Peter Feinsinger

A Simple Measure of Niche Breadth

Niche breadths in animal and plant populations are often measured without regard to the relative frequencies of the various resources available to the organisms. Recent papers have provided more accurate indices for use when available resources can be quantified. These indices may lack wide applicability or simple biological interpretations. We suggest that niche breadth be defined as the degree of similarity between the frequency distribution of resources used by members of a population and the frequency distribution of resources available to them. Similarity can be quantified with the familiar Proportional Similarity (PS) Index. This index, which measures objectively the similarity between two frequency distributions, reflects in satisfactory fashion the breadth of a populations niche. See full-text article at JSTOR

On the calculation of sugar concentration in flower nectar

SummaryThere are several sources of potential error in calculating the concentration or energy value of floral nectar. Errors resulting from confusing data become substantial with increasing concentration. The different methods of expressing sugar concentration are here clarified, and the correct methods of converting from one to the other are provided. Refractometers in use in field studies usually read on a weight per total weight basis; this is recommended as the mode of statement. The perils of oversimplifying conversions from this mode, as is often done, are pointed out.

Effects of plant species on each other's pollination: Is community structure influenced?

Pollination is one of the most important aspects of the life histories of most vascular plants. Until recently, there has been a broad consensus that heterospecific neighbors compete for pollinators, that this competition leads to phenological divergence, and that divergence leads to structured communities. New work is revealing a more complex web of interactions.

Elevation and the Morphology, Flight Energetics, and Foraging Ecology of Tropical Hummingbirds

The power that a hummingbird must expend to hover increases with decreasing air density and therefore with increasing elevation. Equations are available for estimating this power output requirement and for computing the easily obtained parameter of wing disc loading (ratio of body weight to area of disc whose diameter is wing span), to which power output is directly related. We test four related predictions based on these equations and on empirical patterns of exploitation versus interference competition among hummingbirds. (1) Species having the same morphology over broad elevational range are expected to engage in more interference competition at high elevations. (2) The allowable extremes of power output for hovering should be relatively constant with elevation. (3) Mean wing disc loading of hummingbird assemblages should decrease with increasing elevation. (4) The mean power output among hummingbird assemblages should not vary with elevation. Tests with field data verify the last three predictions; although independent data for testing the first prediction directly are not yet available, its validity is confirmed by a clearcut corollary. These results imply a precise interrelationship between hummingbird behavior, morphology, energetics, and competition.

Island Ecology: Reduced Hummingbird Diversity and the Pollination Biology of Plants, Trinidad and Tobago, West Indies

To examine effects of pollinator diversity on pollination biology of plants, we studied early successional, hummingbird-pollinated plants for 13 mo on Trinidad and Tobago. A large, land- bridge island just off the Venezuelan coast, Trinidad has 16 hummingbird species. Smaller and more isolated, Tobago has a subset of five of these. Study sites in the Arima Valley on Trinidad had 17 species of plants adapted for hummingbird pollination; 12 of these, plus one other, existed on com- parable Tobago sites. From hypotheses of island ecology and plant-pollinator coevolution, we developed four predic- tions; results supported the first three: (1) Overall, among the eight plant species observed at least 4 d (up to 28 d) on each island, Tobago flowers received significantly fewer visits than nonspecific Trinidad flowers from hummingbirds and the Bananaquit Coereba flaveola, the only other avian visitor. A two-way ANOVA showed that the treatment (island) effect significantly exceeded even the tremendous month-to-month, plant-to-plant variation in visits received within each plant population. (2) Pollen loads carried by hummingbirds and Bananaquits on Tobago tended to be mixed, whereas birds on Trinidad often carried single-species loads. (3) In two of three plant species studied inten- sively, Tobago flowers secreted greater volumes of nectar than Trinidad flowers. The third species showed a slight but significant increase as well. An indirect measure of nectar standing crop, the time a hummingbird spent probing a flower, suggested that Tobago plants as a group secreted higher nectar volumes than Trinidad conspecifics. We found no significant differences in sugar concentration, how- ever. (4) Contrary to predictions that flowering seasons should overlap less on Tobago than on Trinidad, there was no discernible difference in flowering seasons between Trinidad and Tobago conspecifics. Evidently, pollination service on Tobago is currently more erratic than on Trinidad, and has been sufficiently erratic in the past to select for increased nectar production but not so erratic as to override other, stabilizing, selective forces on flowering times.

Spatiotemporal Patterns of an Irruption and Decline of Small Mammals in Northcentral Chile

During the austral winter of 1987 (June–August) at a semi-arid site in northcentral Chile, an outbreak of small mammals apparently was triggered by one episode of unusually high rainfall. From October 1987 to November 1990, we monitored the outbreak on a monthly basis on two equatorial- and two polar-facing slopes. Overall density on equatorial-facing slopes was 239 individuals/ha in spring 1987, increasing to a peak of 404/ha by summer 1988, and then steadily declining to a crash of 20/ha (5% of peak density) by spring 1990, with no signs of recovery. On polar-facing slopes, mammalian abundances were about one-half those of equatorial-facing slopes. There were 112 individuals/ha in spring 1987, increasing to a peak of 199/ha by summer 1988, and then steadily declining to a crash of 8/ha (4% of peak density) by spring 1989. Since then, mammal populations on polar-facing slopes have been slowly recovering, reaching 11% of their peak density by November 1990. Of the eight species monitored, only three irrupted: the granivorous cricetid Phyllotis darwini , the omnivorous cricetid Akodon olivaceus , and the insectivorous didelphid Marmosa elegans . These three irrupted and declined in phase, simultaneously on the two opposite-facing slopes, such that their relative frequencies did not shift markedly. Two of the three folivores ( Abrocoma bennettii, Octodon degus , but not Chinchilla lanigera ), one granivore ( Oryzomys longicaudatus ), and one insectivore ( Akodon longipilis ) disappeared from the site, persisting longer on equatorial-facing slopes.

Competition for the Nectar of Centropogon valerii by the Hummingbird Colibri thalassinus and the Flower-Piercer Diglossa plumbea, and Its Evolutionary Implications

In the highlands of southern Costa Rica, one of the commonest native plants of second-growth areas is Centropogon vu&i Standl. ( Lobeliaceae), a perennial shrub with orange-red tubular flowers (Wilbur 1972). Although some flowers are produced by C. vu&i in all months of the year, in the dry season (December through March) a single plant may have over a hundred open flowers on a continual basis. During this flowering peak, most large clumps of C. vale&i are pollinated primarily by the Green Violet-ear ( Co&i thalussinus cubunidis) (Trochilidae). This hummingbird is an altitudinal migrant, spending the rest of the year at lower elevations (Skutch 1967; Slud 1965; see also Wagner 1945; Wolf and Stiles 1970). In the highlands, the male violet-ear often sets up a territory around patches of C. u&r%, which he defends vigorously against others of his own species, as well as hummingbirds of other species (Colwell 1973; Wolf 1969; Wolf and Stiles 1970). In what must be among the earliest descriptions of territoriality in hummingbirds, Boucard (1878) said of this species: “They take possession of a certain space containing several of these shrubs [very likely Centropogonl; and when not feeding on these flowers, they perch on a dry branch near the place, and fight all the other Humming-birds that dare to intrude.” Besides other hummingbirds, the Green Violet-ear has two additional potential competitors for the nectar of C. vuletii, both of them nonpollinating nectar thieves. The Slaty Flower-piercer (Diglossu plumbea) (“Coerebidae”) punctures the base of the corolla with its lower mandible and extracts nectar with its tongue, often while perching on the pedicel (in C.

Effects of indiscriminate foraging by tropical hummingbirds on pollination and plant reproductive success: experiments with two tropical treelets (Rubiaceae)

SummaryIn cloud forest at Monteverde, Costa Rica, two common treelets (Palicourea lasiorrachis and Cephaelis elata, both Rubiaceae) depend simultaneously on one hummingbird population (Lampornis calolaema) for pollination. Both species are distylous and self-incompatible. In laboratory experiments, we examined possible effects of indiscriminate foraging by hummingbirds among flowers of both species, as observed in the field, on pollination of Palicourea. In each of 35 trials, captive L. calolaema probed 2 flowers from pin plants of Palicourea followed by 20 thrum flowers of the same species, with either 0, 2, or 10 Cephaelis flowers intervening. We assessed pollen transfer by staining and counting pin pollen tubes growing in thrum styles; counts of 0, 1, or ≥2 pollen tubes relate directly to seed output (0, 1, or 2 seeds per fruit, respectively). Intervening Cephaelis flowers sharply reduced pollen receipt by thrum flowers of Palicourea and reduced some aspects of pollen dispersal from pins as well, thereby curtailing maternal and paternal reproductive potential of Palicourea. Such effects of interspecific pollen loss on reproductive output may lead to strong competition among some, though not all, combinations of plant species pollinated by L. calolaema or of other plant combinations that share animal pollinators.

Professional ecologists and the education of young children

Efforts to conserve natural habitats and their non-human occupants, a concern of most ecologists and evolutionary biologists, are ultimately futile unless there is a change in concepts and attitudes among decision-makers throughout the general public, from subsistence farmers to presidents of multinational corporations. One way to encourage this change is to upgrade the biological and environmental education that children receive.