bluuebunny/crossref_metadata_2025 huggingface dataset:
Behavior and Phenology of a Specialist Bee (Dieunomia) and Sunflower (Helianthus) Pollen Availability
Authors: Minckley Robert L. , Wcislo William T. , Yanega Douglas , Buchmann Stephen L.
Published: May 2006

The phenological relationships between nesting behavior of a specialist, solitary bee, Dieunomia triangulifera, and the flowering of its primary pollen source, Helianthus annuus, were studied for 3 yr at a site in northeastern Kansas, which contained between 50 000 and >150 000 nests. Activity patterns of D. triangulifera are closely synchronized with pollen availability on nearby sunflower plants in three ways: (1) each year, D. triangulifera became active within days of the beginning of the local sunflower bloom, and the emergence schedule of the entire population at the nest site was timed such that all females had constructed nests and were collecting pollen at peak bloom; (2) over a season the greatest numbers of provisioning females were active at peak bloom, when pollen was most abundant; and (3) over the day, females made more trips, each of which took less time when pollen was most abundant on nearby flowers than when it was scarce. Between seasons, female reproductive success varied positively with the availability of H. annuus pollen. When pollen was abundant, and the population at the nest site was low, °3 times more cells were provisioned than the following year when the bee population was high and pollen abundance declined. Furthermore, 20 pollen—collecting bee species (10 specialists and 10 generalists), besides D. triangulifera, used an estimated 68% of the available sunflower pollen at this site. These data suggest that resource limitation is important in shaping patterns of provisioning behavior in D. triangulifera. Other behaviors presumably related to reproductive success were variable and suggest resources were not limiting: (1) all females did not forage on each day, even at peak bloom; (2) variance in both trip durations and the numbers of trips made per day was large; and (3) females produced far fewer eggs in their lifetime than apparently possible. We suggest that the apparently conflicting evidence for resource limitation may be explained by a physiological limit on the rate of egg production; in such a case, the effects of resource limitation, while clearly important, might not be the primary factor limiting reproductive output. Female D. triangulifera benefit by being synchronized with their resource. Daily and seasonal synchrony enable females to collect a greater amount of pollen during shorter foraging trips. The translates into higher mean reproductive success and, at the population level, allows more females to be supported by the pollen produced from nearby plants. In short, those females that are synchronized with the sunflower bloom effectively increase their own resource availability. This phenomenon may be general, especially in short—lived organisms, i.e ., the evolution of specialization may be associated with fitness benefits based on synchrony with a preferred food source.
Soil and Stem Water Storage Determine Phenology and Distribution of Tropical Dry Forest Trees
Authors: Borchert Rolf
Published: May 2006

Many trees of tropical dry forests flower or form new shoots soon after leaf shedding during the dry season, i.e., during a period when trees are likely to be severely water stressed. To resolve this apparent paradox, phenology and seasonal changes in tree water status was monitored during two consecutive dry seasons in >150 trees of 37 species growing at different sites in the tropical dry lowland forest of Guanascaste, Costa Rica. Tree development during the dry season varied considerably between species and between sites of different moisture availability. Leaf shedding, flowering, and shoot growth (flushing) were strongly correlated with seasonal changes in tree water status, measured by conventional and newly developed techniques. Tree water status varied with the availability of subsoil water and a variety of biotic factors such as structure and life—span of leaves, time of leaf shedding, wood density and capacity for stem water storage, and depth and density of root systems. Observed tree species differed widely in wood density (from 0.19 to 1.1. g/cm3) and stem water storage capacity (400—20% of dry mass), which was highly correlated with the degree of desiccation during drought. Only hardwood trees at dry upland sites, lacking stem water storage and access to subsoil water, desiccated strongly (stem water potential <—4 MPa) and remained inactive throughout the dry season. In all other trees elimination of transpirational water loss during leaf shedding in conjunction with utilization of residual water enabled rehydration of stem tissues and subsequent flowering or flushing during the dry season. Rate and degree of rehydration varied strongly with the availability of water stored in tree trunks or in the subsoil. Stored water buffers the impact of seasonal drought and enables flowering and flushing during the dry season. Climatic data thus not sufficient to explain tree phenology in seasonally dry tropical forests. Phenology, seasonal changes in water status, and water storage capacity of tree species are highly correlated. Tree species cluster into a number of distinct functional types ranging from deciduous hardwood trees and water—storing lightwood trees in dry upland forests to evergreen light— and softwood trees confined to moist lowland sites. Seasonal variation in tree water status thus appears to be the principal determinant of both phenology and distribution of tree species in tropical dry forests.
Long‐Term Trends in Forest Net Primary Productivity: Cascade Mountains, Washington
Authors: Graumlich Lisa J. , Brubaker Linda B. , Grier Charles C.
Published: May 2006

Estimates of annual net primary productivity since 1880 for four high—elevation forest stands in western Washington indicated that productivity has increased 60% during the 20th century. Because these stands were separated by up to 200 km and differed in species composition, elevation, and time since establishment, the observed trends in productivity imply a response to regionwide changes in environmental factors rather than to site—specific stand dynamics. Annual production is significantly correlated with long—term variation in summer temperature and short—term variation in annual precipitation since 1983, the beginning of continuous local meteorological records. Production is uncorrelated with atmospheric CO2 concentrations, suggesting that direct CO2 fertilization is currently unimportant in these forests.
The Importance of Recruitment to the Dynamics of a Coral Reef Fish Population
Authors: Jones Geoffrey P.
Published: May 2006

An experiment on a coral reef fish is described that assesses the effects of recruitment success on adult abundance over a 3—yr period. The damselfish Pomacentrus amboinensis was examined on natural patch reefs of °8 m2 in the lagoon of One Tree Reef. Recruitment levels were adjusted to 0, 0.5, 1, and 2 recruits m—2°yr—1 by transplanting juveniles among reefs at the end of four successive recruitment seasons (with four replicates per treatment). Natural recruitment success was monitored on 16 undisturbed reefs, and adult numbers were monitored at irregular intervals on both experimental and undisturbed reefs. The adult population density at the end of the experiment increased significantly with recruitment within the 0—1 recruit/m2 range. However, doubling recruitment from 1 to 2 recruits/m2 did not lead to any further increase in adult density. The recruitment treatments did not affect adult density until a 2—yr period had elapsed (corresponding to average maturation time). At this time, treatments receiving 1 and 2 recruits/m2 showed a dramatic increase in adult numbers, whereas in the low—recruitment treatments, adult densities declined. The experiment indicated that a recruitment success of between 0.5 and 1 recruit/m2 was necessary to maintain adult numbers at pre—experimental levels. Natural recruitment success was highly variable among years, but adult densities remained relatively constant over time at °0.8 adult/m2. Differences in the final adult densities among reefs were correlated with average recruitment levels, but above 0.8—1.0 recruit/m2, adult densities did not increase with increasing recruitment success. The results from experimental and undisturbed reefs suggest that natural variation in recruitment success affects the importance of post—recruitment processes. In good recruitment years, adult densities on a substantial number of reefs may be limited by density—dependent processes, which may affect the majority of individuals in a region. Density—dependent juvenile growth may buffer adult populations on these reefs against the effects of poor recruitment years, since input may come from a number of immature age classes. Where recruitment success is always below a certain level, the dynamics of adult populations will reflect variation in recruitment success.
Optimal Foraging and Habitat Shift in Perch (Perca Fluviatilis) in a Resource Gradient
Authors: Persson Lennart , Greenberg Larry A.
Published: May 2006

To better understand how and why foraging shifts between habitats and among prey occur, and to evaluate the ability of an optimal foraging model to predict diet breadth quantitatively, we studied the food and habitat use of perch (Perca fluviatilis) in an experimentally induced resource gradient. The purpose of the study was also to see whether prey—type—dependent search rates were important for observed resource utilizations. The resource level in one (pelagic) of two (pelagic and benthic) habitats was selectively reduced in a field experiment by varying the densities of roach (Rutilus rutilus), and interspecific competitor of perch (Perca fluviatilis) that feeds preferentially on pelagic resources. We tested whether a simple optimal foraging model could predict (1) the diet breadth of perch and (2) when perch should shift from feeding in the pelagic habitat to the benthic habitat. The experiment was carried out in a pond divided into 10 enclosures. Perch density was held constant between enclosures, whereas the density of the planktivorous competitor was varied among enclosures. The smallest size classes of pelagic prey used by perch correspondence with what was predicted by the basic prey model. However, the mean prey size in the diet of perch was larger than that predicted by the model. For benthic prey, diet breadth was poorly predicted, reflecting the problem of extrapolating laboratory—estimated encounter rates and handling times to more complex habitats in the field. During the first half of the experiment, but not during the second half, there was a positive correlation between the growth rate of perch and the predicted net return rate from feeding on pelagic prey, based on the foraging model. Conversely, no significant relationship between perch growth performance and predicted net energy intake from the benthic habitat was present during the first half of the experiment, while a positive relationship was present during the second half. There was a time lag between predicted and observed shifts in habitat use from pelagic to benthic feeding. In addition, the habitat shift was never complete since perch continued to feed on some pelagic prey after having shifted to feeding mainly on benthic prey. Different optimal search rates for prey in different habitats may have given rise to time lags in habitat shifts as well as to partial habitat use. Habitat—dependent search rates may thus form a complementary explanation to learning and sampling behavior, for observed time lags and partial habitat use. Flexible predator search rates reinforce the importance of considering the whole behavioral repertoire of predator and prey, not only the predator's choice once prey has been encountered.
The Scaling of Sound Output and Territory Size: Are They Matched?
Authors: Calder William A.
Published: May 2006

The size—dependence of sound output power has important implications for ecology, behavioral energetics, and physiology. The sound power of 32 species of birds and the areas occupied by individuals of 86 species of birds show quantitative similarity in scaling to body size. This suggests a general matching of sound output power to dimensions of the spatial requirements of a species. Sound output was ±81.3 mW/ha of territory, and was independent of bird size (6—10 800 g). The allometric patterns tend to confirm conclusions from both theory and studies of single species. Caution should be exercised in estimating population densities from transect censuses than depend heavily on call and song, because of possible size—dependent bias in detectability.
Abiotic and Biotic Factors in Litter Decomposition in a Sermiarid Grassland
Authors: Vossbrinck C. R. , Coleman D. C. , Woolley T. A.
Published: May 2006

Decomposition of grass leaf litter was studied on a shortgrass prairie using chemicals (HgCl2 and CuSO4) to prevent microbial activity (abiotic treatment), 53—μm nylon mesh to exclude mesofauna (microbial treatment), and l—mm nylon mesh to allow the access of mesofauna. After 9 months, 15.2% of the blue grama grass litter was decomposed in the microbial treatment, and 29.4% was decomposed in the microbial plus mesofaunal treatment. After 7 months, 6.2% of the litter had disappeared from the abiotic treatment. There was a general decrease in C:N ratios with the microbial treatment lowest at the end of the experiment. Total available carbohydrates generally decreased with time. Certain mite families fluctuated with seasons. The tydeids were most active in winter and tetranychids were most active in summer. A correlation between abiotic factors and mite families was also observed.
Generalization of a Nearest Neighbor Measure of Dispersion for Use in K Dimensions
Authors: Clark Philip J. , Evans Francis C.
Published: May 2006

The 1st, 2nd and 3rd moments of r, the distance to nearest neighbor, are derived so as to generalize for use in k dimensions a measure of spacing based on the ratio of the mean distance observed in a population of known density to the mean distance expected under the assumption of random dispersion. Numerical values of these moments for 1—, 2—, and 3—dimensional space are presented, and significance tests for the difference between observed and expected mean distances are considered.
Thermoregulation and Flight Activity Satyrine, Coenonympha Inornata (Lepidoptera: Satyridae)
Authors: Heinrich Bernd
Published: May 2006

The inornate ringlet butterfly, Coenonympha inornata, is highly constrained by temperature in its activity, and even on sunny days may spend a major portion of its time grounded. Thermoregulation in these lateral baskers can consume the major portion of their time; males alternate between basking and flying, and at 16°C spend 73% of their time basking and only 27% of their time flying. At high ambient temperatures (Ta), on the other hand, they spend most (>80%) of their time in flight. Active butterflies were followed for up to 52 min in the field to determine foraging behavior, mating success, and time investments for thermoregulation. Foraging was a minor component of their flight activity. Most of the flight activity was associated with mate—seeking. Thoracic temperatures were measured in the field on individuals tethered to thermocouples that permitted flight and basking behavior. Basking at low Ta allowed the maintenance of higher thoracic temperatures than could be maintained in continuous flight, and the butterflies then adopted a sit—and—wait strategy in mate chasing. In contrast, at high Ta they used a search strategy for mate seeking instead.
Interactions Between Intraspecific Competition and Predation in an Amphibian Predator‐Prey System
Authors: Morin Peter Jay
Published: May 2006

The predatory salamander Notophthalmus viridescens indirectly facilitates the growth and survival of herbivorous tadpoles of Hyla crucifer, when the latter are embedded in guilds of superior competitors. I used experimental manipulations of N. viridescens and H crucifer densities in artificial ponds to explore the dependence of facilitation on guild composition, by testing whether N. viridescens facilitated H. crucifer when it was the only species in the tadpole guild. I also measured the independent relative contributions of intraspecific competition and predation to tadpole survival and growth, to test whether competition among prey influenced the impact of predation on prey survival. Tadpole survival was independent of intraspecific density and negatively affected by predator density. In communities without predators, increased tadpole densities decreased growth rates, prolonged larval development, and reduced froglet mass at metamorphosis. Predation tended to increase metamorph mass slightly within a given level of initial tadpole density. However, the impact of predators on tadpole survival was independent of density—dependent tadpole growth. Predators failed to reduce competition substantially among larval H. crucifer, because tadpoles altered their microhabitat used to avoid predators. Consequently, tadpole densities and competitive interactions were only slightly moderated by predators. Predator avoidance exacted no cost in terms of reduced mass at metamorphosis or prolonged larval periods. Although predators may greatly reduce the intensity of interspecific competition among prey by reducing densities of particularly susceptible competitively superior species, the intensity of intraspecific competition among remaining predator—resistant species may remain unaffected. The failure of N. viridescens to facilitate H. crucifer in the absence of other species of competing anurans indicated that previously documented facilitation was indirect and dependent on guild structure.
Dominance, Predation, and Optimal Foraging in White‐Throated Sparrow Flocks
Authors: Schneider Kathryn J.
Published: May 2006

White—throated Sparrows (Zonotrichia albicollis) form winter flocks with linear dominance hierarchies. When birds of known dominance rank were presented with feeding sites that varied in distance from cover, individuals demonstrated a preference for the sites near cover over those in more open areas. This preference was reflected in the pattern of food depletion. Furthermore, dominant birds feed near shelter more often than subordinates, since high rank allowed access to preferred sites. Observations suggest that cover provides effective protection from predators. In an experiment to examine the trade—off between energy intake and predation risk, birds presented with food patches at various distances from cover did not feed optimally in terms of energy harvested per unit time. Food was depleted exponentially, and birds nearly exhausted an area before moving farther from cover. The data suggest that White—throated Sparrows reduce the risk of predation at the expense of foraging efficiency.
Operative Environmental Temperatures and Basking Behavior of the Turtle Pseudemys Scripta
Authors: Crawford Kenneth M. , Spotila James R. , Standora Edward A.
Published: May 2006

Operative environmental temperatures (Te, an index of the thermal environment) were measured for basking Pseudemys scripta in South Carolina. Operative environmental temperatures were good predictors of the basking behavior of P. scripta. Turtles in this study generally did not bask unless Te was 28°C (preferred body temperature) or higher. This demonstrated that basking was not a random behavior in respect to Te, and implicated thermoregulation as a major factor eliciting basking behavior. Operative environmental temperature was positively related to short—wave and total solar radition as well as to air and substrate temperature. Substrate temperature was the best single predictor of Te. A multiple regression equation (Te = 0.005R + 0.103Ta — 1.16 log V + 0.932Ts — 2.54, r2 = .90, where R = total radiation in watts per square metre, Ta = air temperature in degrees Celsius, V = wind speed in metres per second, and Ts = substrate temperature in degrees Celsius) defines the relationship of Te to microclimate variables. Movement of the sun through the day results in spatial variation in Te's available to turtles and influences their location and basking behavior.
Area‐Dependent Changes in the Bird Communities and Vegetation of Southern Wisconsin Forests
Authors: Ambuel Bruce , Temple Stanley A.
Published: May 2006

We studied avian biogeography and habitat selection in forests of southern Wisconsin ranging in area from 3 to > 500 ha. Bird diversity in these woodlots increases with area, due primarily to an increase in the number of forest—dwelling, long—distance migrants. We consider two possible explanations for this pattern: (1) area—dependent changes in forest vegetation, or (2) area—dependent change in interactions with competitors, predators, or brood parasites. We first describe vegetation structure and composition, then show that this description comprises important habitat features of forest birds. Bird habitat is characterized in three ways: (1) vegetational structure within bird territories is compared with that at random locations in the same woodlots, (2) structural characteristics of territories of different species are compared, and (3) factors related to species' abundance in different woodlots are analyzed. We found no area—dependent trends in vegetation structure or composition that seem likely to influence the bird community. However, forest—edge and farmland species increase in density as woodlot area decreases. We suggest that forest—edge and farmland species exclude certain forest—dwelling, long—distance migrants from small woodlots, and that this exclusion influences the bird community more than area—dependent changes in habitat or the degree of woodlot isolation.
The Effects of Thirteen Years of Annual Prescribed Burning on a Quercus Ellipsoidalis Community in Minnesota
Authors: White Alan S.
Published: May 2006

A Quercus ellipsoidalis community in central Minnesota has been prescribed burned annually since 1965 in an attempt to restore the area to its presettlement oak savanna structure and composition. By 1979 density and basal area of the overstory were significantly lower in the burned area than in an adjacent unburned area but were still higher than estimated savanna values because of the persistence of stems @>25 cm diameter at breast height (dbh). A tall—shrub/small—tree layer was totally lacking in the burned area but averaged 19% cover in the unburned area. Understory richness was significantly higher in the burned area than in the unburned area. Most of the species that showed a significant difference between the two areas peaked in the burned area; this was especially true for grasses and forbs. These results indicate that annual prescribed burning is gradually restoring the area to savanna but that the restoration is not yet complete. Complete restoration may not be possible with annual burning because such burning seems to have little effect on large—tree (@>25 cm dbh) mortality.
The Estimation and Analysis of Preference and Its Relatioship to Foraging Models
Authors: Chesson Jean
Published: May 2006

This paper summarizes models of estimation and analysis for the measure of consumer food preferences originally derived by Manly et al. (1972) and further developed by Chesson (1978). Unlike many alternative measure this measure of preference does not change with changes in food densities unless consumer behavior also changes. This measure is shown to relate in a simple way to parameters, such as clearance and attack rates, which appear in certain commonly used models of foraging behavior.
Productivity and Density of Soil Algae in an Agricultural System
Authors: Shimmel Stephen M. , Darley W. Marshall
Published: May 2006

Soil algal productivity and biomass were monitored in a conventional tillage agricultural system from December 1981 through December 1982. Productivity was based on the fixation rate of radiolabeled carbon dioxide. Biomass estimates (cell number and volume) were based on cell counts radiolabeled carbon dioxide. Biomass estimates (cell number and volume) were based on cell counts and measurements done with epifluoroscence microscopy. Algal productivity values (measured as carbon fixation) ranged from 0 to 76 mg°m—2°h—1, values for cell number ranged from 5.85 x 108 to 5.19 x 1010 cells/m2 and the volume of cells was between 34.8 and 7540 mm3/m2. Regression analysis indicates that algal productivity was most closely correlated with the product of cell number and light intensity, while a number of cells per square metre was most closely correlated with the product of temperature and moisture. The logarithm of the average volume per cell was inversely correlated with soil moisture and temperature. The percentage of algae present as aggregates was proportional to moisture and the square of temperature. Total annual productivity (as carbon) was estimated to be 39 g/m2.
Responses of Erodium to Varying Microsites: The Role of Germination Cueing
Authors: Rice Kevin J.
Published: May 2006

I examined the role of germination cueing in the dynamics of Erodium botrys and E. brachycarpum populations exposed to localized, spatial variation within Californian annual grasslands. In laboratory trials, germination rates of both species increased significantly in seeds previously exposed to fluctuating temperatures (25—45°C) during dry storage. Temperature fluctuations per se were more important than temperature maxima for increasing germination rates. Light conditions during germination had no significant effect on germination rates. Field trials were also conducted. Summer soil temperature regimes were characterized for three germination microsites of Erodium: (1) under the dense litter of annual grasses, (2) in bare soil, and (3) under mounds created by burrowing pocket gophers. Diurnal fluctuations in soil surface temperature were 17°—51°C on bare soil, 20°—41° under litter, and 18°—35° under gopher mounds. Summer field manipulations examined the rates of release from seed dormancy for buried seeds; both species showed a strong positive relationship between the germination rates and the mean diurnal range of temperatures for each microsite. To examine whether seed germination rates were accurate predictors of the suitability of a site for Erodium colonization, germinated seeds of both species were introduced into each microsite type at the start of the growing season. Emergence rates and survival were significantly reduced in mound microsites; seed output per plant was lower in litter microsites. There was a strong positive relationship between Erodium colonization success, as measured by net reproductive rate, and the mean summer diurnal range of soil temperatures. The accuracy of the cueing response in predicting site suitability was reduced with drought or heavy grazing. The results overall suggest significant adaptive value for germination cueing in both Erodium species.
A More Powerful Test for Dispersion Using Distance Measurements
Authors: Johnson Roger B. , Zimmer William J.
Published: May 2006

A new index of dispersion I is proposed. I is based on distance measurements, has computable moments, and is asymptotically normal under the important pattern assumptions. I also provides a test for dispersion. The power of the I test and the asymptotic relative efficiency were computed with respect to two previously proposed tests for dispersion. It was found that the test based on I is more powerful than the other tests for several alternative hypotheses. In addition, I is easily extendable and applicable to m dimensions, whereas other indices and tests relate only to two dimensions.
Independent Evaluation of A Bioenergetics Model For Largemouth Bass
Authors: Rice James A. , Cochran Philip A.
Published: May 2006

We evaluated a bioenergetics model for largemouth bass, Micropterus salmoides, using independent field data on temperature, feeding, and growth of bass in Lake Rebecca, Minnesota. Model predictions of body mass based on observed temperatures and daily ration estimates fell within 2 SE of observed mean body masses on seven of nine sampling dates over a 4—mo period. We employed three statistical methods to evaluate the fit between predicted and observed growth. A lack—of—fit test detected no significant lack of fit between simulated and observed body masses; partitioning mean squared error showed that 76% of the variance was due to random variation rather than to systematic errors, and a reliability index indicated agreement between predicted and observed masses within a factor of 1.12. Growth simulations were relatively robust with respect to simulated errors in the input variables temperatures and swimming speed, but were sensitive to errors in initial body mass. The model used to observed growth to predict cumulative food consumption over the sampling season; the prediction was within 8.5% of an extrapolation from field data. Estimation of consumption rate as a constant proportion of maximum ration for the whole season was shown to be inappropriate; however, three intervals that used different constant proportions of maximum ration fit the data and corresponded to observed changes in bass diet.
Comparative Water Relations of Phreatophytes in the Sonoran Desert of California
Authors: Nilsen Erik Tallak , Sharifi M. Rasoul , Rundel Philip W.
Published: May 2006

The seasonal and diurnal water relations were compared among six desert phreatophytes, two evergreen shrubs, and one deciduous shrub. All species were located in one wash woodland in the Sonoran Desert of southern California. There are several mechanisms by which these Phaenicia have adapted to the desert environment. One group of winter—deciduous phreatophytes (Olneya tesota, Prosopis glandulosa, and Acacia greggii) experienced summer midday leaf water potentials below —4.0 MPa. These phreatophytes had a series of physiological mechanisms for tolerating summer water stress, including seasonal and diurnal osmotic adjustment and the maintenance of high leaf conductance at low leaf water potential. Osmotic adjustment of these three phreatophytes was similar to or greater than that of two evergreen species (Larrea tridentata and Simmondsia chinensis). Dalea spinosa, a stem—photosynthetic phreatophyte, avoided water stress by maintaining a very small leaf area. The summer—deciduous phreatophytes (Hyptis emoryi, and Chilopsis linearis) demonstrated mechanisms of drought avoidance such as change in leaf biomass and low summer leaf conductance. Little osmotic adjustment occurred in the summer—deciduous phreatophytes. The phreatophytic species studied in this investigation have evolved adaptations to water stress that are similar to those of deciduous and evergreen shrubs of the Sonoran Desert. Desert phreatophytes are a complex group of species with varied adaptive mechanisms to tolerate or avoid drought and should not be considered simply as a group of species that avoid desert water stress by utilizing deep ground water unavailable to other desert species of drought tolerance and avoidance.
Partial Inhibition of In Vitro Pollen Germination by Simulated Solar Ultraviolet‐B Radiation
Authors: Flint Stephan D. , Caldwell Martyn M.
Published: May 2006

Pollen from four temperature—latitude taxa were treated with UV radiation in a portion of the UV—B (280—320 nm) waveband during in vitro germination. Inhibition of germination was noted in this pollen compared to samples treated identically except for the exclusion of the UV—B portion of the spectrum. Levels similar to maximum solar UV—B found in temperature—latitude areas failed to inhibit pollen germination significantly, while levels similar to maximum solar UV—B found in equatorial alpine locations caused partial inhibition of germination in three of the four taxa examined.
A Theory on the Temporal Pattern of Operational Sex Ratio: The Active‐Inactive Model
Authors: Iwasa Yoh , Odendaal Francois J.
Published: May 2006

A game model is presented that explains a schedule of male reproductive activity during the breeding season. The main assumptions are: reproductively active males wait for females in a mating arena; females arrive when they are ready to mate; each female mates with a single male, and then leaves; all males are reproductively active on a given day have the same chance of mating with available females; each time is not reproductively active every day, but alternates between sexual active and inactive states; active males have a higher daily mortality than inactive males; and each male chooses daily whether it will be reproductively active or inactive, thereby maximizing its lifetime mating success. The Nash equilibrium of this noncooperative differential game is solved by using dynamic programming. The number of active males each day during the season can be calculated if the female arrival schedule, mortalities of active and inactive males, and annual survivorship of males are given. The model predicts that (1) the numbers of active males and fertilizable females will be correlated if the number of arrivals of fertilizable females varies among days; (2) the operational sex ratio (the ratio of reproductively active males to fertilizable females) decreases through the season; (3) the rate of decrease in the operational sex ratio during the early part of the season is the same as the mortality rate of inactive males; and (4) the operational sex ratio fluctuates during the later part of the season and increases toward the end of the season. A possible application of this model and the relation of the model to other theories on the life—history strategies are discussed.
Genetic and Environmental Contributions to Geographic Variation in the Ovipositor Length of a Cricket
Authors: Mousseau Timothy A. , Roff Derek A.
Published: May 2006

Females of many insects posses an ovipositor, which in crickets is usually used to place eggs deep into the soil. Ovipositor length in female striped ground crickets (Allonemobius socius) increased at higher latitudes and altitudes in North America, despite an opposing trend in overall body size. Crickets inhabiting regions with short growing seasons and long, cold winters invariably had longer ovipositors than crickets inhabiting warmer regions. The only exception to this observation was for first generation crickets in bivoltine populations where there was no pattern of geographic variation in ovipositor length. However, second generation females from these same populations always had longer ovipositors than their first generation ancestors,and followed a pattern of geographic variation similar to that found for univoltine crickets. Overall, these results support Masaki's (1986) model, which predicts that longer ovipositors will evolve in northern cricket populations as an evolutionary response to the selective advantages of overwintering eggs being oviposited deep in the soil in cold habitats. In order to determine the mechanisms underlying patterns of phenotypic variation in the wild, and to test the hypothesis that interpopulation variation reflects genetic differentiation while intergeneration variation within a population reflects environmentally induced phenotypic plasticity, crickets from eight populations were brought to the laboratory and reared through three generations in a common garden. It was found that laboratory—reared populations varied significantly in ovipositor length, with the pattern of variation mimicking that found for field—collected crickets. This finding supports the hypothesis that geographic variation in the wild has a significant genetic basis. The influence of environment on ovipositor length was examined in 20 full—sib families from a bivoltine population. Crickets reared in "autumn—like" conditions (30°C, 15:9 h, L:D), such as might be experienced by second generation bivoltine crickets in the wild, were generally larger and had significantly longer ovipositors than siblings reared under "spring—like" conditions (27°C 11:13 h, L:D). This pattern corresponds to that observed for bivoltine populations in the wild and suggests the importance of environmental cues for phenotypic plasticity, or polyphenism in ovipositor length in bivoltine populations of this cricket.
Selective Herbivore Increases Biomass of Its Prey: A Chiton‐Coralline Reef‐Building Association
Authors: Littler Mark M. , Littler Diane S. , Taylor Phillip R.
Published: May 2006

The intimate association between a selective herbivore (the chiton Choneplax lata) and its primary prey (the crustose coralline alga Porolithon pachydermum) results in increased biomass and accretion of the alga. This process, over ecological and geological time scales, comprises a major component of Caribbean reef—building systems. Manipulative experiments showed that as the chiton grazes the alga it stimulates new meristematic activity and removes sporlings of the competitively superior frondose and filamentous algae, thereby increasing the survival rate of P. pachydermum on the intertidal reef crest. Furthermore, in the absence of C. lata, overgrowths of frondose and filamentous epiphytes provide an attractive food source for parrotfishes (Scaridae), which accelerates bioerosion of the coralline reef—crest structure due to the deep rasping action of feeding activity. Algal removal experiments suggest that the role of P. pachydermum is to provide a predictable food source and refuge substratum, which increases survivorship of the burrowing chiton by minimizing expenditure of energy during foraging and risk of predation. The chiton/coralline alga association is abundant throughout tropical western Atlantic islands and augments reef—building processes on the shallow algal crest portion of Caribbean reefs. Cover of the Choneplax/Porolithon association in the Belize Barrier Reef crest averages 13% (maximum to 70%) with a mean chiton density of 664 individuals/m2 within the association. On average, the extensive networks of interconnected chiton burrows extend between 6 and 10 cm deep and contain one C. lata for every six openings, with the majority of animals (66%) ranging from 16 to 30 mm in length. Gut contents of the chiton consist predominantly of P. pachydermum (51%), followed by bacterial detritus (30%), Cyanophyta (13%), Bacillariophyta (3%), and fleshy microalgae (3%). The close SEM (scanning electron microscope) match between radular morphology of C, lata and grazing scars on the thallus surface of P. pachydermum shows how the chiton regularly feeds on the coralline alga without causing mortality. Virtually all P. pachydermum in the vicinity of C. lata burrows contain radular tract scars of °10 @mm in depth, whereas the photosynthetic meristematic, and reproductive tissues of coralline lie below 20 @mm. P. pachydermum under intense chiton grazing is photosynthetically competent with 0.1 mg C fixed°g—1 organic dry mass°—1, which is not significantly different from ungrazed material and within the range of rates for other crustoe coralline algae. The result is continuous net accretion at a mean rate of 2.3 mm/yr.
Boundary Form Effects on Woody Colonization of Reclaimed Surface Mines
Authors: Hardt Richard A. , Forman Richard T. T.
Published: May 2006

Woody plants and evidence of browsing were measured on eight reclaimed strip mines in Maryland and West Virginia to see whether revegetation patterns differed adjacent to concave, straight, and convex forest boundaries. Two clonal species predominated (Rubus allegheniensis and Robinia pseudoacacia), followed in abundance by three wind—dispersed species (Fraxinus americana, Acer rubrum, Betula lenta), and a variety of animal—dispersed species. Mine transects adjacent to concave forest boundaries had 2.5 times as many colonizing stems as those next to convex boundaries. Stems of colonizing species extended >61 m from concave boundaries, but rarely > 13 m from convex boundaries. Stem density of all the common animal—dispersed species was correlated with their abundance in the adjacent forest edge, whereas no relationship existed for Robinia or the wind—dispersed species. Evidence of browsing was greater adjacent to concave boundaries than opposite convex boundaries. These strikingly different colonization patterns appear to be primarily the result of the immigration process interacting directly with shape as a spatial characteristic. Through time, a "concave—convex reversal" in boundary form is evident. This results from a "cove concentration effect" where the greatest boundary expansion rate is in coves being colonized. Almost all patterns next to straight boundaries were intermediate between those opposite concave and convex boundaries. We conclude that boundary form may exert a powerful control over adjacent ecosystems in a landscape. This presents significant opportunities for planning and managing surface mines and other colonizing areas.
Belowground Carbon Allocation in Forest Ecosystems: Global Trends
Authors: Raich J. W. , Nadelhoffer K. J.
Published: May 2006

Carbon allocation to roots in forest ecosystems is estimated from published data on soil respiration and litterfall. On a global scale, rates of in situ soil respiration and aboveground litter production are highly and positively correlated, suggesting that above— and belowground production are controlled by the same factors. This relationship also allows us to predict rates of total soil respiration and total carbon allocation to roots in forest ecosystems from litterfall measurements. Over a gradient of litterfall carbon ranging from 70 to 500 g°m—2°yr—1, total belowground carbon allocation increases from 260 to 1100 g°m—2°yr—1. The ratio of belowground carbon allocation to litterfall decreases from 3.8 to 2.5 as litterfall carbon increases from 70 to 200 g°m—2°yr—1, but changes little (2.5 to 2.2) as litterfall carbon increases from 200 to 500 g°m—2°yr—1. Use of this relationship permits the construction of simple carbon budgets that can be used to place upper limits on estimates of fine root production in forest ecosystems. Determining live—root respiration rates in forest ecosystems will further constrain the range of possible root production rates.
Lindeman's Contradiction and the Trophic Structure of Ecosystems
Authors: Burns Thomas P.
Published: May 2006

R. L. Lindeman's empirically based generalizations that both progressive efficiencies and percent of energy lost due to respiration increase with trophic level appeared contradictory, because he linked trophic levels in series to form a simple trophic chain. This model equates the energy not respired by the populations aggregated to form a trophic level to the productivity of the populations assigned to the next trophic level. This is clearly not the case for Cedar Bog Lake and ecosystems generally, because of nonpredatory losses and energy gains from other than the previous step in the trophic chain, e.g., bacterivory, detritivory, and feeding on organisms at more than one trophic level. Network analyses of energy—flow models make possible an objective and unambiguous definition of trophic level that does not suffer this contradiction. Trophic guild is proposed as an alternative to trophic level when is meant is an aggregation of species with similar trophic resources.
Species‐Area Relationship for Stream Fishes
Authors: Angermeier Paul L. , Schlosser Isaac J.
Published: May 2006

We sampled riffles and pool habitats of small streams in Minnesota, Illinois, and Panama to examine variation in species—area relationships within and between the respective fish faunas. For six of the seven steams studies, habitat lume was a better predictor of species richness than was habitat area, and number of individuals was a better predictor of species richness than habitat volume. Slopes of species–volume relationships were similar among regions, but the number of species per unit volume was greater in Panama. Multiple regression analyses indicated that knowledge of habitat complexity and volume did not enhance appreciably the capability of linear models to predict species richness from number of individuals in the sample. These results support the hypothesis that species—area relationships may often be epiphenomena stemming from the more comprehensive community "samples" intercepted by larger habitat patches. Although number of individuals was the best single predictor of species richness, habitat structure and type clearly influenced species' distributions in some streams, thereby indicating that species—area relationships were not strictly sampling phenomena. An index of habitat complexity based on depth, current, and bottom type was correlated with species richness in two Panama streams. Also, the abundance of individual species was more likely to be correlated with habitat volume in Panama than in Illinois or Minnesota, and species relative abundances were more similar between years in Panama than in Illinois or Minnesota streams, especially in pools. These patterns suggest that in streams subject to strong seasonal and annual environmental variation, habitat features are poorer predictors of fish distribution and abundance than in streams subject to less environmental variability. We speculate that annual variability in reproductive success and harsh winters interact to maintain imbalance between the fish assemblages and their habitat in Minnesota. Weak relationships between species richness and habitat volume or complexity may be indicative of population variability and the predominance of extinction/recolonization processes in community organization.
Growth‐Mortality Trade‐Offs and the Evolution of Juvenile Life Histories in the Alcidae
Authors: Ydenberg R. C.
Published: May 2006

The juvenile life history of each of the 22 living species in the avian family Alcidae is composed of a period in the nest followed by a move to the ocean (fledging), where development is completed. The age, degree of development, and the mass of the alcid chick at fledging are extraordinarily variable, both between and within species. The available information suggests that nests are safe places (the daily mortality of chicks there is low) relative to the ocean, but that growth in the nest is slow relative to that attainable at sea, because of the parental travel time between the nest and feeding areas. The chick therefore faces a trade—off in deciding when to make the transition from nest to ocean. A dynamic programming model incorporating (1) the differential growth and mortality in the nest and ocean habitats, and (2) assumptions about the relation between size and survival, accurately predicts the fledging age and mass of the Common Murre (the only species for which reasonable estimates are available). The model suggests explanations for some other phenomena associated with the reproduction of alcids and other northern seabirds, namely the seasonal decline in mass at fledging, and the negative relation of mean fledging age and mass observed between colonies in several species. The optimal fledging policy is also considered from the point of view of the parents. There are many indications that visits to the nest endanger the parents' lives, and hence parents should be @`reluctant" provisioners, leading to conflict between parents and their offspring. This evolutionary conflict and its implications forour understanding of avian life histories are discussed.