bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Behavioral Thermoregulation on Microhabitat Use by Two Sceloporus Lizards
Authors: Adolph Stephen C.
Published: May 2006

I investigated the relationship between microhabitat use and behavioral thermoregulation in the lizards Sceloporus occidentalis and S. graciosus. I studied two populations of each species along a 1300—m elevational gradient in the San Gabriel Mountains of southern California. These species occupy different, but overlapping, elevational ranges, with S. graciosus occurring at higher elevations. Because their ranges differ, the species experience different thermal environments; however, they are nearly identical in several measures of thermal physiology. Body temperatures of active lizards varied little with altitude, although air temperatures decrease substantially over this range. Both species compensated behaviorally for variation in thermal environments by varying basking frequency and microhabitat use. By thermoregulating, lizards maintained body temperatures that favor high levels of locomotor performance and other physiological functions. Microhabitat use varied markedly with elevation. Sceloporus occidentalis was almost completely arboreal at low elevation; lizards of both species were partly arboreal, partly terrestrial at intermediate elevation; and S. graciosus was mainly terrestrial at high elevations. Thus, the species converged in microhabitat use where sympatric. These shifts in microhabitat use paralleled altitudinal changes in (i) the spatial location of thermally suitable microhabitats and (ii) habitat structure. Behavioral thermoregulation, then, appears to be an important determinant of habitat use in these lizards. Results of this study may have important implications for lizard community ecology. Microhabitats that are otherwise appropriate for lizards can be thermally unsuitable depending on the local thermal environment. Hence, the thermal environment and lizard thermal biology constrain patterns of structural habitat use. As a result, physiological considerations could limit the behavioral and evolutionary options for species experiencing interspecific competition. For example, competitors in sympatry may be unable to evolve microhabitat resource partitioning because only a subset of microhabitats are thermally suitable.
Growth Rates and Population Structure of Moraceae Trees in Sarawak, East Malaysia
Authors: Primack Richard B. , Ashton Peter S. , Chai Paul , Lee H. S.
Published: May 2006

To understand the relationship between the dynamics of tropical rain forests and the population processes of individual species, data are needed on the rates at which trees grow, die, and establish. Data on the family Moraceae have been extracted from long—term forestry studies in Sarawak, on the northwest coast of Borneo, an area at the center of species richness of Old World tropical forests. These data can also be combined with forest maps and logging studies to investigate the importance of competition and disturbance in controlling tree growth. Tree populations of Moraceae species had mean annual diameter increments of between 0.4 and 3 mm/yr. Growth rates increased two to six times in the 1st and 2nd yr following (selective) logging, but began to decline somewhat in the 3rd and 4th yr. Growth rate variation among trees in a population was considerable, with most trees showing little or no growth, and a few, high growth rates. Saplings of Artocarpus species increased in diameter at the same mean rate as adult trees. Annual mortality rates were low in primary forest, typically <3%, and indicated stable populations. In logged forest, annual mortality of Artocarpus species was considerably higher, between 5 and 8% for trees and still higher for saplings. Adults and saplings of Ficus, a pioneer species, had much higher annual mortality rates than individuals of Artocarpus. Growth rates of Moraceae trees in primary forest were positively correlated with the growth of the nearest conspecific trees, the mean growth rates of the three nearest neighbors of any species, and the mean distance to the nearest neighbors, but were not correlated with the diameter of the tree itself and the mean diameter of the three nearest neighbors. Analysis of patches of three trees of any species in primary forest revealed that there were no detectable differences among patches in either tree size or growth rate. Tree growth rates of small patches in logged forest were negatively correlated with distance to the nearest forest opening. Even the significant relationships between tree growth rate and immediate neighborhood explained only a relatively small portion of the total variation in growth rate. The remaining variation may be due to variation in plant genotype and local environment.
Effect of Spatial Arrangement of Habitat Patches on Local Population Size
Authors: Fahrig Lenore , Paloheimo Jyri
Published: May 2006

The purpose of this study was to examine the effect of the spatial arrangement of host—plant patches on local abundance of the cabbage butterfly (Piers rapae). By considering the movement behavior of adult females, we developed a detailed simulation model of P. rapae in patchy habitats. The model was then used to predict effects of cabbage patch spatial arrangement on P. rapae egg densities for a specific spatial arrangement of cabbage patches. Field studies confirmed the predictions. The results of this study are discussed in the context of the effects of dispersal behavior on relationships between aptch spatial arrangement and local abundance. The findings are consistent with general simulation results of L. Fahrig and J. E. Paloheimo (personal observation) that suggest large dispersal distances decrease the effect of the spatial arrangement of habitat patches on local population size.
Evolutionary Demography of Orchids: Intensity and Frequency of Pollination and the Cost of Fruiting
Authors: Calvo Ricardo N.
Published: May 2006

Life history theory assumes that there is a trade—off between current reproduction and future growth or reproduction or both; therefore, natural selection is expected to result in the maximization of reproduction within the limits imposed by the trade—off. Accordingly, it has been predicted that fruit and seed production in perennial plants should be resource limited. Many orchid species seem to be pollinator limited, but this hypothesis has been recently challenged by experimental studies that show a cost of increased fruit set in some orchids. In this study, I combined the results of a 2—yr pollination experiment and a 3—yr demographic assessment of a population of the orchid Tolumnia variegata in a matrix model of population dynamics, and by means of simulations I evaluated the effect of pollination intensity and frequency, fruit production, and cost of fruiting on the asymptotic population growth rate. Mean natural fruit set in this population was <1%, whereas intermediate and high pollination intensity resulted in mean fruit set of 35 and 72%, respectively. In any given year, °98% of all flowering individuals fail to set fruit under natural conditions. Despite the dramatic increase in fruit set after hand—pollination, only plants in the high pollination intensity treatment showed a statistically significant reduction in future growth and flowering. The simulation showed that a small seedling production per fruit would be enough to overcome the cost of fruiting; therefore, plants in this population should experience strong selection for increased pollination. This conclusion does not seem to explain the widespread occurrence of low fruit set and high proportion of fruiting failure among nonautogamous orchids. The results of this study suggest an alternative explanation: pollinator limitation could be evolutionarily stable if the correlation between fruit or seed production and seedling recruitment is sufficiently low. If an increase in fruit or seed production does not translate into an increase in fitness, then selection for increased pollination would not occur or would be too weak. The evaluate this alternative, quantitative studies on the transition from seed to seedling in natural orchid populations are required.
Inbreeding Avoidance Increases Dispersal Movements of the Meadow Vole
Authors: Bollinger Eric K. , Harper Steven J. , Barrett Gary W.
Published: May 2006

This study tested whether inbreeding avoidance could influence the frequency and timing of dispersal movements in a small microtine rodent, the meadow vole (Microtus pennsylvanicus). Meadow voles released into experimental grassland plots with siblings were more likely to disperse from these plots than were voles released into similar plots with nonsiblings. Furthermore, voles that dispersed from siblings groups did so sooner than dispersing voles from nonsiblings groups. Voles released with nonsiblings were recaptured within the plots for longer periods than were voles from siblings groups. Males from both groups remained within the plots for shorter times than did females, but the degree of this sex bias was greater for siblings groups. Thus, it appears that inbreeding avoidance can influence dispersal movements of the meadow vole and may be partially responsible for patterns of male—biased dispersal in at least some mammals.
Coexistence of Five Sympatric Piper (Piperaceae) Species in a Tropical Dry Forest
Authors: Fleming Theodore H.
Published: May 2006

Five Costa Rican species of Piper (Piperaceae) co—occur in evergreen forest sites at Santa Rosa National Park, Costa Rica. The species were found to have distinctive spatial distribution patterns with two species (Piper marginatum and P. pseudofuligineum) occurring in early successional sites and the others, P. amalago, P. jacquemontianum, and P. tuberculatum, occurring in less disturbed sites in dry forest, evergreen forest, and riparian forest, respectively. These habitat differences are associated with differences in seed and seedling biology and seasonal changes in the foraging behavior of the chiropteran seed dispersers of these plants. Excluding the uncommon P. tuberculatum, overall pairwise spatial overlap, measured by Pianka's (1974) symmetrical index, averaged 0.61. Relatively low phenological overlap allows the species to share animal visitors. Average pairwise flowering overlap (0.13) was about one—half the value of pairwise fruiting overlap (0.22). Responses to different rainfall cues and/or different inflorescence growth rates produce temporally separated phenological cycles. However, results of computer simulations suggest that observed phenological overlap was neither significantly lower nor significantly higher than expected by chance, for most pairs of species. Insect visitation is necessary for high seed—set, and species differ in their attractiveness to pollinators. Pairwise insect overlap (0.59) was greater than expected by chance, however. The plants also utilize the same six species of frugivorous bats as seed dispersers, and pairwise bat overlap was extremely high (0.96). Because they are important fruit sources for three common bat species, Piper species are keystone mutualists in dry tropical forests.
Seasonal and Diurnal Water Relations Adjustments in Three Evergreen Chaparral Shrubs
Authors: Bowman William D. , Roberts Stephen W.
Published: May 2006

Pressure—volume curves were measured in three co—occurring chaparral shrubs, Arctostaphylos glandulosa, Quercus dumosa, and Ceanothus greggii, during a seasonal drought cycle. The pressure—volume approach was used to quantify diurnal and seasonal changes in plant water relations. Field measurements of plant water potentials and microclimate were also made to relate the pressure—volume results to the field setting. The seasonal trend was toward increasingly negative osmotic potentials with little (Q. dumosa) or no (A. glandulosa and C. greggii) recovery following the end of the drought. Shifts in the turgor loss point occurred both seasonally and diurnally. The largest diurnal shifts occurred during periods of maximum air temperature and minimum soil water potential. Concurrent field measurements of water potential indicate that these shifts were necessary for preventing turgor loss during periods of midday water stress in Q. dumosa and C,. greggii. The shrubs differed in their mode of seasonal osmotic adjustment. Ceanothus greggii accomplished changes in osmotic potential by variation in the osmotic water volume; the other two shrubs appeared to accomplish such changes largely by solute variation while maintaining relatively constant osmotic water volumes.
Size‐dependent Herbivore Attack and the Demography of an Arid Grassland Shrub
Authors: Parker Matthew A.
Published: May 2006

I examined the demographic impact of two specialist insect herbivores on an arid grassland population of the shrub Gutierrezia microcephala in central New Mexico. The grasshopper Hesperotettix viridis may defoliate plants of all sizes, while the root—boring cerambycid beetle Crossidius pulchellus exploits only large, mature plants. During a year of high H. viridis population density (1980), no G. microcephala escaped severe defoliation regardless of size or distance from conspecifics. Over 80% of the plants failed to flower, and mean plant fecundity was over 400 times lower than that of plants experimentally protected from H. viridis attack. Juvenile plants were frequently killed by H. viridis, but only 7% of mature plants of intermediate size (20—30 cm canopy diameter) died following defoliation in 1980. Larger plants had higher mortality rates; this increased risk of death was correlated with a higher incidence of beetle attack in larger plants. Although defoliation virtually eliminated seed production in 1980, seedling abundance in the following spring was not measurably depressed. In addition, G. microcephala seeds germinated abundantly in small areas from which the established vegetation had been experimentally removed. Carry—over of seeds produced in previous years may this provide a source of recruits, despite the occasionally severe impact of grasshoppers on plant fecundity. The local age structure of G. microcephala, obtained by counts of annual growth rings in root crowns, highlights two phenomena that make G. microephala populations vulnerable to local extinction: (1) frequent failures of seedling recruitment (due to drought, grasshopper attack, and competing plants) and (2) the limited longevity of large mature plants, indicated by the rarity of plants older than one decade. Two critical life history stages buffer G. microcephala from these threats to population persistence: the seed pool, which permits opportunistic seedling recruitment during favorable periods; and mature plants of intermediate size, which are resistant to attack by both major herbivores.
Microcosms as Islands: A Test of the Macarthur‐Wilson Equilibrium Theory
Authors: Dickerson Jaime E. , Robinson James V.
Published: May 2006

A test of the MacArthur—Wilson equilibrium model of island biogeography was conducted using aquatic microcosms as island analogs. Fifty 400—mL beakers containing 300 mL of sterilized soil—water medium and 50 2000—mL beakers containing 1800 mL of medium were inoculated with replicated subsets of species from a species pool consisting of green, blue—green, and golden algae, ciliates, a rotifer, a dinoflagellate, and euglenoids. These species were added at two different average rates over a 28—wk period, resulting in four replicated sets of 25 insular communities. Community reorganization (turnover) was shown to occur, as well as relatively constancy in species richness for each beaker category, indicative of equilibrium. Contrary to the MacArthur—Wilson prediction, small microcosms had significantly higher species richness values than large microcosms. Microcosms subjected to the higher of the two invasion rates had significantly higher species richness values than those of the lower rate categories, primarily due to the influence of transient species. Early divergence into two broad community types is documented, suggestive of at least two stable community states that transcend microcosm categories.
Recruitment of Coral Reef Fishes: Effects of Distribution of Predators and Shelter
Authors: Shulman Myra J.
Published: May 2006

Factors affecting recruitment and early survivorship of juvenile coral reef fishes were studied on St. Croix, United States Virgin Islands. The faunal assemblage studied included diurnally active fishes found in the rubble/sand habitat. The most abundant members were: beaugregory (Stegastes leucostictus), foureye butterfish (Chaetodon capistratus), mahongany snapper (Lutjanus mahogoni), surgeonfishes (Acanthurus bahianus and A. chirurgus) and French grunt (Haemulon flavolineatum). During the period 1978—1981, set of experimental reefs constructed from Strombus gigas shells were built in various locations relative to a major reef. Recruitment of juveniles of almost all species in the rubble/sand fish assemblage occurred more heavily on reefs that were built 20—40 m away from the main reef (into the lagoon) than on those built at the edge of the backreef. A series of experiments revealed that this is probably due to two factors: differences in available shelter and differences in encounter rates with predators. Seagrass and algae, which provide shelter to very small juvenile fishes, are absent in a "halo" zone close to the reef due to the feeding activities of reef—associated grazers (fishes and urchins). Experiments with artificially produced halos and artificial seagrass and algae showed that part of the explanation for the observed spatial pattern of fish recruitment is the spatial pattern of the shelter provided by seagrass and algae. Experiments in which potential prey fish were tethered demonstrated that the risk of predation for small juvenile fishes was considerably higher close to the reef than it was 20 m away. The results of these experiments suggest that patterns of settlement and juvenile survivorship of coral reef fishes are affected by complex interactions with other reef organisms (in this case, he activities of reef—associated grazers that modify available shelter) and by the frequency of encounters with predators. If they survive, all of the juveniles, regardless of where they initially settle, eventually migrate to a nearby reef. The species studies here differed in the degree to which juveniles use the sea—grass/algal habitat as a refuge from predation; these differences suggest that spatial patterns of recruitment, interacting with predation, may influence both population abundances and species composition of older juveniles on the reef.
Fungal Mediation of a Plant‐Herbivore Interaction in an Early Successional Plant Community
Authors: Bowers Michael A. , Sacchi Christopher F.
Published: May 2006

We used a series of fenced exclosures to examine whether herbivory by mammals affected the structure and dynamics of an old—field plant community in Virginia. Early in the 3rd yr of the study purple clover, Trifolium pratense, a dominant member of the plant community, occurred at higher densities where herbivores were excluded relative to control plots. Following a 1—mo time lag, Trifolium became infected by the rust—forming fungal pathogen Uromyces trifolii; the incidence of infection was higher in exclosures relative to control plots where herbivores were present. Early—to—late season changes in the abundance of Trifolium were related to the degree of fungal infection and not herbivore presence/absence. Data from the following year (when the fungus and Trifolium were rare) showed clover abundance to be higher in control plots than in exclosures. These results suggest that the negative influence of the fungus not only persisted through time, but more strongly affected host plant abundance in a 2—mo period than did herbivory that occurred in both years. While the direct effect of herbivory on food plants is negative, by keeping plant abundance below that at which fungal infections become epidemic, the net effect of herbivores on some forage plants may be positive. The existence of strong indirect interactions is further evidence that the emphasis in community ecology (and in plant succession) should be on interactive networks rather than on species pairs.
Weasel Population Response, Home Range, and Predation on Rodents in a Deciduous Forest in Poland
Authors: Jedrzejewski Wlodzimierz , Jedrzejewska Bogumila , Szymura Lucyna
Published: May 2006

Numerical responses of the weasel Mustela nivalis to the changes in population density of forest rodents (bank vole Cleothrionomys glareolus and yellow—necked mouse Apodemus flavicollis) and predation by weasels studied in the pristine deciduous forests of Bialowieza National Park, eastern Poland, in 1985 through 1992. The rodents experienced 5 yr of noncyclic (seasonal) fluctuations (autumn density 23—74 rodents/ha) and 2 yr of outbreak and crash (triggered by synchronous heavy crop of oak, hornbeam, and maple seeds). Autumn numbers of rodents exceeded 300 individuals/ha during the outbreak and dropped to 8 individuals/ha in the following autumn. Weasels were censused by livetrapping in summer and by snowtracking on an 11.2—km2 grid of transects in winter. Radiotracking of 12 weasels in 1990 and 1991 yielded estimates of home ranges and daily movement distances, which were combined with snowtracking and livetrapping data to estimate densities during 7yr. Estimated winter density of weasels varied from 5.2 to 27.3 individuals/10km2 in December and declined to 0—19.1 individuals/10 km2 by early spring (March). Midsummer (July/August) indices of weasel numbers were extremely variable and corresponded to 41.9—47.6 individuals/10 km2 in years with moderate density of rodents, 101.7 individuals/10 km2 during the rodent outbreak and 19.1 individuals/10 km2 during the crash. Increase of weasel numbers from spring to midsummer was positively related to the spring numbers of rodents. Autumn and winter decline of weasel numbers was not related to rodent density changes. During the outbreak and crash of the rodent population, the numbers of weasels and rodents (both sampled at 2—3 mo intervals) were positively correlated (P < 0.0005) with no time lag. Home ranges of male weasels radiotracked during the rodent outbreak were 11—37 ha (minimum convex polygon), compared to 117—216 ha during the crash year. The predator/prey ratio varied from 0 to 2.5 weasels/1000 rodents. The ratio was highest at low densities of rodents. With increasing numbers of rodents, the ratio declined, since rodent population growth was overwhelmingly faster than weasel population growth. In the 7 autumn—winter seasons (1 October—15 April), weasels removed, on average, 1.6 to 9.5 rodents from each hectare, i.e., from 2 to 28% of autumn numbers of rodents. Winter predation by weasels was heaviest at rodent density of °20 individuals/ha. At lower densities of rodents, the number of weasels was restricted by food shortage and the role of their predation rapidly declined. At high rodent densities, the rodent numbers by far exceeded the predatory capacity of weasels and predation percentage declined again. Weasel predation in relation to rodent density has the same pattern in geographic zones ranging from Turkmen deserts to European farmlands and forests.
Fate of Seeds Adapted for Dispersal by Ants in Australian Sclerophyll Vegetation
Authors: Hughes Lesley , Westoby Mark
Published: May 2006

Influences of ant behavior on short— and long—term fate of elaiosome—bearing seeds were investigated in fire—prone sclerophyll vegetation neary Sydney, New South Wales. The short—term fate of seeds was assessed by measuring dispersal distances, seed predation within ant nests, and seed burial. Most seeds were taken directly to ant nests. The mean dispersal distance was 1.1 m (range 0.06—11 m). Seed predation by three ant species was measured by feeding known quantities of seeds and inedible seed mimics, made from plastic beads, into nests. Nests were excavated 2, 7, and 30 d later to recover seeds and beads. The recovery rate of beads estimated the disappearance rate of seeds from nests due to factors other than predation. Pheidole sp. 1 appeared to eat most seeds soon after collection but also stored some seeds in small caches within the nest. Both Rhytidoponera "metallica" and Aphaenogaster longiceps removed most seeds for the nest intact (the elaiosome having been consumed) and discarded them on the surface, but left some within nests at depths <12 cm. Seeds discarded on the soil surface may undergo secondary dispersal by other ants. A transition matrix analysis was used to assess the importance of this secondary dispersal route and to estimate the probabilities that seeds initially taken by a particular ant species would be either eaten or finally buried within a nest. The analysis indicated firstly that a significant proportion of seeds initially removed by A. longiceps and R. "metallica" will eventually be eaten by Pheidole spp. Secondly, some seeds will be discarded in the nests of species other than the original seed remover. The analysis also indicated that seeds initially taken by A. longiceps and R. "metallica" would be more likely to survive than those taken by Pheidole sp. 1. As many Australian ant—dispersed seeds are stimulated to germinate by fire, long—term seed fate was investigated by monitoring seedling emergence after fire from ant nests that had been fed a known quantity of seeds. Overall emergence was °1% of seeds fed into nests. The greatest emergence was from nests of A. longiceps. This result is qualitatively consistent with those of the short—term experiments. However, the low overall emergence rate meant the power of this experiment to detect statistical differences between ant species was limited. The spatial pattern of emerging seedlings differed between nests of the different ant species. Seedlings from the nests of Pheidole sp. 1 were considerably more clumped than those from nests of the other three species. The seed fate experiments collectively indicated that seed—removing ants have different effects on seed fate, with A. longiceps and R. "metallica" being more beneficial than Pheidole.
Dispersal and Disease Gradients of Anther‐Smut Infection of Silene Alba at Different Life Stages
Authors: Roche Bernadette M. , Alexander Helen Miller , Maltby Arlan D.
Published: May 2006

Given the increased recognition of the importance of spatial aggregation of infected individuals on disease spread, we used a field experiment to examine spore dispersal and disease transmission at increasing distances from an inoculum source in a well—studied system, the herbaceous plant Silene alba, infected by the anther—smut fungus Ustilago violacea. Two different life stages (vegetative and floral) were examined. We measured spore deposition on flowers and, as an analog of dispersal to vegetative plants, in small vials on the ground. Spore and disease gradients (number of spores or proportion of plants infected as a function of distance) were best fit with the classic power, Y = aD—b. The slope parameter, b, were similar for spore dispersal gradients of vegetative (b = —2.38) and flowering plants (b = —1.91). However, at every distance measured, the proportion of flowers with spores was higher than the proportion of ground vials with spores, indicating overall higher relative spore dispersal to flowering plants. We also determined that disease gradients for flowering plants were more shallow (b = —0.07) than spore dispersal gradients, and vegetation infection was more spatially restricted than floral infection (no infection beyond 3.2 m for vegetative plants while floral infection was detected up to 11.2 m). The relationship between spore dispersal and disease incidence was linear for vegetative plants and curvilinear for flowering plants, with limiting returns on disease after a low threshold number of spores deposited. Overall, our study suggested that the limited dispersal of spores is likely to be important in the aggregation of diseased plants in nature; such aggregation of inoculum in turn can increase or decrease disease spread depending on how much inoculum is needed to cause infection.
A Physiology‐Based Gap Model of Forest Dynamics
Authors: Friend A. D. , Schugart H. H. , Running S. W.
Published: May 2006

A computer model of forest growth and ecosystem processes is presented. The model, HYBRID, is derived from a forest gap model, an ecosystem process model, and a photosynthesis model. In HYBRID individual trees fix and respire carbon, and lose water daily; carbon partioning occurs at the end of each year. HYBRID obviates many of the linitations of both gap models and ecosystem process models. The growth equations of gap models are replaced with functionally realistic equations and processes for carbon fixation and partitioning, resulting in a dynamic model in which competition and physiology play important roles. The model is used to predict ecosystem processes and dynamics in oak forests in Knoxville, Tennessee (USA), and pine forests in Missoula, Montana (USA) between the years 1910 and 1986. The simulated growth of individual trees and the overall ecosystems—level processes are very similiar to observations. A sensitivity analysis performed for these sites showed that predictions of net primary productivity by HBRID are most sensitive to the ratio of CO2 partial pressure between inside the leaf and the air, relative humidity, ambient CO2 partial pressure, precipitation, air temperature, tree allometry, respiration parametes, site soil water capacity, and a carbon storage parameter.
Empirical Evidence of the role of Heterogeneity in Ratio‐dependent Consumption
Authors: Arditi Roger , Saiah Henni
Published: May 2006

An increased probability of death is thought to be an inherent risk of dispersal. To examine this hypothesis, were monitored 381 radiomarked Ruffed Grouse (Bonasa umbellus) over 6 yr to determine if their vulnerability to mortality increased during dispersal. Estimates of mortality were calculated for the two distinct phases of dispersal: transience, a period of extensive movement from one area to another, and colonization, the period when an animal attempts to become established in a new area. Among juveniles (nonresidents), approximately equal proportions of both sexes exhibited transience, and for similar lengths of time. The difference between juvenile male and female mortality estimates was not significant during either transience or colonization. From autumn to spring (natal dispersal), juvenile transient dispersers did not experience greater mortality than colonization dispersers. Among adults, transience was more common among females than males, yet no mortality was recorded among either sex of adult transient dispersers. Residents (adults) survived at a higher rate than juveniles in either transient or colonization dispersal. However, the cost (i.e., increased mortality) of transience was greater for juveniles than adults, suggesting comparisons between different phases of dispersal be made within similar age classes. It was concluded that Ruffed Grouse, both adults and juveniles, were not more vulnerable to mortality during transient dispersal than during colonization dispersal.
Higher Reproductive Success among Kin Groups of Bank Voles (Clethrionomys Glareolus)
Authors: Mappes Tapio , Ylonen Hannu , Viitala Jussi
Published: May 2006

According to the kin selection theory the degree of genetic relatedness affects the nature of intraspecific competition and it might promote cooperative and/or altruistic behavior between individuals. We examined kinship effects on reproductive success of territorial females and survival of juveniles in the bank vole Clethrionomys glareolus. Four experimental populations were founded in large enclosures (0.5 ha): two consistent of five related (Related, R) and two of five mutually unrelated females (Unrelated, UR). Each population had five males of heterogeneous origin. Our earlier results showed that populations of the R grew twice as fast as the UR. Here we show that recruitment and offspring survival is connected to spacing behavior of mothers. Unrelated females who had their home range close to each other produced significantly fewer recruits that the related ones. There home ranges overlapped significantly less and ranges were smaller if they were situated close to each other. Furthermore, the survival of juveniles declined with dispersal distance from the natal territory in populations of the UR. Trappabilities of juveniles were also lower among the young whose home range were close to unrelated females, indicating avoidance of mature females. Our results indicate that competition for space is more intense among related neighbors, decreasing their reproductive success. Infanticide towards unrelated nestlings and/or juveniles is one possible mechanism decreasing survival and causing a lower recruitment of young. On the contrary, sharing of space among related neighbors did not seem to cause notable costs on their reproduction. Mature females allowed related young females to use their territory, but still, the young did not acquire an area for their own reproduction, probably due to a mother—daughter conflict. The basic social structure of Clethrionomys populations, i.e., exclusive female territoriality, remain the same regardless of a high degree of relatedness.
Fossil and Genetic History of a Pinyon Pine (Pinus Edulis) Isolate
Authors: Bentancourt Julio L. , Schuster William S. , Mitton Jeffry B. , Anderson R. Scott
Published: May 2006

The most isolated northern stand of Colorado pinyon pine (Pinus edulis) at Owl Canyon, Colorado, USA has a broad and flat size class distribution common to population expansions, with the largest and oldest trees near the center of the grove. Analyses of fossil packrat (Neotoma sp.) middens within the grove indicate that the stand originated by long—distance dispersal rather than by vicariance, a distinction seldom possible because of the unknown or incomplete histories of such isolated populations. Our 5000—yr pollen and macrofossil record suggests that pinyon pine colonized the site sometime between 1290 and 420 yr BP, the latter age corresponding to the oldest tree in the stand. Electrophoretic data from living trees show that this colonization was not attended by typical founder effects predicted by theory or observed for other known founder events. Despite its isolation, recent founding, and probable long—distance origin, the Owl Canyon stand has not suffered significant losses in genetic variation relative to likely source populations. Large initial population size, multiple founding events, rapid population growth, or selection favoring heterozygous genotypes could all explain the high heterozygosity and only slightly reduced polymorphism and number of alleles per locus found in the Owl Canyon stand. These results demonstrate the genetic complexity of founder events and the utility of blending complementary approaches such as paleoecology and genetics to better understand the population biology of peripheral isolates.
Are Food Webs Randomly Connected?
Authors: Kenny David , Loehle Craig
Published: May 2006

We present a simple random model for food web connectance. We model observed webs as random samples drawn from the universe of all possible randomly connected sets of n objects, with no biological interactions assumed. We then drop out links based on observed link—magnitude data and sampling effects. The resulting connectance curves nicely bracket real data, suggesting (1) that food webs may in fact be randomly connected, and (2) the mere fact that previously proposed models can generate the observed connectance values does not guarantee the correctness of the models. This study also suggests that studies of food web topological properties may bear reexamination.
The Influence of Larval Supply and Settlement on the Population Structure of Barnacles
Authors: Minchinton Todd E. , Scheibling Robert E.
Published: May 2006

The abundance and distribution of settlers, recruits, and adults of the barnacle Semibalanus balanoides were monitored in the high, mid, and low intertidal zones at two adjacent, but physically and biologically different sites (A and B) on a rocky intertidal shore in Nova Scotia following a rare occurrence of ice scouring. Availability of planktonic cyprid larvae also was measured at site A. There was a strong concordance between cyprid availability and settler density over the main settlement period among intertidal heights, where each was inversely related to intertidal height. Differences in cyprid availability with intertidal height were related to immersion time as the larvae, in general, were uniformly distributed at the water—substratum interface. Settlement rate was strongly correlated with cyprid availability in the low intertidal zone at site A, where most settlement occurred. In all zones at both sites, recruit density at the end of the main settlement period was a positive function of settler density over this period: on average, 79% of the variation in recruit density was explained by settler density over the main settlement period. Adult density and total settler density also tended to be strongly related: 86% (mid zone at site A) and 73% (high zone at site B) of the variation in adult density was explained by total settler density, except where postrecruitment mortality (i.e., predation) was high (e.g., only 1% of the variation in adult density was explained by total settler density in the low zone at site A). Local hydrodynamics, which influences supply and distribution of planktonic larvae, may dictate the distribution of settlers and, ultimately, adults on this shore.
Diet Specialization Limits Herbivorous Sea Slug's Capacity to Switch Among Food Species
Authors: Trowbridge Cynthia D.
Published: May 2006

Sympatric, conspecific animals may use resources in different ways: a population of foragers with a generalist diet may be composed of polyphagous individuals or of different types of oligophagous individuals. The sea slug Placida dendritica (Opisthobranchia: Ascoglossa) exhibited the latter pattern. Individuals slugs from different green algal host species exhibited different rank preferences of and performances on host species. Feeding preferences did not change through time and were independent of Placida size. In addition, the slug's highly rigid feeding specificity was not modified through hunger level, algal condition, or social interactions with experienced conspecifics. Thus, Placida frequently died when maintained on "unfamiliar" host species that sympatric conspecifics consumed. The extreme trophic specialization of Placida suggests that the costs of switching host species may be extremely high in short—lived foragers.
Diffusion Resistance and Xylem Potential in Stressed and Unstressed Northern Hardwood Trees
Authors: Federer C. A. , Gee G. W.
Published: May 2006

In a northern hardwood forest in central New Hampshire, daytime diffusion resistances of abaxial leaf surfaces were independent on light level above 250 @mE/(m2°s), increased as vapor pressure deficit increased, and decreased as temperature increased. High vapor pressure deficit at midday caused slight stomatal closure, which appeared to be independent of leaf H_2O potential. Low plant H2O potential may have produced additional closure at high atmospheric demand even though soil—water potential was > —0.2 bar. At an atmospheric demand of 250 W/m2 xylem potential averaged —16 bar for Betula alleghaniensis, —21 bar for Acer saccharum, and —23 bar for Fagus gradifolia, and decreased only slightly as demand increased further. Daytime diffusion resistance averaged 2.5 s/cm for B. alleghaniensis, 3.1 s/cm for A. Saccharum, and 3.3 s/cm for F. grandifolia when light was adequate. The resistance difference implies the possibility of higher transpiration rates in B. alleghaniensis. Several trees were artificially stressed by trenching around them and covering the soil block with polyethylene. After 2—3 wk with rain excluded, soil—water potential ranged from —0.4 to —0.8 bar, and daytime diffusion resistance averaged 5 s/cm, indicating significant stomatal closure caused by H_2O stress. However daytime xylem potentials on stressed trees were the same as or higher than those on unstressed trees. Stomatal control effectively prevented excessive H_2O loss and prevented xylem potential from declining below normal operating levels.
Environmental Control of Primary Productivity in Alaskan Tundra Ponds
Authors: Stanley Donald W. , Daley Ralph J.
Published: May 2006

The photosynthetic response of tundra pond algae to various combinations of temperature, light intensity, and phosphate concentration was measured at weekly intervals during the 1973 summer. In these small (50 m diam by 20 cm deep) ponds near Barrow, Alaska the epipelic algae had a higher temperature optimum (> 20 degrees C) for photosynthesis than did the phytoplankton (14 degrees C) but the epipelic Q_(10) (2.5—12.5 degrees C) for photosynthesis was only 2.2, compared to a value of 3.0 for the planktonic algae. Thus the epipelic algae seemed to be adapted to the sediment environment where temperatures were usually higher than temperatures in the water. The plankton algae, in contrast, appeared to consist of species which photosynthesized more efficiently at the lower temperatures of the pond water. The photosynthetic half—saturation light intensity, I_(0.5), was temperature dependent, increasing as much as threefold in the epipelic experiments (from 0.04 to 0.12 ly° min—1) over a 10 degree temperature range. No diurnal change in I_(0.5) was observed but it declined steadily for both algal groups throughout the summer in response to declining illumination. This decrease in I_(0.5) probably resulted from an increase in the chlorophyll—to—carbon ratio of the algae. Light inhibition was common at low temperatures in the planktonic experiments but never occurred in the epipelic experiments. Short—term phosphate enrichment experiments resulted in no detectable response in either plankton or epipelic algal photosynthesis. However, after whole pond fertilizations large increases in algal biomass and productivity occurred within several days. Thus, the ponds were phosphate—limited but there was a time lag in the response to the nutrient addition.
Primary Production in a Louisiana Golf Coast Spartina Alterniflora Marsh
Authors: Kirby Conrad J. , Gosselink James G.
Published: May 2006

Live and dead aboveground biomass of Spartina alterniflora Loisel in a Louisiana salt marsh was determined monthly over an annual cycle. Litterbags were used to determine loss rates of particulate vegetation from the marsh surface. Net aboveground primary production estimates ranged from 750 to 2,600 g m(—2) yr(—1), depending on how data were handled. Analysis of these results suggested that true net production was probably much closer to the highest estimate, than to the lowest.
The Contribution of Typha Components to Floating Mat Buoyancy
Authors: Hogg Edward H. , Wein Ross W.
Published: May 2006

The seasonal contribution of living Typha components to the buoyancy of floating mats was investigated in a diked, freshwater impoundment near the head of the Bay of Fundy in New Brunswick, Canada. The objectives were (1) to examine the potential influence of a dominant, mat—building species on hydrologic conditions at the mat surface, and (2) to predict whether a complete killing of the dominant species could cause mats to sink. The Typha component contributing most to mat buoyancy was the rhizomes, which added a net buoyancy pressure of °20 Pa throughout the growing season. The seasonal maximum buoyancy contribution of 28 Pa for all living Typha components combined was reached in spring, followed by a decline to 11 Pa in late summer as the aboveground shoots developed. This positive and seasonally variable contribution of Typha to mat buoyancy is expected to be most important during the early stages of mat development, when mats are thin and composed largely of living, belowground organs. However, on older and thicker mats the living Typha is less important because of the large volumes of gas bubbles from anaerobic decomposition that are trapped in the dead organic material. For the 50 cm thick floating mats under study, it is concluded that trapped gas is the main cause of buoyancy and would lead to the continued flotation of mats even if the living Typha were removed. Implications of the results are discussed in relation to the resiliency of floating mat systems.
Saturniid and Sphingid Caterpillars: Two Ways to Eat Leaves
Authors: Bernays E. A. , Janzen D. H.
Published: May 2006

We demonstrated allometric differences in relative head mass in different instars of 12 species of Saturniidae and 14 species of Sphingidae. The differences were related to the different ways in which individuals from the two families ate their respective host plants and to the different properties of the hosts that tended to be favored by each lepidopteran family. The saturniids tended to have various simple cutting methods, while the sphingids tore and crushed the food, so that in the former, ingested food was in the form of relatively large uniformly sized pieces, and in the latter it was apparently well masticated. Saturniid mandibles were short and simple, while sphingid mandibles were long, toothed, and ridged in a variety of complex ways. The food of saturniids tended to consist of old, tough, tannin—rich leaves, while that of sphingids was softer, younger, and contained small toxic molecules. The generalists within each group tended to be similar to one another, while the specialists (which occurred more frequently among the sphingids) had very characteristic mandibles, each of unique design. One sphingid species feeding on a vine with characteristically very tough leaves had the "saturniid" design of mandibles. The features typically of the two groups of caterpillar are discussed in relation to feeding strategy, digestion, avoidance of plant "defenses," and rapidity of ingestion.
Stability of Rocky Intertidal Surfgrass Beds: Persistence, Preempton, and Recovery
Authors: Turner Teresa
Published: May 2006

Experiments were used to study the mechanisms underlying the persistence of beds of the surfgrass Phyllospadix scouleri, a prominent feature on horizontal benches in rocky intertidal areas ranging from British Columbia to Baja California. The stability of P. scouleri beds was investigated by: (1) quantifying structure and persistence, (2) experimentally removing P. scouleri, and (3) measuring rates of recovery from disturbance. At two Oregon study sites P. scouleri not only occupied more space than any other species but also persisted through all seasons for 3 yr. Differences between the two sites seem related to their disturbance patterns; although new free space was rarely created at either site (0.13 and 0.04% of the area per year), P. scouleri occupies much more space at the site where it is less often disrupted. Experimental removals of P. scouleri (0.25—m2 plots) resulted in significant increases in algal cover and in upright—plant diversity, suggesting that it preempts space from other species. These invading algal species dominated the experimental plots for the remainder of the study. During the 3—yr experiment only nine surfgrass seedlings recruited into 28 plots and occupied <1% cover. Mapped seedlings in a 28—m2 area experienced 93% mortality in 7 mo. Rhizomes of surrounding P. scouleri plants grew into experimental plots at a maximum increase in rhizome length of 6 cm/yr. The slow recovery makes even the rare disturbances that occur in these communities important. Therefore, P. scouleri beds have high persistence stability, despite their slow recovery. They owe this persistence mainly to their high preemptive ability. These characteristics appear common to many species with escapes from herbivores.