smaller, having more negative “growth” slopes, and being more likely to die during the drought compared to individuals occurring on flatter gradients. Recruiment of juveniles into the population did not occur after 1985. Competition between shrubs could not be definitively demonstrated during the study, but only indirect tests for competition were used. Adult C. nauseosus and adults of all species combined (Sarcobatus vermiculatus with 9.6% cover, Tetradymia tetrameres with 0.8% cover and Chrysothamnus viscidiflorus with 0.02% cover) were randomly distributed, failing to support the hypothesis of competition if competition for water results in a uniform distribution of shrubs. Moreover, comparison of the spatial dispersion of C. nauseosus individuals before (1985) and after (1992) mortality did not reveal competitive thinning toward uniformity. On the other hand, larger individuals were farther from their nearest neighbor than were smaller individuals, an effect postulated to result from competitive thinning.

Dispersion of a small-island population of the spider Metepeira datona (Araneae: Araneidae) in relation to web-site availability

SummaryMetepeira datona is the commonest orbweaving spider on very small islands of the central Bahamas. Where studied, large spiders built higher, wider and deeper webs than did small spiders, and they oriented webs modally so as to expose the least surface to the prevailing winds. About 17% of webs contained more than one spider, but large females almost never shared webs with one another. All individuals combined, and sex-age classes individually (including large females), were significantly more clumped in 2-dimensional space than random. Moreover, potential web sites for large females were about 10 x as common as occupied sites, were dispersed randomly, and were significantly less clumped than occupied sites. We conclude that a rudimentary coloniality exists and speculate on predator defense, prey capture, sharing of silk and structural support as adaptive functions.

Effect of Seed Size on Seedling Performance in a Long‐Lived Desert Perennial Shrub (Ericameria nauseosa: Asteraceae)

We investigated how seed size and timing of emergence interact with environmental conditions to determine seedling performance in one population of the long‐lived perennial shrub Ericameria nauseosa var. oreophila (Asteraceae) in the sand dune ecosystem near Mono Lake, California. Size of seeds varied significantly among and within individual plants, and this variation had important consequences for size, growth, and survival of seedlings in both greenhouse and field experiments. Larger‐seeded seedlings had greater biomass, greater percentage of total plant biomass allocated to roots, and longer taproots than seedlings from smaller seeds. Seedlings grown in native soil had less total biomass than seedlings grown in augmented soil but greater allocation of biomass to roots. In a field experiment following individually weighed seeds, seedlings emerging from larger seeds germinated and emerged earlier and at a higher rate than did smaller‐seeded seedlings. Larger‐seeded seedlings were larger at emergence, remained larger through time, and lived longer than smaller‐seeded seedlings. In all stages of early seedling establishment, from germination through the first summer drought, and by all criteria, larger‐seeded seedlings performed better than smaller‐seeded seedlings. Given the considerable longevity of adults and the extremely small size of the wind‐dispersed seeds, these aspects of seed and seedling performance have a remarkably significant impact on the survival and reproduction of subsequent life stages of E. nauseosa at this site.

SPATIAL DISPERSION AND DENSITY DEPENDENCE IN A PERENNIAL DESERT SHRUB (CHRYSOTHAMNUS NAUSEOSUS: ASTERACEAE)

Dogma asserts that desert shrubs should become uniformly dispersed through time through a process of self-thinning caused by competition for water. We present long-term data (1985–2001) on two nearby populations of the perennial shrub, Chrysothamnus nauseosus ssp. consimilis, in sand-dune ecosystems near Mono Lake, California. Because previous studies established that water limited the growth, survival, and reproduction of this shrub, we searched for population-level patterns of competition. A seven-year history of survival, growth, and flowering of marked individuals delineated five demographic stage classes corresponding roughly to age and plant size: seedlings, nonflowering juveniles, juveniles that later flowered, adults that flowered intermittently, and “immortal” adults that flowered annually. For all stages except nonflowering juveniles, initial size was a strong predictor of life expectancy, and for the reproductive classes, flowering was associated with larger size and higher survival. Survival o...

Parrots Eat Nutritious Foods despite Toxins

Background Generalist herbivores are challenged not only by the low nitrogen and high indigestibility of their plant foods, but also by physical and chemical defenses of plants. This study investigated the foods of wild parrots in the Peruvian Amazon and asked whether these foods contain dietary components that are limiting for generalist herbivores (protein, lipids, minerals) and in what quantity; whether parrots chose foods based on nutrient content; and whether parrots avoid plants that are chemically defended. Methodology/Principal Findings We made 224 field observations of free-ranging parrots of 17 species in 8 genera foraging on 102 species of trees in an undisturbed tropical rainforest, in two dry seasons (July-August 1992–1993) and one wet season (January-February1994). We performed laboratory analyses of parts of plants eaten and not eaten by parrots and brine shrimp assays of toxicity as a proxy for vertebrates. Parrots ate seeds, fruits, flowers, leaves, bark, and insect larvae, but up to 70% of their diet comprised seeds of many species of tropical trees, in various stages of ripeness. Plant parts eaten by parrots were rich in protein, lipid, and essential minerals, as well as potentially toxic chemicals. Seeds were higher than other plant materials in protein and lipid and lower in fiber. Large macaws of three species ate foods higher in protein and lipids and lower in fiber compared to plant parts available but not eaten. Macaws ate foods that were lower in phenolic compounds than foods they avoided. Nevertheless, foods eaten by macaws contained measurable levels of toxicity. Macaws did not appear to make dietary selections based on mineral content. Conclusions/Significance Parrots represent a remarkable example of a generalist herbivore that consumes seeds destructively despite plant chemical defenses. With the ability to eat toxic foods, rainforest-dwelling parrots exploited a diversity of nutritious foods, even in the dry season when food was scarce for other frugivores and granivores.