bluuebunny/crossref_metadata_2025 huggingface dataset:
Darwin's Finches (Geospiza) On Isla Daphne Major, Galapagos: Breeding and Feeding Ecology in a Climatically Variable Environment
Authors: Boag Peter T. , Grant Peter R.
Published: April 2006

The Darwin's finches on Isla Daphne Major, Galapagos, were studied between July 1975 and June 1978. Geospiza fortis and G. Scandens are residents, while G. fuliginosa and G. magnirostris are regular immigrants. The Daphne climate is unpredictably dry. The island has a simple plant community displaying marked annual and spatial variation in the foods which form finch diets. Breeding is stimulated by rain falling irregularly between January and April; G. scandens laid eggs with as little as 16 mm of rain, but G. fortis required 35 mm or more before laying. G. scandens consistently bred prior to the rains, associated with specialized exploitation of dry season Opuntia cactus flowers. The breeding system of both species was similar to that of other Geospiza species: monogamous matings on small, permanent, all—purpose territories. Reproductive output of both species varied. In 1976 single broods were produced by both species at high densities, with modes of three young. In 1977, only 24 mm of rain fell during the breeding season and G. scandens alone bred, with poor success. By 1978, G. scandens populations had declined by 66% and G. fortis by 85%. In 1978, both species laid an average of three clutches per pair, with a mode of four young per brood. During the 1977 drought, the sex ratio became skewed in favor of males in both species, and as a consequence some females bred successively with up to three different males in 1978. The skewed sex ratio retarded population recovery following the drought. The population decline was associated with a decline in seed abundance in the drought. As food disappeared, G. fortis diets widened to include a broad selection of food items, while G. scandens diets contracted to Opuntia seeds. Even in normal years, both species showed pronounced seasonal variation in feeding habits. Both fed heavily on Opuntia flowers in the late dry season, followed by a mixed diet of insects, fresh seed, and other green matter during the breeding season. After breeding, the birds fed primarily on seeds, the two species selecting different proportions of the available range of seed sizes. Overall, G. fortis displayed the feeding, breeding, and population dynamics characteristic of an ecologically generalized species, whereas G. scandens is a highly specialized species. Large variation in food supply, caused by large variation in rainfall, is responsible for the presence of only two species with breeding populations, for large fluctuations in their population sizes, and for their large clutch sizes and opportunistic breeding. Long—term studies are essential for an understanding of communities in such variable environments because some important events are rare.
Foraging Ecology of the Striped Swamp Snake, Regina alleni, in Southern Florida
Authors: Godley J. Steve
Published: April 2006

The foraging ecology and trophic dynamics of the striped swamp snake, Regina alleni, were studied from 1974—1977 in a south Florida water hyacinth community. The mean standing crop of R. alleni was 30.79 kg (1289 individuals)/ha of water hyacinths. This biomass estimate is greater than that known for any snake species and is related to (1) the high primary productivity of water hyacinths; (2) the trophic positions, diets, and concomitant abundances of the snake's prey; (3) the availability of alternate habitats for exploitation; and (4) release from certain competitive and predatory pressures. Snake density was lowest in summer, increased in fall and winter, then decreased in spring. Changes in density apparently represent seasonal movements of snakes between the hyacinth habitat and the surrounding marshes, in response to fluctuations in water level, prey availability, and predator pressure. R. alleni showed dramatic seasonal and ontogenetic shifts in food habits. Young R. alleni (120—200 mm snout—vent length [SVL]) fed primarily on libellulid odonate naiads but switched to seasonally abundant palaemonid shrimp and astacid crayfish. Between 200 and 300 mm SVL a major dietary shift occurred and crayfish gradually replaced odonates and shrimp. This change occurs throughout the range of the species and also involves a reorganization of snake feeding behavior to accommodate prey of different shapes. The ecological and energetic consequences of this dietary shift are interpreted in terms of the divergent life histories and growth patterns of the predator and its prey. Within the specialized trophic niche of R. alleni, food availability and predator size largely determined the types and sizes of prey consumed, but interacted with the thermal regime, energetic requirements, and foraging efficiencies of individual snakes to determine the rate of food intake. In most seasons juvenile R. alleni consumed more but smaller prey than adults, and the mean percent of snake body mass eaten per day was higher for adults. However, because juveniles fed on odanate naiads that were higher in protein but lower in ash content than the decapods taken by adults, the energetic intake per gram snake body mass was generally higher in juveniles. The predatory impact of R. alleni may be a significant factor limiting the growth of both the snake and its prey populations. During fall, when measured rates of food intake were highest, adult R. alleni consumed °9.6% of the adult crayfish population. In contrast, juveniles accounted for removal of °90.7% of the odonate population in the same time period. When given an unlimited food supply in the laboratory, the daily energetic intake of juveniles was more than two times that of maximum field estimates.
Mining Pollution and the Diet of the Purple‐Striped Gudgeon Mogurnda mogurnda Richardson (Eleotridae) in the Finniss River, Northern Territory, Australia
Authors: Jeffree Ross A. , Williams Neville J.
Published: April 2006

During the dry season of 1974, collections of the purple—striped gudgeon Mogurnda mogurnda were taken from the Finniss River of the Northern Territory; during the wet season, this river receives acidic and metallic pollutants from the formerly mined area of Rum Jungle. The fish consumed a great variety of foods, with high abundances of Dytiscidae, Chironomidae, Ceratopogonidae, Trichoptera, Odonata, Copepoda, Decapoda, and Pisces. Within polluted and unpolluted zones of the river; the dietary abundances of some foods varied with the size of the consuming fish and with habitat descriptors. For no food was there a significant regression against habitat descriptors in both of the zones; this emphasizes that pollution effects are more complex than simply depression or raising the abundances of the dietary species. Five foods were more abundant in the diets of the polluted zone, and three in those of the unpolluted zone. The dietary abundances of two foods, both crustacean, increased in the polluted zone, compared to the unpolluted zone, through the dry season. Two categories of foods: (1) those obtaining oxygen directly from the atmosphere or via a film or bubble of air; and (2) the converse set (aquatic respirers), were contrasted for their usefulness in distinguishing between the zones, by both hierarchical agglomerative and discriminant function analyses. Aquatic respirers were the more effective. The polluted collections were more heterogeneous than the unpolluted ones in both the hierarchical and the discriminant analyses. One collection from the polluted zone was reclassified as unpolluted on the basis of its grouping behavior. The relevance for pollution studies of dietary analysis of euryphagous fish, rather than sampling aquatic fauna directly, is discussed in terms of food substitution, switching, strategies for abundance and recovery by the fauna, and possibly effects of the pollutants on the fish as an intervening collector. Downstream patterns of abundance of the invertebrate fauna in this study are broadly similar to those of other studies in which such chemically diverse metals as Pb, Zn, and Cu are the pollutants, but there are differences for some faunal components. Difficulties in the comparison and causal interpretation of results of pollution studies in the field stem from a lack of experimental data on tolerances to pollutants and causes of abundance of stream invertebrates. However, because of the great detail required in such data, more profit for purposes of prediction may derive from experimental multivariate studies on faunal assemblages.
Aggregation and Coexistence in a Carrion Fly Community
Authors: Ives Anthony R.
Published: April 2006

In this paper I combine experiment and theory to demonstrate that aggregation of carrion flies ovipositing among carcasses may facilitate coexistence in nature. The paper is divided into an experimental part and a theoretical part. In the experiment part, I present field experiments that show the aggregative pattern of carrion flies ovipositing among carcasses, as well as associated experiments that explore the behavior leading to these patterns. I also use experiments to quantify the strength of larval competition between Phaenicia coeruleiviridis (Calliphoridae) and Sarcophaga bullata (Sarcophagidae). In the theoretical part, I develop two methods that use these data to assess the effect of aggregation on competition in the field. From the first method, I predict that intraspecific aggregation of P. coeruleiviridis females causes a 26% decrease in the expected recruitment of P. coeruleiviridis and a 74% increase in the expected recruitment of S. bullata. As a result, within a single generation, intraspecific aggregation increases intraspecific competition and reduces interspecific competition. The second method for assessing aggregation involves a new mathematical formula that gives conditions under which species may coexist indefinitely. This formula requires estimates of only the degrees of intra— and interspecific aggregation among species; there is no need to estimate adult survival and larval competition. I use this second method to show that the minimum effect of aggregation on coexistence for five carrion fly species is equivalent to reducing the amount of larval competition between pairs of species by an average of 57%. Aggregation may therefore play a major role in explaining the coexistence of carrion fly competitors.
A Simulation Model of the Population Dynamics and Evolution of Myxomatosis
Authors: Dwyer Greg , Levin Simon A. , Buttel Linda
Published: April 2006

Myxoma virus was released into Australia to control the introduced European rabbit, Oryctolagus cuniculus. Within a few years after introduction, the virulence of the virus had declined to an intermediate level, while the resistance of field rabbits and increased sharply. In the nearly 40 yr since the disease was introduced, host resistance has continued to increase, while viral virulence has only recently begun to show signs of counter—increases in some areas. The two questions of interest are thus: Is this system in a coevolutionary arms race (Dawkins and Krebs 1979); that is, will both host and pathogen continue to evolve antagonistically? Will the virus continue to control the rabbit in the future? We present a simulation model based loosely on previous host–pathogen models (Anderson and May 1979), but with detailed accounting of the virus titer in infected hosts, and using realistic estimates of the demographic parameters of the rabbit, including age structure and seasonally varying reproduction. For a single virulence grade, by varying the non—disease (or "natural") mortality of the rabbit, the age at first reproduction of the rabbit, and the virulence grade of the virus, we explored the parameter range for which the rabbit population is controlled. For the most prevalent grades of the virus, grades IIIB and IV, the virus can control the rabbit for most realistic values of natural mortality and age at first reproduction. However, control is dependent on both natural mortality and virus virulence. Since natural mortality varies both geographically and seasonally, the usefulness of the virus may vary geographically and seasonally, and management policies must be sensitive to this variation. When competing against several virus strains that together encompass the complete range of virulence seen in the field, a strain of grade IV virulence competitively excludes strains of all other grades. This competitively dominant grade is close to the most prevalent virulence grades seen in the field. We discuss possible mechanisms of coexistence, including local competitive exclusion with global persistence, variability in host resistance, high mutation rates, and trade—offs between within—host and between—host competitive ability. By examining the effects of flea transmission efficiency, we are able to show that, contrary to commonly held belief, whatever effect fleas have upon the outcome of selection on virulence cannot be due to differences in transmission efficiency between fleas and mosquitoes. Finally, by including host resistance, we improve our prediction of the most prevalent grade of virulence. We conclude that control of the rabbit by the virus is likely for the near future, but that until we understand the genetics of resistance in the rabbit and the relationship between resistance and virulence for different grades of virulence, for different grades of virulence, we cannot make a useful prediction of the long—term state of this system.
Lunar Reproductive Cycles of Benthic‐Brooding Reef Fishes: Reflections of Larval Biology or Adult Biology?
Authors: Robertson D. Ross , Petersen Christopher W. , Brawn Jeffrey D.
Published: April 2006

Lunar reproductive cycles are common among marine animals. Most hypotheses concerning the adaptive nature of such cycles consider the effects of the tidal regime or moonlight on the dispersal of planktonic eggs or hatchlings away from adult habitats. We determined the reproductive periodicity of 17 paternal—brooding reef fishes at three neotropical sites with different tidal regimes. We used these and published data to assess the explanatory potential of hatchling—dispersal hypotheses, and of other larval—biology and adult—biology hypotheses. Among the 17 species (15 damselfishes and two blennies), two of which we studied at two sites, we found 14 with lunar and semilunar spawning cycles, one sporadically synchronized spawner, two acyclically variable spawners, and one continuous spawner. In 16 species individual nests experienced frequent alternation of short brood—care and rest periods (brood cycling). Simple hatchling—biology hypotheses are unable to account readily for the range of variation in the types, precision, and lunar timing of spawning cycles among species within and between depth zones at the same site, or for intra— and interspecific variation in spawning patterns in relation to seasonal and geographic differences in tidal regimes. The hypothesis that lunar spawning cycles have evolved to maximize the availability of relatively uniform—age larvae that settle during preferred lunar settlement times is supported by some but not all data. Adult—biology hypotheses can account for the higher frequency of lunar spawning cycles among brooders than nonbrooders, and can accommodate various patterns of reproductive cyclicism and synchronization in brooders. Synchronized activity may be favored in some brooders because colonial spawning provides enhanced defense against egg predators. Further, the cost of brood care may result in reduced egg survivorship, and both brood cycling and the temporal concentration of spawning may reduce egg losses by allowing males to recuperate and increasing benefits to brood—care for them. Adult—biology constraints may produce variability in spawning patterns. Differences in social systems may determine the ability to form nesting colonies, and to strongly synchronize spawning independently of lunar cues. Changes in short—term food availability may influence the regularity of spawning. Adult—biology hypotheses represent generally underemphasized alternatives that have at least as much explanatory potential as larval—biology hypotheses. If hatchling biology is of general importance to paternal brooders, there must be considerably more interspecific variability in hatchling ecology than is generally assumed.
Interaction of Fire and Community Development in Chaparral of Southern California
Authors: Riggan Philip J. , Goode Suzanne , Jacks Paula M. , Lockwood Robert N.
Published: April 2006

Fire is an ecosystem property rather than an exogenous force in southern California chaparral, and it interacts with processes of drought—mediated canopy development, production, and mortality to affect stability of community composition. Where species that must reproduce from seed, such as Ceanothus crassifolius or Ceanothus oliganthus, are predominant, composition can be altered by a single fire with little or no recruitment after initial postfire establishment. Water balance apparently regulates subsequent leaf area development; after 15—22 yr of postfire growth, foliage biomass in monospecific C. crassifolius stands in this study had approached a maximum that was unrelated to incident solar radiation and insensitive to initial population density over a 10—fold range. Thus, establishment success, above that required for canopy closure, should have little effect on the foliage biomass that sustains combustion. After canopy closure, total biomass accumulated at an accelerating rate through at least two decades with aboveground net primary production as great as 12—13 Mg · ha—1 · yr—1. C. crassifolius mortality was substantially less than predicted from growth rates and the —3/2 power model of Yoda et al. (1963), and there was no approach to a common asymptotic density by stands of disparate initial density. With low deadwood biomass and absence of ground fuels, c. crassifolius cannot sustain burning in the absence of wind, steep slopes, or exceptionally low live—fuel moisture. Increased Ceanothus abundance in multispecies communities with Adenostoma fasciculatum or Salvia mellifera alters biomass structure and could modify subsequent fire effects even if foliage area fully redevelops in concert with site water balance. Rare, low—intensity fires can devastate Ceanothus chaparral, that reproduces only from seed. Salvia mellifera and Eriogonum fasciculatum can occupy resulting openings in the canopy, and their abundant deadwood and compact biomass can readily spread low—intensity fires, thereby perpetuating the degraded community. Productive stands within a chaparral association are probably subject to especially severe fires that limit nutrient accumulation and may also limit subsequent productivity. Copious nitrogen volatilization during burning is promoted by high nitrogen concentrations in foliage and fine woody biomass of Ceanothus and heavy leaf litter of Quercus dumosa and C. crassifolius. The communities most prone to severe fires also accumulate and cycle nitrogen and phosphorus rapidly.
The Export of Nutrients and Recovery of Stable Conditions Following Deforestation at Hubbard Brook
Authors: Bormann F. H. , Likens G. E. , Siccama T. G. , Pierce R. S. , Eaton J. S.
Published: April 2006

We report the effects of deforestation on the export of particulate matter, erodibility of the ecosystem, and the relative importance of dissolved substances and particulate matter in exported materials. The mature forested ecosystem is little affected by erosion, with an average annual particulate matter export of only 2.5 MT (metric tons) km—2 yr—1. Deforestation and repression of growth for 3 yr increased export to a maximum of 38 MT km—2 yr—1, but the increase in export was exponential with rather minor increases in the first 2 yr after cutting and a sharp increase in the 3rd yr. This resulted because the ecosystem continued to exercise considerable control over erodibility for 2 yr after cutting without annual renewal of biotic regulation by primary productivity. Increases in particulate matter export are primarily due to increases in erodibility rather than increased flow rates. In the mature ecosystem, the average ratio of annual net export of dissolved substance to particulate matter is 2.3. Deforestation shifts this ratio to >8.0 during the first 2 yr after cutting. This shift results because the export trends, for dissolved substances and particulate matter following deforestation, are not synchronous. The first response to deforestation is mobilization of nutrients from the available nutrient and organic matter compartments and leakage in stream water. After 2 yr, particulate matter output rises sharply as biotic control of erodibility weakens, while dissolved substance export declines, probably because of diminution of readily available nutrients stored within the system. This nonsynchrony, coupled with the action of natural species adapted to take advantage of the abundance of nutrients and water that results immediately after disturbance, may be considered as part of a homeostatic mechanism that allows rapid recovery of a forest ecosystem while minimizing the effects of erosion. Thus, following destruction of the vegetation, the ecosystem maintains a residual resistance to erosion and has a high potential for repair through successional productivity. Nutrient flux and erosion losses return to previous levels as the intrasystem aspects of the hydrologic—nutrient cycle interaction and erodibility are increasingly regulated by biotic factors. These results relative to stable conditions and their reestablishment following disturbance may have applicability to a wide range of terrestrial ecosystems.
The Habitats of 17‐Year Periodical Cicadas (Homoptera: Cicadidae: Magicicada Spp.)
Authors: Dybas Henry S. , Lloyd Monte
Published: April 2006

Three species of 17—yr periodical cicadas–Magicicada septendecim (Linnaeus), M. cassini (Fisher), and M. septendecula Alexander and Moore–have ranges that are coextensive except around the edges. All the cicadas occurring together are the same age and emerge in the same 17th yr (hence they are "periodical"), yet populations in different parts of the range (called "broods") are out of phase with one another. Within the same brood, the three species are always perfectly synchronized, but they are separated microspatially by having different habitats within the same woodland. Magicicada septendecula prefers ovipositing in hickories and walnuts, and emerges in higher proportions under those trees than under comparable oaks. Both M. septendecim and M. septendecula occur together in upland woods, but septendecim exhibits much less host specificity than septendecula. The latter species is much rarer than septendecim; it can usually be heard chorusing in local patches within a woods occupied by septendecim. Magicicada cassini is a species of floodplain woods, and characteristically can be seen to replace septendecim and septendecula as one moves down a wooded slope leading to a stream. Over much of the eastern United States, however, the original forest has been extensively disturbed. Periodical cicadas survive and reproduce surprisingly well in cutover, scrubby second growth. Tree species characteristic of floodplains, like American elm, are often a component of upland second growth, and, especially in such situations, cassini, septendecim, and septendecula become intermixed though they remain reproductively isolated. The present lack of microspatial separation in many situations, then, is an artifact of human disturbance. Even so, on the edges of the range where only one species occurs, it does not invade the habitat of the other, even though its "competitor" is absent. These assertions are based on 4 yrs of summer field studies, from 1962—65 on Broods II, III, IV, and V primarily in Virginia, Iowa, Kansas, Oklahoma, and Ohio, and later, more cursory observations in 1968—70 on Broods VIII, IX, and X in Pennsylvania, West Virginia, and Indiana, as well as on previous studies by ourselves and others reported in the literature.
Relationships Between Landscape Structure and Breeding Birds in the Oregon Coast Range
Authors: McGarigal Kevin , McComb William C.
Published: April 2006

Human—caused fragmentation of forests is increasing, yet the consequences of these landscape changes to vertebrate communities are poorly understood. Although bird community response to forest fragmentation caused by agricultural or urban development has been well studied, we have little understanding of these dynamics in landscapes undergoing intensive forest management, where late—seral forest stands are separated by younger forest stands of varying ages and are part of a spatially and temporally dynamic forest landscape. We investigated the relationship between landscape structure and breeding bird abundance in the central Oregon Coast Range. We sampled vegetation and birds in 30 landscapes (250—300 ha) distributed equally among three basins. Landscapes represented a range in structure based on the proportion of the landscape in a late—seral forest condition and the spatial configuration of that forest condition within the landscape. We computed a variety of landscape metrics from digital vegetation cover maps for each landscape. Using analysis of variance and regression procedures, we quantified the independent effects of habitat area and configuration on 15 bird species associated with late—seral forest. Species varied dramatically in the strength and nature of the relationship between abundance and several gradients in habitat area and configuration at the landscape scale. Landscape structure (composition and configuration) typically explained <50% of the variation in each species' abundance among the landscapes. Species' abundances were generally greater in the more heterogenous landscapes; that is, they were associated with the more fragmented distribution of habitat. Only Winter Wrens showed evidence of association with the least fragmented landscapes. These results must be interpreted within the scope and limitations of our study. In particular, the scale of our analysis was constrained by the lower and upper limits of resolution in our landscapes, as set by minimum patch size and landscape extent, respectively. Thus, our results do not preclude much stronger and different relationships at finer and/or coarser scales. In addition, our community—centered habitat classification scheme and artificially discrete representation of patch boundaries may not have captured the functionally meaningful heterogeneity for each species. Finally, our analysis was limited to relatively common and widespread diurnal breeding bird species. Species sensitive to habitat fragmentation at the scale of our analysis may have been rare already and therefore not subject to the parametrical statistical approach that we employed.
The Genetic Component in Plant Size Hierarchies: Norms of Reaction to Density in a Polygonum Species
Authors: Thomas S. C. , Bazzaz F. A.
Published: April 2006

An important motivation for the study of variability in size and reproductive output in plant populations is its potential relation to natural selection. However, very few data are available to assess the genetic component of fitness—related traits in competing plant populations, or the differential performance of plant genotypes at different densities. To address these issues we conducted an experiment using 25 genotypes of a colonizing herbaceous annual, Polygonum pensylvanicum. These genotypes were randomly sampled from a natural population and cloned by axillary meristem enhancement. Cloned plants were grown in a glasshouse at three densities spanning the range encountered in the natural population (from individually grown to 850 individuals/m2). The growth and fate of a total of 1400 individuals were followed over the course of a 10—wk growing period. Variability in size and reproductive output (as measured by the coefficient of variation of vegetative and reproductive dry mass) increased with density. Early plant size measures were positively correlated with subsequent relative growth rates in dense populations, but not among individually grown plants. These observations indicate the likely importance of asymmetric or "one—sided" competition in the dense populations. The proportion of variance in final size and reproduction explained by genotype was generally higher for individually grown plants than for plants grown under crowded conditions. We suggest that this may result from asymmetric competitive interactions working to amplify early size differences resulting primarily from environmental and developmental "noise." The same genotypes were not superior across all densities. Qualitative ("cross—over") interactions for fitness—related characters were observed in comparing genotype performance between the individually grown vs. the low and high density treatments. Genotypes with an early size advantage were predictably favored in dense populations, but the genetic correlation between early and final performance was weaker among individually grown plants. In sum, density increased relative variation in fitness correlates such as reproductive biomass, but decreased the heritability of these traits. The response of selection is the product of these two opposing forces. Applying our results to some elementary quantitative genetic models suggests that the potential for natural selection would increase with population density, while the potential for genetic drift would decrease. Such patterns may be of particular evolutionary importance in colonizing annuals, whose life histories imply an alternate exposure of genotypes to high and low densities.
Comparative Demography of Three Species of Scleractinian Corals Using Age‐ and Size‐Dependent Classifications
Authors: Babcock Russell C.
Published: April 2006

Three species of massive reef—building coral, Goniastrea aspera, G. favulus, and Platygyra sinensis, were studied on two fringing reef flats in the central Great Barrier Reef from 1982 to 1984. Total population sizes ranged from 25 to 292 colonies, and remained relatively constant. Population structures and dynamics based on both age and size were described. Differences between these two classifications were primarily due to tissue fission or shrinkage of colonies. In populations dominated by small size classes, young corals were not necessarily the most abundant. Similarly, populations dominated by the largest size classes were not always dominated by the oldest corals. In several populations, mean colony size decreased slightly with increasing age, though variability in size also increased. Mortality patterns were similar in all three species, with the youngest genets and smallest ramets suffering the highest death rates. While mortality in older or larger corals was low, the incidence of partial mortality and fission was higher in these groups. Age—specific fecundity increased rapidly once reproductive age was reached at ≈5 yr, but fecundity decreased slightly in the older age classes due to the decrease in mean colony size. Estimated mean generation times ranged from 33 to 37 yr.
Long‐Term Experiments on Calanoid‐Cyclopoid Interactions
Authors: Soto Doris , Hurlbert Stuart H.
Published: April 2006

Zooplankton species composition was manipulated in an 8—mo long series of experiments in outdoor 450—L tanks. The first experimental stage evaluated the impact of cyclopoids (Mesocyclops, Microcyclops, Cyclops) and calanoids (Diaptomus) on each other. The second and third stages evaluated the effects of Daphnia and mosquitofish (Gambusia affinis) on the calanoid—cyclopoid interaction. Cyclopoid predation initially caused a 50—70% reduction in calanoid abundance. After a few months, however, cyclopoids caused >300% increases in calanoid abundance, apparently by preventing calanoid overexploitation of the phytoplankton. The presence of calanoids depressed cyclopoid abundance by up to 70—90%, presumably by diminishing the availability of edible phytoplankton to cyclopoid nauplii and of prey, such as rotifers, to cyclopoid adults. The presence of Daphnia depressed calanoid abundance, probably by reducing the phytoplankton abundance, but did not affect cyclopoid abundance, perhaps because cyclopoid adults could feed on items other than phytoplankters. Coequality (i.e., similarity in abundance) of closely related taxa was in 4 of 5 cases favored by the addition of a more distantly related taxon. Thus the addition of cyclopoids favored the coequality of two Diaptomus species (D. clavipes, D. siciloides), the addition of these Diaptomus species favored the coequality of two cyclopoid genera (Mesocyclops, Microcyclops), and the addition of Daphnia favored coequality of cyclopoids and calanoids and coequality of the two Diaptomus species, but the dominance of Microcyclops over Mesocyclops. Effects of Gambusia included a drastic reduction of Daphnia populations, moderate reduction of calanoid populations, and negligible effects on cyclopoid populations.
The Influence of Adults of Some Coral Reef Fishes on Larval Recruitment
Authors: Sweatman Hugh P. A.
Published: April 2006

I examined the recruitment of reef fishes to isolated experimental standard—size coral colonies supporting residents of each of four planktivorous fishes: (a) Dascyllus aruanus, (b) D. reticulatus (both at several densities), (c) Chromis caerulea, or (d) Pomacentrus popei. I removed all recruits at approximately weekly intervals, and summed larval recruitment over each of two settlement seasons. I found two types of interactions between resident fishes and recruits: (1) There was increased settlement of three species in sites where there were resident conspecifics. This appears to be due to habitat selection by settling larvae. More larval D. aruanus, D. reticulatus, and C. caerulea recruited to corals with resident conspecifics than to corals with other congeners or vacant control corals. In addition, corals with the highest densities of resident D. aruanus and D. reticulatus received the most conspecific recruits. (2) The presence of high densities of resident D. aruanus and D. reticulatus reduced recruitment of heterospecific larvae in all cases for which data were sufficient to allow a powerful test. The presence of C. caerulea reduced recruitment of some species but not others. This interspecific effect could be due to habitat selection by settling larvae, and/or emigration and mortality caused by aggressive interactions with residents. Some species were unaffected by the presence of resident P. popei, but the data for most species were inconclusive. Interactions of the first type may be the cause of the clumped distributions of other reef fishes, though this does not seem to hold in some known instances. Interactions of the second type do not seem to be directly related to resource availability. There are biological and statistical reasons why the likelihood of finding such interactions will be positively correlated with the supply of recruits. The general significance of these interactions for the structure of reef fish assemblages will depend on (1) the level of larval supply, and (2) the number and abundance of species that show this kind of behavior.
Carbon Dynamics of Rocky Mountain Douglas‐Fir: Influence of Water and Nutrient Availability
Authors: Gower Stith T. , Vogt Kristiina A. , Grier Charles C.
Published: April 2006

Changes in biomass distribution, canopy dynamics, and above— and belowground net primary production were examined in a Rocky Mountain Douglas—fir (Pseudotsuga menziesii var. glauca forest in New Mexico. Nutrient and water availability were experimentally altered by: fertilization (F), irrigation (I), carbon in the form of wood chips (WC), carbon + irrigation (WC/I), and control (C). Prior to treatment, aboveground tree biomass ranged from 238 to 369 000 kg/ha, projected leaf area index (LAI) ranged from 5.4 to 8.7 m2/m2 and aboveground net primary production (ANPP) ranged from 9200 to 11 900 kg · ha—1 · yr—1. Aboveground NPP was correlated positively (R2 = 0.85) with LAI before the treatments. Canopy dynamics were strongly influenced by water and nutrient availability. For trees of similar diameter, irrigated and fertilized trees supported a significantly greater biomass of new twig and new foliage than control trees. During the 2—yr study leaf area index (LAI) increased by 5, 12, 18, and 24% in the C, I, WC/I, and F plots, respectively, and decreased by 3% in the WC plots. Stand level biomass distribution and production patterns were also affected by the availability of nutrients and water. Two years after the treatments were initiated, new foliage masses were 2400 (F), 2300 (WC/I), 2000 (I), 1900 (C), and 1800 (WC) kg/ha. In 1986, aboveground NPP was 33% greater in the F than WC treatment. Irrigation also increased ANPP. Fine root net primary production ranged from 1540 to 4200 kg · ha—1 · yr—1 and was significantly greater (P < .1) in the control than in the four treatments. BNPP comprised 46 (C), 32 (WC), 31 (I), 23 (WC/I), and 23 (F) % of total NPP. Total NPP was correlated positively with LAI (R2 = 0.66) and ranged from 15 360 kg · ha—1 · yr—1 in the WC treatment to 21 140 kg · ha—1 · yr—1 in the F treatment. Many of the physiological relations between water or nutrient availability and production and carbon allocation reported in this study are consistent with results from studies on lowland Douglas—fir and other conifer forests in the Pacific Northwest. Collectively, these studies provide a mechanistic understanding of how water and nutrient availability govern production and carbon allocation of conifer forests in the western United States.
Population Cycles of Mammals: Evidence for a Ratio‐Dependent Predation Hypothesis
Authors: Akcakaya H. Resit
Published: April 2006

Populations of certain mammal species and their predators show cyclic fluctuations in northern latitudes, and the amplitude of cycles in some cases increases towards the north. The evidence reviewed suggests that (1) abiotic factors and intrinsic mechanisms are unable to explain cycles; (2) quantity and quality of food resources of the herbivore population have important effects on population dynamics, although plant—herbivore interaction cannot explain the cycles by itself; (3) predation is another important factor for these populations, and probably essential for cyclicity of herbivore populations. A number of mathematical models have shown that prey—predator models can produce limit cycles, but they have not demonstrated that the cyclic fluctuations observed in natural populations can be explained by the mechanisms they incorporate and the parameters they define. In this study a mathematical model is developed to predict specific patterns of prey—predator cycles observed in nature with independently estimated parameters. This prey—predator model is based on the concept of "ratio dependence": the trophic functions (functional and numerical responses) are modeled as functions of prey—to—predator ratio rather than as functions of prey density only, as in traditional prey—predator models. This approach incorporates the concept of interference in a simple way by describing trophic interactions as functions of per capita resources. The parameters of the model are estimated from studies on the biology of cyclic lynx and hare populations, rather than by fitting timeseries data to the model. Parameters of the model give rise to limit cycles when they are changed in the way they are expected to change from south to north, which is consistent with the observations on the latitudinal patterns in cyclicity. The major quantitative prediction of the model is the cycle period. The period is predicted to be around 10 yr, which is the observed period of hare—lynx fluctuations.
A Contribution to the Theory of Competing Predators
Authors: Hsu S. B. , Hubbell S. P. , Waltman Paul
Published: April 2006

This paper concerns the growth of 2 predator species competing exploitatively for the same prey population. The prey population grows logistically in the absence of predation, and the predators feed on the prey with a saturating functional response to prey density. Specifically, we assume that Michaelis—Menten kinetics or the Holling "disc" model describe how feeding rates and birth rates change with increasing prey density. We focus on the question of which predator species will survive and which will not, given the growth parameters of the prey and the functional response parameters of the 2 predators. Which predator wins or loses depends critically on the relative magnitude of the prey carrying capacity, K, and the λ parameters of the 2 predators. °i represents the prey density at which the ith predator "breaks even" (equal birth and death rates). This prey density is defined by the product of the predator's half—saturation (Michaelis—Menten) constant times the ratio of the predator's death rate to its intrinsic rate of increase. Coexistence is also possible for a wide range of parameters, but only as a periodic solution. A primary conclusion is that coexistence is possible only if the predator with the smaller half—saturation constant also has the smaller birth—rate—to—death—rate ratio. This necessary constraint is the mechanistic equivalent to requiring that 1 predator be an "r—strategist" and the other be a "K—strategist." This condition is insufficient to guarantee coexistence, however. If the prey carrying capacity, K, is "too small" the K—strategist wins, and if K is "too large," the r—strategist wins. The bounded region of intermediate K values permitting coexistence is defined by the functional response parameters of the 2 predator species. The greater the disparity between the half—saturation constants of the 2 predators, the larger the region of K permitting coexistence.
Adult Body Mass and Annual Production/Biomass Relationships of Field Populations
Authors: Banse Karl , Mosher Steven
Published: April 2006

We investigate specific production rates (per unit biomass) of populations using published data on the relation of annual production/mean biomass (P/B). Aquatic and terrestrial invertebrates between the sizes of copepods and clams are emphasized, ranging about 105—fold in body mass upon reaching maturity (Ms, in kcal to compare with respiratory energy expense) and about 102—fold in P/B. Fishes and mammals are briefly treated; phytoplankton is mentioned. For 33 invertebrates living at annual mean temperatures between about 5° and 20°C, Ms is shown to be an efficient and precise estimator, or scaling factor, of the annual P/B. The rate declines markedly with Ms according to P/B = 0.65Ms—0.37. The exponent differs significantly from the —0.25 power of comparative physiology. Most of the measured values of P/B fall within 50 to 200% of predicted values. Much of this variability is associated with the ratio of annual production/annual respiration (P/R): for a given Ms, species achieving about half the predicted P/B have P/R ratios of about 0.1; those achieving twice the predicted P/B have P/R ratios of about 1.0. Age upon reaching maturity contributes some variability, with late—maturing (>1 yr) species tending towards a higher P/B. The variability is not significantly correlated with phylogenetic relationships (excepting insects for which P/B might not be mass—dependent), trophic type, major habitat, production rate, or biomass of the populations. The values of P/B of invertebrates living at annual mean temperatures >25° may be elevated over those of temperate species of the same Ms, while those of polar forms are depressed. The reasons for a single power function governing the mass dependence of P/B of temperate invertebrates, and for the particular exponent, are unclear; an ecological cause, i.e., mortality, combining with the general size dependence of life processes, is implicated. On the average, the annual specific mortality rate equals P/B and hence also declines by 0.65Ms—0.37. Very small metazoans (pelagic rotifers, benthic meiofauna) tend to have an appreciably lower P/B than indicated by the relationship for larger invertebrates. A refuge from predation by being small is postulated which may also apply for phytoplankton. For meiofauna, a power function of mass dependence of P/B with average rates 3—5 times below those of the larger invertebrates is suggested. Annual P/B values of fishes and mammals likewise decline by a power function of Ms; the few available data yield exponents of —0.26 and —0.33, respectively. Ecological reasons are again invoked. Values of P/B and the specific mortality rates of temperate fishes seem to be 4—5 times, and those of mammals 20—25 times, higher than those of temperate invertebrates of the same mass.
Structure and Function of Two Antarctic Terrestrial Moss Communities
Authors: Davis R. C.
Published: April 2006

Two bryophyte—dominated communities in the maritime Antarctic are analyzed in terms of the transfer and standing crops of organic matter within them. A moss turf dominated by Polytrichum alpestre and Chorisodontium aciphyllum and a moss carpet composed of Calliergon sarmentosum, Calliergidium austro—stramineum, and Drepanocladus uncinatus with the liverwort Cephaloziella varians were investigated at Signy Island, South Orkney Islands. Biomass, respiration, and production data for the primary producers (mosses, lichens, liverworts, and algae), for the fauna (Protozoa, Rotifera, Tardigrada, Nematoda, Acari, and Collembola), and for the microflora were synthesized, and annual rates of consumption, egestion, assimilation, and production were derived. The two communities showed similar levels of productivity, trophic structure, and efficiencies of organic matter transfer, but different Collembola and Acari standing crops, turnover of mosses, and accumulation of dead organic matter. These features are discussed in relation to the role of biotic and abiotic variables in determining community structure and function.
The Influence of Food Habits on the Energetics of Eutherian Mammals
Authors: McNab Brian K.
Published: April 2006

The level of energy expenditure in eutherian mammals is correlated with the type of food consumed, especially in medium—sized to large species; some foods (including vertebrates, herbs, and nuts) permit high basal rates, while other foods (including invertebrates, fruit, and the leaves of woody plants) require low basal rates. Various properties of a food, including a low digestibility, a high content of plant secondary compounds, the inability to separate food from non—nutritive particles, and a seasonal reduction in availability, may require a consumer to have a low basal rate of metabolism; all of these factors are exaggerated in importance by the high food intake of large mammals. In small species most foods, except flying insects and seed crops in the desert, permit high basal rates and effective endothermy. Climatic factors modify these relationships to a limited extent, while a specialization in moderately—sized species to arboreal habits leads to reduced activity, smaller muscle mass, and lower basal rate than is found in terrestrial species using the same food resources. Mixed diets generally produce basal rates intermediate to those expected from the component specialist diets. The correlation of basal rate with food habits has the following demonstrable consequences for mammals. (1) The scaling of basal rate usually follows the Kleiber relation, unless food habits require low basal rates, or temperature regulation requires high rates. (2) Mammals that feed on foods associated with high basal rates have a higher reproductive output than mammals of similar size that use foods requiring low basal rates. (3) Predator avoidance is correlated with level of energy expenditure and food habits, terrestrial species with low rates of metabolism relying principally on burrows or passive integumental structures, such as shells, plates, or spines. (4) Most living "conservative" mammals use foods that require low basal rates of metabolism, a condition that protects conservative species from replacement by "advanced" eutherians, which are also required by these foods to have low basal rates.