In a tropical cloud forest at Monteverde, Costa Rica, three understory shrub species overlap greatly in flowering seasons and share hummingbird pollinators (Lampornis calolaema). We conducted two field experiments to determine if a plant's pollination and subsequent reproductive output reflect local densities of conspecific and heterospecific flowers. We controlled floral composition in the neighborhoods surrounding 12 focal plants of self-compatible Besleria triflora (Gesneriaceae) and of self-incompatible Palicourea lasiorrachis (Rubiaceae), producing prescribed mixtures of flowers of the focal plants' conspecifics and of Cephaelis elata (Rubiaceae). Each experiment subjected each focal plant to four different treatments: a floral neighborhood of 10 conspecific flowers and 10 of Cephaelis within a radius of 20 m (Treatment A); 90:10 (B); 10:90 (C); and 50:50 (D). Focal plants themselves always had 10 open flowers. We assigned the sequence of treatments to each focal plant in a Latin square crossover design using three balanced blocks of four plants each. Dependent variables were: frequency of hummingbird probes per flower; pollen tubes in styles; and seed output per flower. From standard models of competition for pollination, we predicted that pollination levels and seed production would be ranked among treatments: B(90:10) > D(50:50) > A(10:10) > C(10:90). These overall predictions were supported for both Palicourea and Besleria, based on tests for directionality showing that the rank order among adjusted treatment means did not differ from the order predicted. Separate a priori treatment contrasts indicated that in both species increasing flower density above base levels (Treatment A, 10:10) by adding conspecific flowers alone (B, 90:10) or along with Cephaelis (D, 50:50) increased the rate at which hummingbirds visited focal plants' flowers. In Palicourea, both the number of pollen tubes in styles and seed output per flower increased in the same fashion. In Besleria, the only effect was increased pollination (but not seed output) from A (10:10) to B (90:10). In contrast, enriching the basic neighborhood (A, 10:10) with Cephaelis flowers (C, 10:90) did not alter frequencies of hummingbird probes to either species of focal plant. Heterospecific enrichment did, however, decrease both pollination levels and seed output in Palicourea, and seed output in Besleria. In general, altering the floral neighborhood affected Palicourea more strongly than Besleria. Apparently the intensity of density dependence, at least in terms of female reproductive success, varies among plant species sharing pollinators. Seed outputs in self-incompatible plants such as Palicourea may closely reflect flower densities of neighbors, but interspecific effects on fertilization in self-compatible plants such as Besleria may be density vague.

We investigated the impacts of various logging practices on habitat choice by the endemic Florida scrub lizard (Sceloporus woodi) in the Florida scrub of Ocala National Forest (ONF). We used large outdoor mesocosms as a novel means to evaluate lizard preferences for habitats with different structural features produced by standard forestry practices. Captive lizards were offered a choice between two adjoin- ing habitats (= sides of a mesocosm) created using one of two substratum treatments (SAND = 75% open sand; WOOD = 75% coarse woody debris (CWD)) coupled with one of two insolation treatments (LIGHT = ambient sunlight; DARK = 45% ambient sunlight). The mesocosms proved to be an effective technique for evaluating lizard habitat preferences. Lizards were easily observed and remained active and healthy throughout the experiment Sighting frequencies differed significantly among the four mesocosm sides, yielding an overall preference ranking of DARK SAND > LIGHT SAND > DARK WOOD - LIGHT WOOD. Analysis of sighting frequencies by treatment factors (substratum and insolation) and of dissimilarity ma- trices both indicated that habitat choice was based primarily on substratum composition and only weakly determined by insolation level. In addition, size- and gender-specific preferences suggest that social inter- actions may help shape patterns of habitat used in conjunction with individual preferences. We conclude that the least favored mesocosm side (LIGHT WOOD) represents a habitat type that could potentially serve as a population sink for scrub lizards and recommend several methods to reduce the accumulation of CWD or to ameliorate its potential thermal stress on lizards. In addition, the most favored mesocosm side (DARK SAND) represents a shaded sandy habitat type not currently found in ONF timber stands. We present several alternative harvesting and site preparation methods that could produce such habitats and recommend further research on their potential value for enhancing populations of scrub lizards and other open-habitat scrub

Dominance status in birds may involve a trade-off in foraging costs and benefits. This study tested the hypothesis that the cost of being a subordinate species may be offset by the benefit of being better at finding novel food locations compared to their dominant competitors. In a pair of flight-cage experiments, the ability of two tropical hummingbird species to find novel locations of food was measured. A dominant species (steely-vented hummingbird,Amazilia saucerottei) and a subordinate species (fork-tailed emerald,Chlorostilbon canivetii), tested both as solitary birds and in competing heterospecific pairs, did not differ significantly in (1) the time required to first discover novel food locations, (2) the number of feeding visits made to such sources or (3) the number of novel food locations one bird could discover before its cage-mate. The dominantAmazilia, however, was twice as fast asChlorostilbonat finding novel food locations previously discovered by a competing heterospecific cage-mate. This behaviour pattern could facilitate the pre-emption of newly found food sources fromChlorostilbonin the wild. Other possible mechanisms that could confer an advantage on the subordinate species are discussed: (1) ability to locate cryptic food sources, (2) ability to recognize as food a novel item that has never been used before and (3) specialization on finding food sources that dominant species cannot pre-empt.

The ecological risks of pesticides to wildlife are assessed by the United States Environmental Protection Agency with a simple quotient model. A risk factor is calculated by dividing the estimated dietary concentration by the chemical’s dietary toxicity. The risk factor, which can be used to predict population mortality, serves as a regulatory criterion to identify compounds that could pose unacceptable risk. Under the “New Paradigm,” the Environmental Protection Agency recently cut by 50% the critical risk factor, yielding more‐rigorous decision‐making criteria by decreasing acceptable wildlife mortality from 50 to 8.8% following one pesticide application and by increasing the number of pesticides that pose unacceptable risk to wildlife. The quotient model depends on at least one implicit and approximately 11 explicit assumptions; deviations from these assumptions may bias outputs and consequent regulatory decisions. To correct error‐prone assumptions we present three modifications that improve ecological risk estimates. We used the agency’s quotient model to survey risks to a regional avifauna (Florida birds) in relation to mosquito pesticide exposure (fenthion, malathion, and naled). Certain groups (small‐bodied, insectivorous passerines) were predicted to face the highest ecological risk due to taxonomy, diet, and body mass. Finally, we performed a risk assessment for Black‐whiskered Vireos (Vireo altiloquus barbatulus) exposed to fenthion. The results revealed that this species could potentially suffer 42% mortality in a population exposed to one application of fenthion. Ecological risk assessments increasingly will be based on mathematical models. To improve predictions of the effects of xenobiotic compounds on wildlife, biologists‐especially conservationists‐should work with ecotoxicologists to improve current models, develop new models, and provide data to parameterize models. Equally important, conservationists should participate in defining regulatory levels of ecological risk for wildlife.

The goal of this study was to measure directly the acquisition and allocation of energy for competing hummingbirds. In flight-cage trials providing an easily defensible food source, complete energy budgets (intake, expenditure, and storage) were obtained for two sympatric Costa Rican hummingbirds: a territorial (Amazilia saucerottei) and a low-reward traplining (Chlorostilbon canivetii) species. Behavior and energy responses of solitary birds (controls) were compared to the responses of conspecific and heterospecific pairs competing for a single feeder.Relative to controls, birds in pairs generally spent more time in flight, due primarily to increased rates of visiting the feeder or to agonistic encounters, with a consequent increase in energy expenditure. Ability of birds in pairs to compensate for increased expenditures by increasing intake, thus maintaining a constant body mass over 24 h, depended upon species and dominance status. The greatest asymmetries in energy effects occurred in heterospecific pairs, in which Amazilia aggressively interfered with access to the feeder by Chlorostilbon. In these trials, Amazilia boosted intake sufficiently to maintain adequate rates of energy storage; Chlorostilbon did not increase intake and thus suffered significant loss of energy stores. Conspecific pairs of each species experienced energy effects intermediate to the extreme responses of heterospecific pairs. Individuals of either species had greater energy success when paired with a Chlorostilbon rather than with an Amazilia. For both species, individuals that were relatively more aggressive than their cagemates experienced the greater energy success, though absolute frequency of aggression by an individual was a poor indicator of its energy success. Differential energy response to competition by Amazilia and Chlorostilbon appears to be one mechanism that contributes to local species abundance and guild composition.

Two tropical hummingbird species with divergen foraging modes and competitive strategies were tested for energetic and behavioural responses during food competition. In a large flight cage, heterospecific pairs competed for limited food (sucrose solution) delivered to five artificial flowers (feeders) arranged in two food-density treatments. When feeders were tightly clumped, the dominant territorial species (the steely-vented hummingbird, Amazilia saucerottei) actively defended them, thereby reducing access by the subordinate ‘traplining’ species (the fork-tailed emerald, Chlorostilbon canivetii). As a consequence, the dominant species maintained relatively high mass-specific rates of energy intake (J/g/h) and a balanced energy budget; whereas the trapliner maintained low food intake, high energy expenditures, and suffered negative energy balance. When feeders were widely dispersed and infefensible, the trapliner obtained food at a higher mass-specific rate than the territorialist, but again suffered negative energy balance as a result of excessive energy expenditure. In contrast, the territorialist had low intake and expenditures, thus maintaining energy balance. Regardless of treatment, both species changed their behaviour in similar ways over the feeding day, reducing (1) visit rate to feeders, (2) diversity of feeders visited, (3) overlap between cagemates in feeders visited, and (4) time spent flying. After repeated interactions, each cagemate eventually concentrated its foraging on a disjunct subset of feeders, thus enhancing foraging profitability while partially mitigating the negative energetic impacts of competition for limited food.

Because hummingbirds are extremely sensitive to energy stress, yet often face conditions when energy intake is reduced or energy expenditures must be increased, they should have flexible energy budgets. I experimentally measured the ability of two syntopic tropical hummingbird species to manage daytime energy budgets under conditions simulating natural foraging constraint, defined here as low nectar secretion rate, low flower density, or both. I tested a territorial species, Amazilia saucerottei, and a traplining species, Chlorostilbon canivetii, individually in a large flight cage at two rates of food delivery (HIGH = ad libitum, LOW = 64% of ad libitum) and two perch—to—feeder distances (NEAR = 4 m, FAR = 20 m). Both species increased flight time when distance was increased (FAR > NEAR by 44%) and when rate of food delivery was reduced (LOW > HIGH by 23%). However, birds on the HIGH food delivery rate did not increase food intake to compensate for increased flight expenditures to the FAR feeder. Birds on LOW food maintained total rates of energy expenditure that were less than birds on HIGH food, and LOW food birds experienced no effect of feeder distance on expenditure. These results appear to be due primarily to short—term reductions in perching metabolic rates (PMRs) by birds on LOW food or with the FAR feeder. Reduced daytime PMRs helped to mitigate the potentially negative impacts of foraging constraint: rates of mass loss of the LOW food birds were an estimated 48% less than if birds had maintained normal PMRs. Reduced PMRs also enabled birds visiting the HIGH FAR feeder to maintain rates of mass gain equal to unconstrained birds (HIGH NEAR feeder). Relative differences between species in energy management reflected their foraging models. The low—reward trapliner paid the greatest energy costs at LOW food, regardless of distance, due to its overall tendency for high flight time. In contrast, the territorialist did poorly in the HIGH FAR treatment, due to flight expenditures associated with defending a rich but dispersed resource. Although individual birds exhibited considerable flexibility in energy management, the foraging mode represented by each species appeared to be energetically specialized for particular levels of food availability and dispersion.

We validated the doubly labeled water (DLW) method for a tropical hummingbird (Amazilia saucerottei) in a humid environment. We compared daily water influx and energy intake, expenditure, and storage using two independent techniques: the DLW method (using (3HH18O)-O-18 [HTO-18] with and without fractionation corrections) and a gravimetric method. Uncorrected DLW values differed significantly from gravimetric values, with water influx 4.5% lower, energy intake 4.6% lower, and energy expenditure 15.1% higher than for the gravimetric method. In contrast, the corrected DLW values were statistically equivalent to the gravimetric values, with differences ranging from 1.5% lower to 0.1% higher. This suggests that physical fractionation of isotopes during evaporative water loss was appreciable but that corrections based on published fractionation constants yielded highly accurate DLW estimates. We conclude that two potential problems in using the DLW method on tropical hummingbirds, water vapor input from humid air and dynamic biological effects from high rates of water turnover and energy metabolism, did not contribute significant error to DLW estimates corrected for fractionation.

At Monteverde, Costa Rica, the plants Besleria triflora (Gesneriaceae), Palicourea lasiorrachis, and Cephaelis elata (both Rubiaceae) share hummingbirds (Lampornis calolaema) as pollinators. To investigate the effect that intervening visits to Cephaelis flowers have on pollen transfer between plants of self-compatible Besleria or of self-incompatible Palicourea, we presented captive Lampornis with series of hand-held flowers: first, 2 or 15 flowers of either Besleria or Palicourea as pollen donors, followed by 0, 2, or 10 Cephaelis flowers, followed by 20 recipient flowers of the first species. In protandrous Besleria, we used male-phase flowers as donors and female-phase flowers as recipients. In distylous Palicourea, we used pin (long-styled) flowers as donors and thrum (short-styled) flowers as recipients. We assessed pollen transfer by counting pollen tubes in recipients' styles and, in Besleria, by counting pollen grains deposited on stigmas.Intervention of Cephaelis flowers strongly reduced pollen transfer among Palicourea flowers. Increasing the number of donor Palicourea flowers significantly increased the absolute amount of pollen transferred but did not overcome the negative effect of Cephaelis. Pollen transfer among Besleria flowers also declined with the intervention of Cephaelis flowers; the decline was less strongly significant than for Palicourea, perhaps because pollen loads on stigmas of some female Besleria flowers can contain self pollen left over from their male phase.Under controlled conditions, then, strong competition may exist where plants share pollinator individuals, a situation faced by the experimental species and many others at Monteverde. Other studies on these plants reveal that despite its demonstrability in the laboratory, however, competition among individual plants varies in its ability to explain density dependence in pollination among plant populations in the field. Furthermore, community-level patterns of coexistence among plant species at Monteverde feature few ''ghosts of competition past.'' The collective results demonstrate that studying the role of particular interactions in community structure must involve examinations of mechanisms at the level of individuals, processes at the population level, and patterns of coexistence rather than just one level of this hierarchy. Studying mechanisms alone could exaggerate their importance to community structure, whereas studying coexistence patterns alone could misjudge the strength of interactions among individuals.

Calcul du taux de passage alimentaire chez 2 especes d'oiseaux apres un repas unique ou une alimentation ad libitum. Etude du taux d'excretion, du taux de vidage du jabot, correlation avec la quantite d'aliment absorbee

The harmonic mean method was used to calculate activity areas. Mean home range size was 5.4 ha, with a very concentrated core area of only 7.7% of the home range. Recause most animals tested exhibited shifting activity centers, and because home range size was positively correlated with the number of days a snake was tracked, it was concluded that N. sipedon at this site did not maintain a home range in the traditional sense. A dynamic methodology for quantifying areal utilization is proposed. N. sipedon was found to be very selective in its habitat utilization. Cattails (Typhus latifolia) and flooded meadow (primarily Phalaris and Carex spp.) were generally prefet ed in excess of availability, while open water was avoided. Dead cattail clumps were the most utilized substrate. Water (surface and submerged) and grass (dead and live) were also preferred to a lesser extent. Seasonal and daily trends are discussed in terms of responses to exogenous and endogenous cycles. Diversity of substrate use peaked during morning hours and showed an overall increase as the season progressed. Mean perch height was 10.9 cm above water, without strong differences among daylight hours. Perch heights were greatest during May; in habitats along open water; and on branches, dead cattails, and dead logs. The mean insolation level was 50.9%. On a daily cycle snakes received more sunlight during the midday hours, but it appeared snakes were not responding passively to decreased shade availability. Perch height and insolation level were positively correlated, thus high substrates were also associated with greater insolation. Three measures of snake activity were analyzed: incidence of movement (s = 27.7%), total rate of movement (? = 5.2 m/h), and conditional rate of movement (x = 18.7 m/h). Snakes were generally more active during April while they dispersed from the hibernaculum. From May-July the animals were equally active at all times of the day. Snakes exhibited greater rates of travel across open and exposed habitat types. Individual snakes differed significantly in all three measures of activity and also had variation in home range size spanning four orders of magnitude. Nevertheless, more active snakes did not utilize a larger area than their less active conspecifics.

Based on observations of Alcoholics Anonymous as its program has affected change in many members, and from clinical experience with alcoholic patients, a hypothesis is formulated concerning the effective psychological events which make possible the maintenance of sobriety. Four elements are recognized as playing an essential role: hitting bottom, surrender, ego reduction, and maintenance of humility. The application of this conceptualization in individual psychotherapy is discussed and illustrated with case material.