bluuebunny/crossref_metadata_2025 huggingface dataset:
Consequences of Flowering‐Time Variation in a Desert Annual: Adaptation and History
Authors: Fox Gordon A.
Published: May 2006

Can observed life histories be successfully explained in terms of their current adaptive significance, or do we need historical data as well? This issue is examined for the case of the desert annual Eriogonum abertianum Torr. (Polygonaceae). Individuals of this species flower in the spring, or following the onset of summer rains, or both. In order to estimate survivorship probabilities and fecundities, large samples of marked plants were followed in each of two years at two sites. In both years the Sonoran Desert (lower summer rainfall, hotter) population experienced significantly more mortality during the foresummer droughts, and had a significantly greater proportion of spring—flowering plants, than the Chihuahuan Desert (greater summer rainfall, cooler) population. This result was reproduced in a greenhouse study (Fox 1989). The model of selection comparing the spring—plus—summer flowering habit with spring—only flowering suggests that, in the years studies, expected summer fecundity may not have offset the risk of foresummer mortality in the Sonoran Desert population. Distributional data indicate that, rather than switching to a spring—only phenology as predicted by the model, the species' range ends where summer rainfall declines abruptly. Fossil and biogeographic evidence lend support to an adaptive interpretation of earlier flowering in the Sonoran Desert: They suggest a mainly summer—flowering origin for the species and an invasion of the Sonoran Desert during a period with greater summer rainfall than is the case at the present. However, the persistence of the spring—plus—summer habit is not explained by either the demographic or the historical data.
Seedling Growth, Physiology, and Survivorship in a Subalpine, Volcanic Environment
Authors: Chapin David M. , Bliss L. C.
Published: May 2006

The relationship of seedling survivorship to specific physiological or morphological traits is usually only inferred in demographic studies. We compared seedling survivorship, growth, morphology, and water relations of two subalpine herbs (Eriogonum pyrolifolium and Polygonum newberryi) on Mount St. Helens in order to examine the relationship between population and functional biology more directly. Survivorship of two cohorts of seedlings (1982 and 1983) was followed through 4 and 3 yr, respectively. Seedling growth was measured in two substrate types (pre—eruption soil and 1980 deposited tephra) and under different levels of nutrients and water under controlled environmental conditions. Water relations parameters of the two species were determined in conjunction with the laboratory growth experiment. The 1982 cohort of Eriogonum had a significantly higher rate of survival than did that of Polygonum over four growing seasons, while the 1983 cohort did not differ in survival over three growing seasons. Survival rates were closely related to the amount of rainfall, with Eriogonum having significantly higher survival during dry periods than Polygonum. Growth of both species was greater in pre—eruption soil than in 1980 deposited tephra; the difference was much more pronounced in Polygonum. Growth of Eriogonum seedlings was also less sensitive to lower nutrient and water availability in the laboratory experiment than growth of Polygonum. Eriogonum had lower osmotic potentials, higher stomatal conductance, greater fine root biomass, and lower intrinsic growth rate than did Polygonum. These appear to be important characteristics contributing to greater stress tolerance and higher seedling survivorship in Eriogonum.
Resistance of the Microbial Community within Salt Marsh Soils to Selected Perturbations
Authors: Christian R. R. , Bancroft K. , Wiebe W. J.
Published: May 2006

The response of the soil microbial community in a short Spartina alterniflora salt marsh to selected, long term perturbations was examined. Alternative hypotheses of linkage between macrophyte production and the microbial community biomass and activity were tested. In 2 perturbation experiments macrophytic primary production was removed from marsh plots by clipping shoots and printing beneath ground parts for periods up 10 18 mo. In a third experiment monthly enrichments of glucose, ammonium nitrate and their combination were made for 5 mo to both clipped and pruned plots as well as unclipped control plots. The state of the microbial community was monitored by adenosine triphosphate and total adenylate concentration, community adenylate energy charge ratio and anaerobic uptake of 14C—glucose by mud slurries. The overall responses of the various parameters were consistent with the hypothesis that the soil microbial community is relatively unlinked to plant growth. This "unlinking" appears responsible for the observed resistance to change by the microbial community in the face of perturbations to the marsh system. Two mechanisms of resistance were postulated. First, while the microbial community resides in a large reservoir of organic matter, most of this organic matter may be relatively refractory. Hence, the microorganisms would be nutrient limited by the slow transformation of this material. Such a large resource pool with a long turnover time would promote resistance to perturbations that alter plant productivity. Second, the microbial community would be resistant to changes rather than nutrient status if in fact it were limited by physiochemical, spatial constraints rather than nutrients. While neither hypothesis could be totally rejected, our results give greater support to the second hypothesis.
Genetic Differentiation of Douglas‐Fir Populations from the Northern Rocky Mountains
Authors: Rehfeldt Gerald E.
Published: May 2006

Growth potential, phenology, and cold hardiness were compared in progenies of 5 trees from each of 18 populations of Douglas—fir (Pseudotsuga menziesii va. glauca). Five—year—old seedlings growing in 2 nursery environments allowed assessment of population differentiation according to 6 variables related to growth and phenology. Freezing tests provided 5 variables that expressed cold hardiness in mid—September and near maximal hardiness. Statistical analyses of 11 variables suggested a differentiation of populations into 3 provinces. One province included cool environments, regardless of geographic origin. The remaining 2 provinces included relatively warm environments from either western Montana or eastern Washington and northern Idaho. Variation among provinces, among populations within provinces, and among trees within populations contributed to the genetic variance.
Influence of Male and Female Quality on Clutch Size in Tits (Parus Spp.)
Authors: Slagsvold Tore , Lifjeld Jan T.
Published: May 2006

Field experiments were designed to examine the effects of parental ability on clutch size, for the two sexes separately. To handicap parental ability we removed feathers from the wings and the tail of three tit species (Parus spp.) during the initial incubation period. We then removed their first clutches, and examined the effect of the handicap on the subsequent nesting. In Blue Tits (P. caeruleus), and Coal Tits (P. ater), handicapped females reduced the size of the repeat clutch more than control females. In Blue Tits handicapped females fed their young at a lower rate, lost more body mass during the nestling period, and at fledging time their broods were significantly smaller than those of controls. Their fledglings had a body mass, similar to the control fledglings. Handicapped female Great Tits (P. major) only reduced their clutch size a small amount; consequently, at fledging time, their body mass and those of their young were lower than for controls. The males of the three species of tits did not seem to increase parental investment when their mate was handicapped. When male Blue and Coal Tits were handicapped their mates did not reduce clutch size more than did those of the control group, despite a reduction in parental investment by handicapped males. However, breeding success was not significantly affected by handicapping males. We conclude that the clutch size determination of female tits is primarily based on their own ability to feed their young, and not on the quality of their mate. Male tits seem to have a lesser influence on breeding success than females, and males seem less willing or less able to increase their parental investment.
Dispersal Adaptations of Some Acacia Species in the Australian Arid Zone
Authors: Davidson D. W. , Morton S. R.
Published: May 2006

Most Australian representatives of the genus Acacia have diaspores with arillate appendages indicative of adaptation for active dispersal by animals. Based on physical and chemical characteristics of these arils and mechanisms of diaspore presentation, a number of arid zone acacias can be distinguished as probable ornithochores, myrmecochores, or species lacking active dispersal by animals. Two factors suggest that dispersal adaptations are evolutionarily labile in the face of changing selection pressures. Both myrmecochores and ornithochores are prevalent in each of the three largest taxonomic sections of the Australian subgenus Phyllodineae. Second, diaspores of at least one species, Acacia ligulata, exhibit geographic variation, resembling those of myrmecochores in one population and ornithochores in a second population. The colorful lipid—rich arils of avian—dispersed species are nutritionally more valuable than the relatively small, white appendages of ant—dispersed species with similar—sized propagules. While ants often collect the diaspores of ornithochorous acacias, we have no evidence that birds use the arils of myrmecochores. Patterns of seedling establishment on ant mounds, and under the canopies of trees where birds perch and defecate, are consistent with these observations. Exploitation of diaspores by birds may help to reduce the destruction of seeds by parasitoids and, in part, compensate for the higher aril expenditures (per milligram of propagule) in avian—dispersed species. Dispersal of seeds by both ants and birds directs seeds to microhabitats where nutrients are concentrated and water resources are more plentiful and/or are used more efficiently. Similarities between mound and subcanopy microhabitats may have facilitate evolutionary transitions between myrmecochory and ornithochory. The nutrient poverty that generally characterizes Australian soils has possibly played a role in selecting for seed dispersal by ants and birds in this genus as well as in many other Australian plants.
Variation in Cold‐Hardiness of Fraxinus Americana Stem Tissue According to Geographic Origin
Authors: Alexander Nancy L. , Flint Harrison L. , Hammer P. Allen
Published: May 2006

Cold—hardiness of stem sections of white ash (Fraxinus americana L.) from 10 geographic origins in eastern North America, growth in a provenance planting in south Michigan, was determined by controlled freezing. Northern plants were more cold—hardy than southern plants in early and midwinter, but differences disappeared by early spring. Substantial variation in cold—hardiness was found among trees within each origin. Multiple regression of killing temperatures on latitude, longitude, elevation, average annual minimum temperature, and annual frost—free period proved useful in predicting cold—hardiness, and may be useful in forecasting performance of trees in locations removed from their sites of origin.
Mutual Predation in Assembled Communities of Odonate Species
Authors: Robinson James V. , Wellborn Gary A.
Published: May 2006

Larval individuals from six anisopteran species were added to artificial ponds so that each pond contained an equal number and size distribution of each species. Half of these ponds were exposed to an additional anisopteran, Anax junius. Interodonate predation in Anax—free ponds was size dependent, with the smallest species, Perithemis tenera, experiencing the highest mortality. Predation in ponds containing Anax was not size dependent, but was species dependent. Plathemis lydia individuals were not significantly affected by Anax, probably due to the tendency of Plathemis to dig deeply into the sediment. Pe. tenera was shown to have a different allometric relationship between head width and body volume than the other six dragonfly species. We postulate that this is correlated with its small size and is an adaptation to increase the range of prey available to it.
Seasonal Energy, Water, and Food Consumption of Negev Chukars and Sand Partridges
Authors: Kam Michael , Degen A. Allan , Nagy Kenneth A.
Published: May 2006

Chukars (Alectoris chukar) and Sand Partridges (Ammoperdix heyi), two ground—dwelling phasianids, are permanent residents of the Negev desert and are sympatric over much of their ranges. Sand Partridges (body mass = 150—250 g), however, inhabit only arid and very arid areas, whereas Chukars (mb = 350—600 g) are widely distributed and inhabit deserts only at the margins of their ranges. We compared some of the desert adaptations of these phasianids by measuring the seasonal field metabolic rates (FMR) and water influxes (using doubly labelled water), diet selection, and food requirements of free—living Chukars and Sand Partridges at a site where both species occurred. Both species showed adaptation in the form of low energy metabolism, which ranged from 43 to 81% of that expected for birds of similar body mass. During summer, Sand Partridges had lower energy expenditures (5.47 kJ°g—0.61°d—1) and water influxes 72.3 mL°kg—0.75°d—1) than did Chukars (6.42 kJ°g—0.61°d—1 and 93.5 mL°kg—0.75°d—1, respectively), indicating more pronounced adjustments to arid conditions in the desert specialist. However, both species obtained more than half of their water influx in summer by drinking. Their summer diet was relatively dry, consisting mainly of seeds (80%) along with some green vegetation (18%) and, in Chukars, occasional arthropods. This situation changed abruptly after winter rains, which induced germination and reduced the availability of seeds. Chukars were unable to maintain energy balance in the face of low ambient temperatures and a diet (90% green vegetation) that contained much water but comparatively little energy, and they mobilized fat reserves to meet energy requirements. Most Sand Partridges left the study area after winter rains, apparently migrating to the lower elevation, warmer, and drier Arava (part of the Rift Valley). The winter rainy season appears to be the most stressful time of the year for both species. The adaptations to hot, dry conditions possessed by Sand Partridges may be accompanied by constraints on their abilities to cope with cool, wet conditions, and this may restrict them to arid and very arid habitats.
Nutrient‐Use Efficiency of Woody Plants on Contrasting Soils in the Western Great Basin, Nevada
Authors: Schlesinger William H. , DeLucia Evan H. , Billings W. D.
Published: May 2006

Soils that develop on areas of hydrothermally altered rock in the western Great Basin of Nevada support Sierran conifers, such as Pinus ponderosa, in a desert climate. These soils have low pH (°3.7) and low concentrations of HCO3——extractable P (5.6 mg/g), compared to adjacent brown desert soils supporting sagebrush (Artemisia tridentata) vegetation. The occurrence of Sierran conifers appears to be related to their tolerance of the unusual soil chemistry, high nutrient—use efficiency in growth, high reabsorption of foliar nutrients before leaf abscission, and slow growth rates. Most of these traits appear to be inherent characteristics of evergreen vegetation, and show little acclimation to the nutrient—poor conditions on hydrothermally altered rock. In contrast, plants of the Great Basin sagebrush vegetation are physiologically intolerant of the unusually soils that develop from hydrothermally altered rock and are excluded from such sites.
Functional Response and Success in Juvenile Mantids
Authors: Hurd L. E. , Rathet Ilyse H.
Published: May 2006

First—instar mantid nymphs (Tenodera sinensis) of a single cohort exhibited a Holling's Type II functional response to prey density in the laboratory. However, functional response was a poor indicator of success. Predation rate increased well beyond maximum gain in survival, development time, and size at ecdysis, all of which are directly related to fitness in this species. Food limitation is common for this species in nature, particularly during the first instar, and apparently selection has not been adequate to optimize predation rate. Predation rate varied over time as well as with density. Daily feeding rate among nymphs fed ad libitum reached a peak midway through the instar, and then dropped sharply just prior to ecdysis. These and other sources of variability will influence and impact of these generalist predators on arthropod assemblages in the field.
The Population Biology of Dugesia Tigrina (Platyhelminthes: Turbellaria) in a Thermally Enriched Alberta, Canada Lake
Authors: Folsom Todd C. , Clifford Hugh F.
Published: May 2006

The triclad flatworm Dugesia tigrina (Girard) is abundant in Lake Wabamum, a west—central Alberta lake receiving thermal effluent. A 14—month study was carried out to investigate D. tigrina's population ecology and the effect a thermally altered environment might have on Dugesia. Our data support the hypothesis that D. tigrina is limited by intraspecific competition for food during and after reproduction. In spring, both the normal water and heated water triclad populations grew rapidly and produced cocoons. Recruitment of young intensified food competition, causing shrinkage and mortality. The spring gain in length and weight was lost through shrinkage of individuals, and numbers of triclads in autumn were similar to prebreeding numbers. Hence the hypothesis is supported for populations in the thermally altered and the normal lake habitats. Triclads from the thermally enriched environment were found to be 2x as fecund as normal lake triclads. Cocoon production was probably increased to some extent by thermal effluent. However, the elevated mortality rate caused by the mechanical harvesting of abundant macrophyte populations in the warm water area, estimated at 1—3x the standing crop of triclads, probably accounts for much of the increased fecundity.
Significance of Litter Size in Musculium Securis (Bivalvia: Sphaeriidae)
Authors: Mackie G. L. , Qadri S. U. , Reed R. M.
Published: May 2006

Experiments were carried out to determine the effects of population density on the natality of Musculium securis (Prime). Laboratory studies showed that: (1) total recruitment increased with increasing densities of parental stock, to an asymptotic value, (2) that recruitment was greater than the reproductive carrying capacity, and (3) that the total litter size per average reproductive adult decrease with increasing densities of parental stock, to an asymptotic value. It is suggested that surplus recruitment may be an important mechanism in population control. Field studies supported these findings and showed that interspecific competition between Musculium securis and Musculium transversum resulted in lower natalities for both species. Also, competition among individuals of the predominant species is primarily intraspecific and the presence of the subdominant species has little effect on their reproductive capacities. Temporary coexistence is possible for the 2 species but Musculium transversum has a higher natality and probably would eventually exclude Musculium securis when they were complete competitors.
Detecting Changes in Ecological Time Series
Authors: Jassby Alan D. , Powell Thomas M.
Published: May 2006

Some practical techniques are discussed for analyzing time series whose statistical properties are changing with time. We first consider how principal component analysis can reduce the multidimensional nature of certain series and, in particular, apply this technique to the analysis of changing seasonal patterns. Discussions of trend, changes in oscillatory behavior, and unusual events follow. The problem of making inferences regarding causation is briefly considered. We conclude with a call for flexibility in approach.
Comparison of Temporal and Spatial Variation in the Zooplankton of a Lake by Means of Variance Components
Authors: Lewis William M.
Published: May 2006

A standard 2—way analysis of variance is used to separate components of variance in zooplankton abundance data (individuals per unit area). The sampling design and interpretation, which are applied to Lake Lanao, Philippines, require that samples be (1) widely distributed over the limnetic zone, (2) representative of the full range of temporal variation, and (3) free of significant autocorrelation. Under these conditions the relative importance of spatial and temporal variation can be quantitatively compared for individual zooplankton species and developmental stages. The analysis yields variance components associated with (1) stations, (2) dates, (3), station—date interaction, and (4) error. The station component is interpreted as a quantitative measure of "fixed" spatial patchiness, which is caused by temporally stable differences between stations. The dates component is a quantitative measure of the variation in abundance through time, and the interaction component is a quantitative measure of "emphemeral" spatial patchiness. Ratios between these variance components provide a measure of their relative importance. The analysis shows that, among 16 zooplankton species and developmental stages, (1) there are radical differences between species in the relative importance of spatial and temporal variation, (2) the 2 spatial components of variance (fixed plus ephemeral) exceed the temporal component of variance for about half the species, (3) the ephemeral component of spatial variance is typically much greater than the fixed component of spatial variance,and (4) the spatial component of variance has a much greater relative importance in the large cladoceran species than in other zooplankton species. Interspecific differences in the relative importance of spatial and temporal patchiness may be related to differences between species in adaptive strategies for survival in the limnetic zone.
Resource Utilization by Desert Rodents in the Lower Sonoran Desert
Authors: Stamp Nancy E. , Ohmart Robert D.
Published: May 2006

Four species of heteromyid rodents were studied in 5 communities in the Lower Sonoran Desert to examine differences in resource utilization by heteromyids in terms of: (1) collection of seed species, seed size and seed type (shrub—tree, forb and grass) and (2) association with amount of perennial cover of habitat. These rodents were not allocating resources by seed species or seed size. These rodents were collecting seeds to some degree by seed type, however, this was related to foraging in particular microhabitats. We found no correlation between numbers of each species of seed in cheek pouch contents and energy content per seed species. These heteromyids were opportunistic in collecting seeds as shown by considerable variation in seed species collected by populations and species among habitatas and seasonal variation in seed species collected. These heteromyids appear to partition seed resources by specializing on particular microhabitats. If these heteromyids use microhabitats optimally as granivores, they cannot allocate resources by seed species, size or type without risking local extinction due to the high variable production of specific seed species and sizes in the desert. The regular distribution of body sizes among heteromyids in a community appears to be a consequence of exploiting particular microhabitats in the desert community rather than allocating resources by seed—size selection.
Foraging Strategies of American Kestrels During Breeding
Authors: Rudolph Seri G.
Published: May 2006

Of the two hunting methods most commonly used by American Kestrels (Falco sparverius), hovering cost more but yielded more per unit time perch—hunting. Birds increased their use of hovering relative to other hunting methods as wind speed increased (lowering the energetic cost of hovering flight), and as the number and size of their dependents rose. Perch—hunting kestrels left a foraging site shortly after reward rate fell below the average reward rate for all sites, a behavior consistent with maximizing net energy intake when travel costs are considered. Larger prey were preferentially transported to the mate or young, as predicted by central place foraging models. In three pairs, males provides females during egg—laying, incubation, and brooding, but one pair foraged individually and shared incubation. Each pair foraged in ways that minimized the costs of energy acquisition in its particular situation.
Clutch Size, Nest Size, and Hatching Asynchrony in Birds: Experiments with the Fieldfare (Turdus Pilaris)
Authors: Slagsvold Tore
Published: May 2006

Breeding strategy of an open—nesting passerine bird, the Fieldfare (Turdus pilaris) was studied in a woodland in Norway during four successive breeding seasons. Most birds laid clutches of five or six eggs; only 1% laid more than six. For 100 nests, eggs and/or chicks were added to raise the final number to seven hatchlings. Parents that laid a clutch of five eggs showed a equal skill in raising broods of seven, as did those who laid six. In enlarged broods, when only small age differences existed among the hatchlings, their survival rate was higher than that of enlarged asynchronous broods. In the enlarged synchronous broods the nestlings the subsequently died did so at a greater age than did those in the asynchronous broods. Brood size frequency for synchronous broods, recorded 8 d after brood enlargement, deviated from that expected under a random mortality pattern, i.e., mortality more resembled in "all—or—one" type. Hatching success was not lower for larger clutches (provided that the eggs hatched synchronously); the parents showed great skill in raising enlarged broods, and these nests were not subjected to a much greater degree of predation than were nests that contained small clutches and broods. The Fieldfare therefore normally rears a smaller—sized brood than could be nourished. More pairs that were provided with an artificial, large—sized nest managed to raise a brood of seven than did pairs that attempted to rear seven in their own original nest. Brood reduction in birds may not be adaptive, as argued by Lack and others, but may result from overcrowding. The reason why wider nest cups are not built in nature may be related to problems involved in hatching the eggs successfully; hatching losses were greater in enlarged nests than in natural nests.
Energy Trade‐Offs and Foraging Mode Choice in American Eels
Authors: Helfman Gene S. , Winkelman Dana L.
Published: May 2006

American eels (Anguilla rostrata) use three different models when handling food: suction, shaking, and spinning (rotational feeding). We investigated mode selection and mode switching during foraging in terms of relative costs and benefits of different modes. Eels were fed food items that differed in size and consistency, thereby inducing particular modes. To test the hypothesis that American eels forage efficiently by selecting foraging models that maximize net energy intake and growth, we determined whether modes differed in short—term energy costs and long—term effects on growth rate, and whether eels preferred food types that maximize short— and long—term net benefits. Net energy intake (energy ingested — energy consumption represented by oxygen uptake) was greatest when suction was the chief mode employed, and was reduced during shaking and spinning. Animals using spinning fed the slowest and ate relatively little food. Eels fed a diet that required them to feed by only spinning or shaking lost mass faster than eels allowed to feed by suction. When given a choice of food types, eels preferred energetically efficient types (suction over both shaking and spinning, shaking over spinning). Our results suggest that rotational feeding is an alternative foraging mode that facilitates dismembering of large food items, but this benefit can be compromised by energy and time costs. Spinning is the least preferred mode and is used when other modes are ineffective. Mode switching in this species can be considered optimal in that mode choice and switching appear to maximize net energy intake in a manner that directly affects growth rate and, presumably, fitness.
Rodent Occurrence, Habitat Disturbance, and Seed Fall in a Larch‐Fir Forest
Authors: Halvorson Curtis H.
Published: May 2006

Small—mammal population changes were measured for 5 yr (1970—1974) by live trapping on broadcast burned western larch (Larix occidentalis)/Douglas—fir (Pseudotsuga menzielsii) clear—cuts and in uncut timber on a north and a south slope in western Montana. Four species comprised 96% of the 1324 animals caught: deer mice (Peromyscus maniculatus) 42%, red—backed voles (Clethrionomys gapperi) 27%, red—tailed chipmunks (Eutamias ruficaudus) 22%, and long—tailed voles (Microtus longicaudus) 5%. Deer mice and chipmunks were common on clear—cut and timber plots. The red—backed vole and long—tailed voles were associated with moist sites but showed local allopatry. The red—backed voles were present only under tree canopy and the long—tailed vole was found only in absence of tree canopy. A hard burn effect was to eliminate most of the organic mantle and all small mammals except deer mice, who existed as the single species for 2 yr, and as 80—90% of numbers for 5 postburn yr. A light burn which left duff intact was associated with retention of species diversity and a low initial postburn (2 yr) mammal population, followed by the largest increases. Numbers of deer mice varied inversely with numbers of red—backed voles in the timber. Deer mice increased sharply on all plots the first fall after a heavy conifer seed crop, an occurrence reported by other workers. From these pattern observations it is theorized that red—backed voles may dominate deer mice, but a heavy seed crop can temporarily enhance competitive standing of deer mice. An open, xeric, pioneering situation (hard burn) was conducive to persistently high deer mouse populations. The most obvious habitat feature associated with an inverse spatial relationship between the two voles was tree canopy. The long—tailed vole may be further discriminated against by drier habitats. Clear—cutting appeared to be the principal determinant of total population size, but burn intensity seemed to influence species composition.
Cu and Zn Kinetics in Myriophyllum Heterophyllum Michx. and Potamogeton Richardsonii (Ar. Benn.) Rydb.
Authors: Cushing C. E. , Thomas J. M.
Published: May 2006

Two macrophytes, Myriophyllum heterophyllum and Potamogeton richardsonii, and sediments were transplanted (1) from a site with low trace metal concentrations in the sediments to one with higher level, and (2) from the site with high concentrations to artificial ponds containing sediments with lower concentrations to assess the uptake and retention processes for Cu and Zn. Uptake of Cu and Zn by the sediments was extremely slow over the 100—d study; only the slope of the uptake of Zn in the upper 5 cm was significantly >0(P <.01). Nonlinear least squares fits of P. richardsonil and M. heteophyllum data to mathematical models revealed that predicted concentrations and measured uptake values were in good agreement. Uptake and retention half—times averaged 3.7 and 6.7 d, respectively, and showed little difference between plant species of trace metals. Calculated ratios lead us to speculate that known levels of Cu and Zn in one plant species may be useful in estimating concentrations in the other. The data suggest that roots, rather than shoots, are the predominant site of uptake for Cu and Zn in these species.
Population Ecology of Rattus Rattus Across a Desert‐Montane Forest Gradient in the Galapagos Islands
Authors: Clark David B.
Published: May 2006

Populations of introduced black rats (Rattus rattus) were studied by removal trapping in five nonagricultural habitats in the Galapagos Islands; montane forest, montane scrub, tropical deciduous woodland, thorn scrub, and savannah. Density of rats ranged from 0.4 to 18.9/ha, and both density and biomass of rats were significantly correlated with an index of vegetation biomass. The estimated quantity of vegetation per individual and per unit biomass decreased with increasing rat density. These results suggest that rat poplations were food—limited. A 2—mo drought significantly lowered condition (mass/length) of montane forest and montane scrub rats. Analysis of size and reproductive classification of resident and immigrant rats showed significant heterogeneity among subgroups bases on sex and period of capture. Rats from the two habitats of lowest rat density appeared to have more specific microhabitat requirements than rats from denser populations. Breeding was confined to the hot and early cool seasons (January through July) in all habitats. Mean and minimum body lengths in all populations were positively correlated with time since arrival of arid zone rains, while the coefficients of variation of these quantities were negatively correlated. Sex ratio varied seasonally; the percentage of males increased significantly during the nonbreeding season. Intraisland pelage differentiation was observed. Compared to other tropical rodents, Galapagos Rattus rattus have been very successful in range of habitats occupied and in biomass maintained.
Phosphate Mining Induced Vegetation Changes on Nauru Island
Authors: Manner Harley I. , Thaman Randolph R. , Hassall David C.
Published: May 2006

Postmining succession and pre—mining forest vegetation were studied on the isolated, tropical, central—Pacific, phosphate—rich island of Nauru. An analysis was made of the extent to which natural vegetation has been reestablished on the highly disturbed open—pit phosphate—mined areas that constitute some three—quarters of this 22—km2 island. Sixty—four sample quadrats were taken from the successional range of revegetated mined areas and from the unmined plateau forest. Frequency and percent cover were obtained for all species to determine their ability to colonize different microhabitats in the mined area. A complete inventory was also made of all plant species present on Nauru, to identify the pool of potential recolonizers of the mined area. Of the 467 plant species found on Nauru, 47 native and 79 introduced weed species are potential short— and long—term colonizers. We found 50 of these 126 potential colonizers in the 64 sample quadrats. Highly dispersible, exotic weed species predominate in primary succession, but they are rapidly replaced by native plants such as Dodonea viscosa and Ficus prolixa, and by pantropical strand plants such as Scaevola taccada, Morinda citrifolia, Premna obtusifolia, Guettarda speciosa, and Calophyllum inophyllum. These species are scattered and stunted, however, when compared to their growth habitat in the unmined forest. The resultant succession seems to be progressing very slowly in the highly disturbed habitats. Centuries will be needed for the forest to reestablish naturally, even in a modified form, and most likely the forest will be composed primarily of Calophyllum inophyllum and other native coastal strand trees as dominants, with Ficus prolixa on the exposed coral—limestone pinnacles that remain after mining. If, however, the landscape is artificially modified by leveling the pinnacles and filling in the pit bottoms, and if suitable exotics are introduced, the succession could be altered considerably, much to the benefit of postmining generations of Nauruans.
Potential Selective Pressures by Parasitoids on a Plant‐Herbivore Interaction
Authors: Weis Arthur E. , Abrahamson Warren G.
Published: May 2006

The potential role of the third trophic level in the evolution of plant—herbivore relationships was examined in the case of the goldenrod Solidago altissima, and the fly Eurosta solidaginis, which forms a round stem gall. Previous observation had shown that galls attacked by parasites are significantly smaller than those in which the gall maker survives. Two different mechanisms could cause such as pattern: parasite attack could occur before galls reach full size and the attacks could cause early cessation of growth, or attack could occur after galls reach their mature size, but with inherently small galls being more prone to attack. In the first instance, parasite attack would diminish the cost of the gall to the plant, and thus favor plant genotypes that facilitate parasites. In the second instance, parasites would exert selection pressure on the gall marker to induce larger galls. Monitoring of marked plants in the field, and field experiments in which parasites were excluded from gall—bearing plants except during controlled periods, showed that parasite attack does not stop gall growth. The parasitoid wasp Eurytoma gigantea is limited to attacking small galls because of the limited reach of its ovipositor. This created a selection intensity of 0.50, favoring Eurosta that induce larger galls. Evolutionary response to selection could be realized directly through change in the gall marker's stimulus ability, or less directly through phenological changes. Plant activity to the gall marker declined with plant age, so that late—starting galls were more vulnerable to parasite attack.
Barley Straw Decomposition in the Field: A Comparison of Models
Authors: Andren Olof , Paustian Keith
Published: May 2006

Models were applied to results from a field experiment on the decomposition of barley straw, incubated 10—15 cm below the soil surface in a barley field. Litter bags were sampled 14 times during a 2—yr period to follow the dynamics of total mass and chemical components, e.g., water—solubles and total N. Zero— and first—order regression models were fitted to total mass, with and without adjustment for ambient temperature. R2, adjusted for the number of model parameters, was used for comparisons of model fits. The first—order model showed a good fit (R2 = 0.9875) if days with mean soil temperatures @<0°C were excluded. An improved fit was obtained using a temperature correction with Q10 = 1.21 (R2 = 0.9913). A one—compartment simulation model, using temperature and moisture as driving variables, showed a further improved fit (R2 = 0.9952) and a best Q10 = 1.78. Parallel and consecutive first—order models with two components did not improve the overall fit (R2 = 0.9896), but the initial loss of water—solubles coincided well with the predicted initial loss from the labile fraction. To describe the dynamics of selected chemical components, a four—compartment simulation model, including decomposition product formation, was fitted to total mass, water—solubles and total nitrogen. The observed dynamics of these components were well reproduced by the model. Influences of experimental and statistical techniques on interpretations of model results are discussed.
Stem Dynamics of the Shrub Alnus Incana SSP. Rugosa: Transition Matrix Models
Authors: Huenneke Laura Foster , Marks P. L.
Published: May 2006

We constructed transition matrices from observed rates of sprout production and stem growth in two New York state populations of a clonal shrub, Alnus incana ssp. rugosa. The largest real eigenvalue of the transition matrix, l, summarized current population rates of growth. An old—field alder thicket showed slow population decline over all 3 yr of study. The other population, in an undisturbed natural swamp, showed decline in each year but overall increase when data from all 3 yr were combined. Sensitivity matrices were calculated from the stable size distributions and reproductive value vectors for each 3 yr matrix. Sensitivity of population growth rates to specific transitions was illustrated by changing values of the matrix elements and calculating resultant 1 values. Population growth rates were least affected by changes in survivorship of small stems, and most affected by altering sprout production rates and large stem survivorship. Annual variations in demographic rates, and comparisons between actual stem size class distributions and the stable distributions predicted by the matrix models, confirmed the inadequacy of assuming constant transition probabilities. In such a case, transition matrix models are best viewed not as projections of long—term population behavior, but as indicators of current demographic trends.
Disturbance, Pollinator Predictability, and Pollination Success Among Costa Rican Cloud Forest Plants
Authors: Feinsinger Peter , Beach James H. , Linhart Yan B. , Busby William H. , Murray K. Greg
Published: May 2006

Cloud forest at Monteverde, Costa Rica experiences frequent natural disturbance. To determine whether species interactions vary spatially due to physical heterogeneity produced by disturbance, we examined relationships between 22 plant species and 11 nectar—feeding bird species in 14 study plots distributed among three patch types: larger landslide—like gaps (hand—cleared areas along a trail), small gaps (formed by recent treefalls), and understory of closed—canopy forest. Species we describe here flowered in two or three patch types. The aspects of pollination we examined varied little with patch type. Mean frequency of pollinator visits varied with patch type in a few plant species but not in most, and there was no significant trend across species. Pollen loads carried by 314 mist—netted hummingbirds did not vary significantly with patch type, either in total number of grains or number of species represented. Cumulative pollen loads that hummingbirds deposited on stigmas of two species of Acanthaceae (Razisea spicata and Hansteinia blepharorachis) did not vary consistently with patch type, except that Hansteinia flowers in treefall gaps received fewer heterospecific pollen grains than flowers in the other two patch types. Frequency of fruit set varied significantly with patch type in three of the four species examined, but the direction of variation in one of these was opposite to the direction of the other two. The absolute frequency with which flowers were pierced by nectar—robbing hummingbirds did not vary significantly with patch type, although the frequency of piercing relative to legitimate pollinator visits did increase in the large gaps. We attribute the latter result to aggregation of the hummingbird Eupherusa eximia, a chronic nectar robber, at dense clumps of long—flowered plant species that occurred in large gaps. Only one feature we examined suggested that patch type might directly affect the nature of species interactions: in two different analyses, the level of variation in frequency of hummingbird visits to flowers declined from large gaps to small gaps to forest. Results suggest that, unless the disturbance initiating a patch is unusually severe or widespread, interactions between the plants and hummingbirds examined are insensitive to patch type. Such species, existing in naturally dynamic forests throughout their recent evolutionary histories, presumably have become accommodated to frequent small—scale disturbance. Results also suggest that those habitat—related contrasts in plant reproductive traits and plant—pollinator interactions documented in other studies, which compare habitats initiated by anthropogenic disturbances with undisturbed patches, may be artifacts to some extent. Anthropogenically generated disturbance mosaics may promote the spread of species whose reproductive traits evolved under very different circumstances from mosaics generated by natural disturbances.
The Statistical Demography of Whooping Cranes
Authors: Nedelman Jerry , Thompson Jane A. , Taylor Robert J.
Published: May 2006

We fit models for the survivorship of Whooping Cranes to the record of population censuses. We consider two classes of models: those that posit age dependence without time dependence, and those that posit time dependence without age dependence. For the model of Binkley and Miller (1980), which falls in the former category, we develop a correct, stochastic model for the inherent demographic variability. Our re—estimates of the model's parameters support the hypothesis of a temporal and trend in survivorship. We then consider time—dependent models that permit simultaneous inferences about separate temporal patterns of survivorships of juveniles and adults. We find that the evidence is consistent with a 10—yr cycle in survivorship.
Climate, Competition, and the Structure of Temperate Zone Lizard Communities
Authors: Scheibe John S.
Published: May 2006

The roles of climate and competition in relation to the structure of temperate zone lizard communities were investigated. Lizard species richness was positively related to mean January temperature, but negatively related to warm—season precipitation and mean July temperature. Generic groups showed little overlap in morphological factor space but considerable overlap in habitat use. Species that were similar in either morphology or habitat use were dissimilar in the alternative factor space. A canonical correlation analysis revealed a significant relationship between lizard morphology and habitat use. In general, large bulky lizards were associated with extensive vegetative cover while small slenderbodied lizards were found in open desert or grassland conditions. No significant relationship was found between community size and measures of niche overlap or species packing in either morphological or ecological space. A comparison of species packing between the field communities and randomly generated null communities revealed no significant overdispersion of the natural communities in either habitat use or morphology, thus providing no evidence to support the limiting—similarity hypothesis.
Spatial Heterogeneity, Sea Urchin Grazing, and Habitat Structure on Reefs in Temperate Australia
Authors: Andrew N. L.
Published: May 2006

The sea urchin Centrostephanus rodgersii is important in determining biogenic habitat structure on rocky reefs in New South Wales. Individual C. rodgersii, in common with other diadematids, are found in shelters during the day, from which they emerge to forage at night and maintain patches of barrens habitat. The effect of availability of shelter on the foraging behavior of C. rodgersii, and on the abundance of benthic invertebrates and algae, was investigated by a field experiment. Physical heterogeneity in the form of large boulders were translocated between the barrens and Ecklonia forest habitats and arranged so as to either maximize or minimize shelter. The fauna and flora on translocated boulders became progressively similar to that found in the surrounding habitat. Most obvious of these changes were reductions in the density of foliose algae on boulders moved from Ecklonia forest to barrens and reductions in the density of limpets in the reverse translocation. C. rodgersii recruited to all treatments irrespective of where the boulders came from, where they were moved to, and the amount of shelter provided. The availability of shelter was clearly a sufficient condition for the creation of areas of barrens habitat. The reliance on shelter by these sea urchins makes their local distribution and, therefore, that of the barrens habitat, more predictable than in other temperate regions.