bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Food Quality on Growth of a Stream Detritivore, Paratendipes Albimanus (Meigen) (Diptera: Chironomidae)
Authors: Ward G. Milton , Cummins Kenneth W.
Published: May 2006

Laboratory—determined larval growth rates of the detritivore (collector—gatherer) Paratendipes albimanus (Chironomidae) responded proportionally to the microbial densities of 4 food sources. Substrates with higher microbial activities and biomasses produced greater growth rates in the order: pignut hickory (Carya glabra) leaves > white oak (Quercus alba) > insect feces > natural stream detritus. Laboratory growth rates of P. albimanus were linearly related to quantitative estimates of food quality based on substrate adenosine triphosphate (ATP) and respiration rates but were not statistically related to total N or C. Although P. albimanus is univoltine in Augusta Creek, Michigan, an experimental laboratory population of first—instar larvae completed a 2nd generation during the summer when fed detritus generated from hickory leaves. A second experimental population failed to develop past the first instar when fed natural detritus. The natural growth pattern of P. albimanus involves the interaction of temperature and food quality.
The Midsummer Dynamics of Two Daphnia Species in Wintergreen Lake, Michigan
Authors: Threlkeld Stephen T.
Published: May 2006

During 1976, midsummer reductions in densities of Daphnia pulicaria and Daphnia galeata mendotae populations occurred in Wintergreen Lake, Michigan. Previous attempts to determine the causes of such declines have indicated correlations between predator populations, the presence of unpalatable algae or high midsummer water temperatures, and the reduction or disappearance of the daphnid populations. In this study, in situ life table experiments were performed to assess the influence of natural food and temperature conditions on population growth. A weekly sampling program showed that D. pulicaria was dielly concentrated, after early summer, at depths between the anaerobic hypolimnion and the warmer epilimnion, consistent with previous information indicating it to be a cold—water species. However, in situ life table data showed that D. pulicaria was capable of surviving in epilimnetic water up to 27°C, although reproduction was greatly reduced for a 6—day period in mid—July. This reduction in reproduction appeared to be the result of an interaction of high temperatures, declining standing crops of small algae and increasing amounts of Anabaena, Ceratium and Volvox. Daphnia galeata mendotae did not show any adverse response to these mid—July algae—temperature conditions. Analysis of predator gut contents suggested that both daphnids were heavily preyed upon by bluegills (Lepomis macrochirus). Shifts in the size structure of the daphnid populations were also consistent with intense size—selective predation by bluegills, as was the tendency for the age distribution of parthenogenic eggs to become skewed to younger eggs as the midsummer decline proceeded. Differences in body size, ephippial production and habitat preferences between the 2 species are also consistent with the hypothesis that planktivory is a strong selective force in their evolution.
Comparative Demography of Pikas (Ochotona): Effect of Spatial and Temporal Age‐Specific Mortality
Authors: Smith Andrew T.
Published: May 2006

The structure of 4 populations of a small boreal mammal, the pika (Ochotona princeps), is examined to explore the causal mechanisms of evolution of life—history features of the species. Litter size reflects potential and realized fecundity and is largest at Bodie (low latitude, low altitude), intermediate at Sierra and Colorado (low latitude, high altitude), and smallest at Alberta (high latitude). The age specificity of mortality largely determines the number of sites available for settlement by juveniles, which dictates the feedback to liter size. Populations are stable and habitats continuously saturated at Alberta; mortality of adults is predictable. The Sierra and Colorado sites possess unstable population. At these sites, snowmelt in spring (the harbinger of emergent vegetation and successful weaning) is relatively unpredictable compared to Alberta; adult mortality may be high in years of early or late snowmelt. The unpredictability also selects for asynchronous breeding such that more sites are available in any one year to offspring from certain successfully weaned litters. The habitat at Bodie is temporally and spatially unsaturated. Largely because of poor vagility of pikas, much of the habitat is vacant. Colonization is unable to completely offset extinction of populations on patches of habitat. Here, the selective factor determining litter size is juvenile production and not adult mortality.
Brood Size and the Use of Time and Energy by the Phainopepla
Authors: Walsberg Glenn E.
Published: May 2006

Time and energy budgets were calculated for 16 Phainopeplas (Phianopepla nitens) nesting in the coastal woodlands of southern California. Brood size differed 50%; 4 pairs raised 3 young and 4 pairs raised 2 young. Compared to pairs feeding 2 nestlings, pairs feeding 3 nestlings spent an average of 42% more time flycatching, 16% more time foraging at fruiting shrubs, and 22% more of their active day in flight. Daily energy expenditure of pairs feeding 3 nestlings was increased a surprisingly small amount compared to that of pairs feeding only 2 young–a mean of 7%, or 12 kJ. Over the entire period from egg synthesis to fledging, total parental energy expenditure is estimated to increase only 4.7% associated with a 50% increase in brood size. The Phainopepla may exhibit a unique annual cycle; it apparently breeds twice annually, once in its summer range (where the present study was conducted) and once in its winter range in the Sonoran Desert. Using data from this study plus those from a previous one, the 2 breedings were compared in terms of parental energy expenditure from egg—laying until fledging and parental harvesting requirements during the incubation and nestling periods. (Harvesting requirements = parental energy expenditure + the energy requirements of any young being fed.) Remarkable convergences are seen in the reproductive energetics of Phainopeplas breeding in the 2 habitats. Regardless of the striking differences between the 2 seasonal ranges in parental energy expenditure, habitat, daylength, and social system used, a Phainopepla incubating or feeding 2 nestlings in the coastal woodlands has a mean harvesting rate (kilojoules/hour active) virtually identical to that of a bird in a comparable stage of breeding in the desert. Similarly, total parental energy expenditure from egg synthesis until fledging averages only 2.6% different between populations breeding in the 2 areas, when calculated on an energy expended per young fledged basis.
The Influence of Food and Water on Growth Rates in a Tropical Lizard (Anolis Aeneus)
Authors: Stamps Judy , Tanaka Sanford
Published: May 2006

The limiting effects of food and water on juvenile growth rates in the lizard Anolis aeneus were investigated in the field (Grenada, West Indies) and laboratory. Growth rates of lizards in the field were unrelated to their snout—vent lengths, but both prey biomass and rainfall had significant effects on juvenile growth rates. Laboratory experiments indicated that water had a primary limiting effect on growth; even when food supplies were superabundant, growth rates were low when drinking water was curtailed. Laboratory and field experiments suggest that limited water availability reduces growth rates for most (67%) of the dry season, whereas food levels are sufficiently low to limit growth during the weeks of the dry season when rainfall is sufficient for growth. During the wet season there is no evidence of water scarcity, food levels are high and average growth rates are 85% of the maximal rates observed under optimal conditions in the laboratory.
Life History Significance of Size‐Triggered Metamorphosis in Milkweed Bugs (Oncopeltus)
Authors: Blakley Nigel
Published: May 2006

Achievement of a critical body size provides the proximate stimulus for the metamorphic molt in Oncopeltus and other hemimetabolous and holometabolous insects. Effects of size—dependent stimuli on metamorphosis vary in detail among different insects, although the adaptive significance of this variation is as yet unknown. The phenomenon is important to life histories where growth rates are highly variable, since it allows larvae to delay eclosion until a prerequisite body size is attained. In Oncopeltus, variation in growth rate occurs where nymphs develop on individual host plants which differ greatly in nutritional quality, depending on the presence or absence of seeds. This variation in growth rates results in marked variation in adult size. The size at which nymphs eclose is determined by opposing selective forces in the adult and larval stages. When growth is slow, nymphs which must attain a larger size exhibit longer developmental times and lower survival to eclosion. However, bugs which eclose at a larger adult size survive longer under starvation conditions, and presumably could disperse for longer periods in search of food sources. This is particularly important for females eclosing on nonfruiting plants, since they must locate a supply of seeds before reproduction can commence.
Sexual Dimorphism in Bullfrogs
Authors: Howard Richard D.
Published: May 2006

Data on body size, age/size at sexual maturity, and adult survival were obtained between 1975 and 1978 for a population of bullfrogs, Rana catesbeiana, at the E. S. George Reserve of the University of Michigan. Both males and females continued to grow when adults; older individuals were often 50% larger than newly matured individuals. No sexual differences in adult growth rate were observed, but data on average and maximum adult body size indicated that females were significantly larger than males during each year of the investigation. The discrepancy between these measures resulted from sex—specific differences in adult age distribution: males matured at earlier ages and/or smaller sizes than females, and large males suffered higher mortality than large females. Such life history differences between the sexes can in turn be related to patterns of mating effort and parental effort. Apparently, selection for mating effort in males to defend territories and parental effort in females to produce large clutches has resulted in sexual maturation at different ages but in similar advantages of large body size. The influence of mating effort and parental effort on sexual dimorphism is discussed for other anuran species as well as birds and mammals. It is suggested that an observed body size dimorphism in any species in which individuals grow appreciably as adults could result from a difference in the age distributions of males and females as well as from differential growth rates.
Observations on Stream Minnows in a Patchy Environment: A Test of a Theory of Habitat Distribution
Authors: Fraser Douglas F. , Sise Thomas E.
Published: May 2006

The seasonal habitat use and movement patterns of juvenile and adult Semotilus atromaculatus and Rhinichthys atratulus, two stream—dwelling cyprinids, were studied for a period of 2 yr in a small headwater stream. The responses of the fish to the patchy habitat were used to test a prediction of the Fretwell—Lucas Theory of Habitat Distribution, namely that populations tend to become more uniformly distributed over habitat patches as population size increases. Marked individuals executed complex movement patterns which were species, age, and season dependent. Although all age classes of both species were able to move among all habitat patches, adult S. atromaculatus were clumped at high densities, while adults of R. atratulus and juveniles of both species conformed to the prediction of the theory. The clumping behavior observed at low population densities is discussed as a possible adaptation to ambush predation.
Experimental Acidification of a Stream in the Hubbard Brook Experimental Forest, New Hampshire
Authors: Hall Ronald J. , Likens Gene E. , Fiance Sandy B. , Hendrey George R.
Published: May 2006

Incident precipitation in the northeastern United States averages about pH 4 as a result of increased pollution from sulfuric and nitric acids. To determine the effect of this increased acidity on the ecology of aquatic ecosystems, dilute concentrations of sulfuric acid were added to Norris Brook, a stream in the Hubbard Brook Experimental Forest, West Thornton, New Hampshire, USA. The stream was maintained at pH 4 from April to September 1977. With increased acidity stream water concentrations of Al, Ca, Mg, K, and probably Mn, Fe, and Cd were elevated; no change in dissolved organic carbon (DOC), Na, NO3 NH4, Ni, Pb, Cu, or Zn occurred at the lower pH. Emergence of adult mayflies (Ephemeroptera), some stoneflies (Plecoptera), and some true flies (Diptera) decreased at the lower pH. Larger numbers of immature aquatic invertebrates in the collector, scraper, and predator functional groups were found in drift samples from the experimental are during the 1st wk after acid addition. After the 1st wk of increased acidity total numbers of organisms drifting in the experimental area were similar to values obtained in the reference area. Emergence of adult collectors and invertebrate density in the benthos decreased in the treatment area. Periphyton biomass increased at the low pH, but hyphomycete fungal densities decreased. A basidiomycete fungus increased in the experimental area relative to the reference section. Brook trout showed no morphological signs of stress at the low pH. Stream acidification decreased species diversity, increased representation of community dominants, and decreased the complexity of the food web.
Harmonic Mean Measure of Animal Activity Areas
Authors: Dixon Kenneth R. , Chapman Joseph A.
Published: May 2006

A new method of calculating centers and areas of animal activity is presented based on the harmonic mean of an areal distribution. The center of activity is located in the area of greatest activity; in fact, more than one “center” may exist. The activity area isopleth is related directly to the frequency of occurrence of an individual within its home range. The calculation of home range allows for the heterogeneity of any habitat and is illustrated with data collected near Corvallis, Oregon, on the brush rabbit (Sylvilagus bachmani.)
Multiple Stable Configurations in Ordination of Phytoplankton Community Change Rates
Authors: Allen T. F. H. , Bartell Steven M. , Koonce Joseph F.
Published: May 2006

Relationships between a phytoplankton community and its environment were found by multivariate analysis of not species occurrences but rather the first difference of species weekly occurrences. Principal component analysis of 55 sample first differences in a 103—dimensioned species first—difference space was performed. Successive sample points described a community trajectory in first difference ordination space. This trajectory oscillated in several discrete ordination regions. The discrete regions of oscillation were first defined subjectively but between—region discontinuities were verified by reconstruction according to simple objective criteria. The regions of oscillation are taken to represent centers of community structure in multivariate species first difference space. Similar patterns of oscillation found in an ordination in environmental state space were likewise interpreted as centers of multivariate environmental structure. The objectively defined discontinuities on the environmental ordination show close correspondence to those on the community ordination. There are structural forces intrinsic to the community, and the community composition moves from one center of community structure to another only by the intervention of intermittent shift in environmental structure. The shifts in the environment were indicated by the principal component analysis of estimates of the state of nine environmental parameters.
Effects of Ammophila Arenaria on Sand Dune Arthropod Communities
Authors: Slobodchikoff C. N. , Doyen John T.
Published: May 2006

Ammophila arenaria, a grass commonly used to stabilize loose sand, disrupts the structure of sand dune arthropod communities. Total numbers of arthropods are related to percent cover of A. arenaria by a hypocycloid function, so that even low percentages of the grass cover strongly depress arthropod populations. Species area curves (plotted logarithmically) have consistently steeper slopes on dunes supporting A. arenaria, indicating fewer species and a smaller number of rare species than on natural dunes. Species (dominance) diversity of arthropods declines in an inverse linear fashion as the density of A. arenaria increases. In contrast, dune stabilization by native plants increases arthropod diversity and numbers.
Seedling Establishment of Ferocactus Acanthodes in Relation to Drought
Authors: Jordan Peter W. , Nobel Park S.
Published: May 2006

The 30 smallest seedlings of Ferocactus acanthodes (Lem.) Britton & Rose (Cactaceae) at a canyon site in the northwestern Sonoran desert average 2.5 cm in height. Based on field studies of CO2 exchange throughout the year, the estimated time of their germination was late summer 1976. To explain why so little establishment occurred in recent years, the length of lethal drought for seedlings of various ages was calculated from the seedling geometry (volume—to—surface ratio), dehydration tolerance, and transpiration rates. Individual years were identified which had sufficiently long growing seasons relative to the length of the subsequent droughts to allow establishment. Eight of the last 18 yr were found to be suitable for establishment of F. acanthodes, the last year being 1976.
Seasonal Change in Guild Structure: Oak Woodland Insectivorous Birds
Authors: Wagner Judith L.
Published: May 2006

The use of foraging sites by a foilage— and bark—gleaning guild of insectivorous birds was studied for 2 yr in a California oak woodland. Choices of plant types, perch size, and foraging height are presented for both residents and migrants in two contrasting seasons (fall/winter and spring). Seasonal differences were fewer than differences between years at the same season. Niche breadths and overlaps of residents in the 2nd yr of the study were mostly larger in spring than in fall/winter, although the contrasts were not statistically significant. The niche breadth findings are viewed as consistent with a prediction of optimal foraging theory that a broader range of patch types will be used when food is abundant. Dendrograms based on niche overlaps for fall/winter and spring showed that three resident species (Chestnut—backed Chickadee, Plain Titmouse, and Hutton's Vireo) constituted the core of the guild, together with two migrants in fall/winter (Ruby—crowned Kinglet and Yellow—rumped Warbler) and one in spring (Blue—gray Gnatcatcher). The foraging of residents was not influenced by the presence of different migrants at different seasons. Species most similar in foraging sites were distinct in bill size or behavior, except for the chickadee and the vireo. These two species are viewed as potential competitors.
Patterns of Microhabitat Occupation of Six Closely Related Species of Mosses Along a Complex Altitudinal Gradient
Authors: Watson Maxine A.
Published: May 2006

Patterns of microhabitat occupation were studied for six species of closely related mosses along a complex altitudinal gradient spanning 1600 m on the northeast face of Mount Washington, New Hampshire, USA. Differential patterns of distribution were noted among species along the axes of percent incident light, substrate type, soil texture and soil pH. The ecotope breadths of Polytrichastrum species were approximately double the ecotope breadths of Polytrichum species. Factors capable of producing ecotope separation among Polytrichum species were insufficient for achieving ecotope separation among Polytrichastrum species. The observed patterns suggest that the two genera have evolved in different ways to achieve separation among species. Evidence for competition regulating the relative distribution of these six species was weak. In general, overlap increased with increased in co—occurrence of particular species pairs. Ecotope breadths were unaffected by the presence of closely related species. Species were packed more closely along dimensioned axes than is predicted by competition theory. The problems of interpreting overlap indices as indices of competition intensity are discussed.
The Home Range: A New Nonparametric Estimation Technique
Authors: Anderson D. John
Published: May 2006

A new technique for estimating home range size from a sequence of independent observations of animal positions is introduced. This method describes home range in a probabilistic sense, makes no assumption about the underlying distribution, and therefore is nonparametric. The procedure is based upon an existing nonparametric technique for density estimation which uses the Fourier transform (Tarter and Kronmal 1970). A comparison is made with two commonly used methods; the minimum convex polygon method (Southwood 1966) and bivariate normal method (Jennrich and Turner 1969), as well as another recent nonparametric method developed by Ford and Krumme (1979). All these methods have certain problems, making none of them suitable for every situation. The trade—offs among these methods and some fundamental limitations of home range estimation are discussed. Evidence is given which indicates that in some situations the proposed method is preferable to earlier methods.
Timing of Reproduction by Predatory Stinkbugs (Hemiptera: Pentatomidae): Patterns and Consequences for a Generalist and a Specialist
Authors: Evans Edward W.
Published: May 2006

The seasonal timing of reproduction was examined for two predatory stinkbugs (Hemiptera: Pentatomidae) in stands of goldenrod (Solidago spp.) near Ithaca, New York, USA. One species, Perillus circumcinctus, is a specialist predator of soft—bodied beetle larvae and occurs in few habitats. The second species, Podisus maculiventris, is a generalist predator that attacks many kinds of insect prey in a great diversity of habitats. In goldenrod stands both predators fed primarily on Trirhabda spp. (Coleoptera: Chrysomelidae). Sweep samples revealed that nymphs of the specialist predator matured in synchrony with larvae of the univoltine Trirhabda in May and June. Most nymphs of the generalist predator matured several weeks later and older instars of this predator fed primarily on Trirhabda adults. Nymphs of both predators easily overpower larvae of Trirhabda, but they rarely succeed in capturing the alert beetle adults; consequently the availability of food in goldenrod stands deteriorates as the beetles mature. Field patterns of body size of the predators reflect the seasonal change in food supply. For both predators, adult body size depends upon the rate at which nymphs consume prey. As the season progressed, the size of newly molted adults of both stinkbugs declined, paralleling the earlier decline in availability of Trirhabda larvae as prey for nymphs. Because of differences in seasonal appearance, most specialist predators attained adult sizes in the field approximating the maxima attained in the laboratory, while most generalist predators attained significantly smaller sizes. Those few generalist predators that did mature early also generally attained maximum size; they experienced little difficulty finding, capturing, and digesting Trirhabda larvae. These results indicate that the specialist predator exploits Trirhabda populations more effectively that the generalist. The key difference in the habits of the two predators lies not in the foraging efficiency of nymphs nor in biochemical adaptation to the prey, but rather in timing of reproduction. Well—timed oviposition in goldenrod stands by specialist females ensures that offspring mature during the short period each summer when prey are easily harvested. In contrast, the relatively poor timing of oviposition by generalist females results in most of their offspring experiencing substantial food stress.
Contrasting Strategies of Gamogenesis in Northern and Southern Populations of Cladocera
Authors: Sebens David G.
Published: May 2006

In the northern United States, winter constitutes the chief environmental stress for Cladocera, which anticipate this by entering an intensive and coordinated period of gamogenesis in autumn. Hatching of the resulting resting eggs in spring reestablishes those populations that had died back over winter. At extreme conditions, few or no species remain active over winter, but in progressively milder winter conditions southward, more and more species not only remain active after autumnal gamogenesis but even continue some parthenogenetic reproduction throughout the winter. Toward the south the period of autumnal gamogenesis of these "northern" species becomes gradually less intensive and coordinated and eventually is virtually eliminated. Instead, gamogenesis now tends to occur in spring in Louisiana—Mississippi and Florida, suggesting a shift in the season of major stress for these species from winter to summer. Many of these "northern" species tend to die out in summer or at least become greatly reduced in numbers, possibly because of too high temperatures. Other species, which are mostly very small, tend to take over these water bodies in summer. As they have chiefly sourthern distributions, they are referred to collectively as "southern" species. They tend to become gamogenetic in autumn, and over winter they either disappear completely or else are reduced to very low numbers. Thus, water bodies in florida and the near—coastal region of the Gulf of Mexico tend to be occupied seasonally by two quite different assemblages of Cladocera, a "northern" assemblage in winter, spring, and early summer, which tends to become gamogenetic in spring, and a "southern" assemblage in summer and autumn which tends to become gamogenetic in autumn. Gamogenesis in the south, whether in spring or autumn, is not so well coordinated as autumnal gamogenesis in the north, and with few exceptions it is sporadic and not intensive. The data tends suggest, however, that for natural populations in the south gamogenesis among "northern" species peaks in April to mid—May and among "southern" species in October—November. For the strictly vernal species, gamogenesis tends to occur in March. Still further south in the tropics, gamogenesis occurs very irregularly at low levels of intensity and seemingly without coordination among species and unrelated to any particular season. The resting eggs produced thereby are regarded as insurance against low—probability events that could otherwise eliminate the populations and as a means of continually introducing new genotypes into the population, thereby facilitating short—term adaptation and long—term evolution. Not all the taxa in the southern United States could be given definitive names, as there are many taxonomic uncertainties. Quite a few of the taxa are obviously undescribed, and others are uncertainly equivalent to taxa from elsewhere bearing the same names. There is reason to believe that more north—south species pairs exist than the two already known.
On the Equivalence of Maximizing Reproductive Value and Maximizing Fitness
Authors: Caswell Hal
Published: May 2006

It is commonly accepted that a life history which maximizes mean fitness also maximizes the reproductive value of each age class. By deriving explicit formulae for the derivatives of fitness and of reproductive value, I show that this equivalence can hold only under a very special set of conditions relating survival and fecundity at different ages. These conditions are neither intuitively obvious nor supported by the data available at this time. This suggests that the applicability of theory based on reproductive value maximization may be limited.
Fruit Set, Herbivory, Fruit Reduction, and the Fruiting Strategy of Catalpa Speciosa (Bignoniaceae)
Authors: Stephenson Andrew G.
Published: May 2006

Catalpa speciosa regularly initiates more fruits than it matures. Most of the fruits that fail to mature are abscised from 2—5 wk after the flowering period. Catalpa speciosa has a host—specific herbivore, Ceratomia cactic (Sphingidae), which severely defoliates some branches while causing little or no damage to leaves of other branches. The pattern of fruit abscission was examined in relation to the principal herbivore. Field observations and experiments show: (1) the larger the infructescence, the higher the probability that a given fruit will abort; (2) branches that have experienced simulated herbivory have significantly more abortions than control branches;(3) if one fruit is aborted from an infructescence, the remaining fruits have a higher probability of maturing; (4) fruits accumulate <10% of their mature dry weight and total protein during the 1st 5 wk of growth and the remaining 90% in the next 4 wk (after the period of abortion). These data suggest that (1) each branch supplies the energy necessary to mature the fruits that it hears, (2) environmental stress, especially herbivory, reduces the resources available for fruit production, (3) fruit abortion is a response to limited resources, and (4) the pattern of fruit growth reduces the "cost" of abortion. The overall pattern of fruit reduction is interpreted as an adaptive trade—off between seed number and seed quality which permits the parent plant to match fruit production with available resources.
Trophic Basis of Production Among Net‐Spinning Caddisflies in a Southern Appalachian Stream
Authors: Benke Arthur C. , Wallace J. Bruce
Published: May 2006

Life histories and annual production were determined for six species of net—spinning caddisflies in a headwater stream of the Tallulah River in north Georgia, USA. Five species in the family Hydropsychidae were univoltine, whereas the sixth, a member of the Philopotamidae, had at least two generations per year. Combined annual production, as determined by the Hynes method, was 1.0 g/m2 (ash—free dry mass). Seventy—five percent of the production was concentrated in the two largest species, Arctopsyche irrorata and Parapsyche cardis. The remaining production from highest to lowest percent, was contributed by Dolophilodes distinctus, Hydropsyche sparna, Diplectrona modesta, and Hydropsyche macleodi. Analysis of gut contents alone indicated that detritus was the most important food source. However, food preference and food—specific ecological efficiencies were utilized to calculate the amount of production attributable to each major food category. Surprisingly, almost 80% of all caddisfly production was attributed to animal food, 13% to detritus, and 8% to algae. Actual annual consumption required to account for this production was 2.28 g/m2 animals, 2.54 g/m2 detritus, and 0.51 g/m2 algae. We attempt to quantify the role that net—spinning caddisflies play in the @`spiralling" of seston in mountain streams. Our results show that the omnivorous caddisflies are not the major consumer of detritus and algae, and that they produce more detritus in their feces than they consume, thus appearing to lower the food quality of the seston. Net—spinning caddisfly production in this mountain stream appears to be limited by the amount of high quality food available in the seston.
The Influence of Neighboring Hosts on Colonization of Prairie Milkweeds by a Seed‐Feeding Bug
Authors: Evans Edward W.
Published: May 2006

At Konza Prairie, Kansas, milkweeds (Asclepias viridis) were mapped and censused repeatedly to examine the influence of neighboring conspecifics on colonization of individual host plants by adults of the seed bug Lygaeus kalmii. Analysis by multiple regression suggests that the primary determinant of abundance of adult bugs on a host plant was the plant's own pod (seed) production; abundance of adult bugs also increased, however, with increasing pod production by adjacent plants. This neighborhood effect was limited to plants immediately adjacent to a host plant; pod density >3 m distant from hosts had little influence on colonization of hosts by bugs. Mark—recapture studies revealed differences in responses of the two sexes of L. kalmii to neighboring pod density: males lingered longer, while females lingered less on individual plants when these plants were surrounded by many vs. few pods. Damage from L. kalmii sustained by milkweeds thus results from a complex interplay of reproductive behaviors of individual host plants, their neighbors, and their seed predators.
Sex‐Related Foraging Behavior in Sequentially Hermaphroditic Hogfishes (Bodianus Spp.)
Authors: Hoffman Steven G.
Published: May 2006

I develop Schoener's proposal that the amount of activity time allocated to foraging can be sex related; males more often than females should minimize foraging time, and females should often be foraging—time maximizers. Sexual differences in foraging—time allocation may be small when male mating success is limited by available energy for maximizing sperm production. The foraging—time patterns of the sexes were examined in three sequentially hermaphroditic (protogynous) hogfishes in the genus Bodianus (Family Labridae). The daily social and mating activities of males in each of these marine reef fishes are distinctly different: single males defend permanent, all—purpose territories that contain a harem of females (B. rufus; San Blas Islands, Panama), males defend temporary reproductive territories (B. diplotaenia; Gulf of California, Mexico), or males are not territorial and spawn together in groups (B. eclancheri; Galapagos Archipelago, Ecuador). Female hogfishes in all three species mate daily and spend relatively little time on social and mating activities. Fertilization is external, and parental care of young is absent in these species. Time budget analyses indicated that B. rufus males allocated a much smaller proportion of their time (39.7%) to foraging than did conspecific females (76.8%). Protogyny in B. rufus provided a unique opportunity to test the effect of sex on an individual's time budget experimentally. Sex change by the dominant female was initiated in the field by removing the dominant, territorial male from his harem group. All (N = 9) individuals tested decreased the amount of time spent foraging and increased time allocated to social and mating activities, after they became reproductively functioning males. Sequential removals within harems indicated that the reduction in time spent foraging decreased with the number of female mates remaining in the group. Bodianus diplotaenia males also spent less time foraging (45.9%) than did conspecific females (76.5%). Bodianus eclancheri males spent most (70.2%) of their time foraging, as did conspecific females (77.3%). It appears that males minimize foraging time when their reproductive success depends more upon time spent in social and mating activities than upon net energy gains, as in B. rufus and B. diplotaenia. The reproductive success of female hogfishes, and males that compete for mates by maximizing sperm production (B. eclancheri), appears to be limited primarily by energy available for gamete production and growth; these individuals spend relatively little time engaged in social and mating activities and spend most of their time foraging.
Age, Sex, and Parasites: Spatial Heterogeneity in a Sandflat Population of Ilyanassa Obsoleta
Authors: Curtis Lawrence A. , Hurd L. E.
Published: May 2006

An intensive sampling study, undertaken in a natural sandflat population of an estuarine neogastropod, Ilyanassa obsoleta, revealed a marked degree of spatial heterogeneity for a number of important characteristics. Growth rate could be inferred by observing changes in size—classes over time, but the inequitable spatial distribution of size—classes renders size/frequency analysis impractical and of dubious predictive value for this population. Overall parasitism rate in this population is high, generally increases exponentially with increasing age, and creates a relatively narrow reproductive fenestra temporalis by apparently permanent sexual impairment of infected snails. In fact, the strong influence of parasites on behavior and physiology of snails may necessitate distinguishing between apparent and functional individuals, with regard to their role in estuarine benthic communities. However, incidence of both parasitism and parasite species is highly variable in space. Nearly half of all samples taken departed significantly from the overall sex ratio, indicating that distribution of sexes is also heterogeneous. Since there is little predictive relationship between specific samples and overall population trends, it is likely that differentiating between trends that are truly temporal and those that are in reality spatial is difficult at best. Moreover, high spatial heterogeneity in the field has implications for the interpretation of laboratory studies as well as those done in the field and indicates that generalizations about the biology and ecology of this species gleaned from small, albeit random, samples should be viewed with caution.
Annual Production of Macroinvertebrates in Three Streams of Different Water Quality
Authors: Krueger Charles C. , Waters Thomas F.
Published: May 2006

Macroinvertebrate annual production was estimated in three Minnesota streams that differed in watershed geologic origin and in total alkalinity. Annual mean alkalinities (as CaCO3) in the Caribou River, Blackhoof River, and North Branch Creek were 34, 83, and 245 mg/L, respectively. Annual production by herbivore—detritivore invertebrates was lowest in the Caribou River (wet mass: 27.0 g/m2), intermediate in the Blackhoof River (36.9 g/m2), and highest in North Branch Creek (119.6 g/m2). Estimates of annual production by invertebrate carnivores followed the same patter: lowest in the Caribou River (5.5 g/m2, intermediate in the Blackhoof River (6.5 g/m2), and highest in North Branch Creek (12.8 g/m2). These estimates of annual production were positively associated with alkalinity, nitrates, and fish standing stocks.
The Distribution of Evergreen and Deciduous Trees Relative to Soil Type: An Example from the Sierra Madre, Mexico, and a General Model
Authors: Goldberg Deborah E.
Published: May 2006

An example of the association of evergreen plants with nutrient—poor soils is described from the Sierra Occidental of northwestern Mexico. At elevations from 600 to 1100 m in this mountain range, distinct patches of evergreen—oak woodland are surrounded by subtropical deciduous forest in a mosaic pattern. To quantify the vegetation pattern and examine its environmental basis, vegetation and soil samples were taken throughout the elevational range of the mosaic. Analysis of the samples indicated that the patches of evergreen vegetation occur on extremely acid, infertile soils (derived from hydrothermally altered rock), while deciduous vegetation dominates on less acid, more fertile soil (derived from unaltered volcanic rock). The two community types have very little floristic overlap, and the deciduous forest has much higher density of woody plants and greater species richness. The actual location of boundaries between patches of the two community types can be more abrupt than can be accounted for by soil change. At higher elevations (above 1100 m) evergreen woodland is not restricted to acid soils and occurs on all soil types. These data are discussed in terms of a general model to account for the association of evergreen plants with nutrient—poor soils in the Sierra Madre as well as in other areas with similar growth form soil fertility patterns. I propose that evergreen plants would grow and survive at least as well on fertile soils as on infertile soils in isolation, but are unable to establish in dense, productive vegetation because of low growth rates associated with high carbon costs and low photosynthetic rates of evergreen leaves.
Genecology of Eastern Redbud (Cercis Canadensis)
Authors: Donselman Henry M. , Flint Harrison L.
Published: May 2006

Plants of eastern redbud (Cercis canadensis) from seed collected from native trees throughout the natural range show considerable morphological variation. Characteristics usually associated with xeric conditions, such as increased pubescence, thicker and smaller leaves, and efficient stomatal geometry, are correlated with evapotranspirational trends over the natural range, reaching extremes in western populations. Photoperiodic growth response, time of initiation of dormancy, rate and extent of acclimation, and chilling requirements of dormant buds also vary over the natural range. Plants of southern origin continue to grow under shorter photoperiods than northern plants, and are slower to enter dormancy under short days. Plants of northern origin acclimate more rapidly than southern plants. Degree of acclimation in a fixed time is correlated with climatic parameters as well as latitude and, in the case of first—stage acclimation, longitude as well as latitude. Chilling requirements for breaking bud dormancy increased with latitude, with Florida plants showing no dormancy or chilling requirement.
Competition Among Cladocera
Authors: Smith Daniel Wilkins , Cooper Scott D.
Published: May 2006

In situ enclosure experiments were used to asses the importance of competition to the population dynamics of three cladocerans (Daphnia pulex, Moina affinis, and Ceriodaphnia sp.) in a small pond. Competitive effects were nonlinear functions of cladoceran density, and both intra and interspecific competition were important determinants of the dynamics of the pond populations. The data suggested that the degree of competition was dependent on resource levels and the age of competitors. The major pond predator, Chaoborus, was able to control prey populations only when the densities of prey and phytoplankton were low.
How Abiotic Factors Affect the Distribution of Two Species of Tropical Predaceous Aquatic Bugs (Family: Naucoridae)
Authors: Stout R. Jean
Published: May 2006

Heavy runoff from watersheds affects lowland streams in two general ways. Either a stream experiences spates (increased forward velocity and scouring of stream bottoms) or it becomes inundated by water from larger rivers, causing the stream to be backflooded. This study shows how these features affect the abundances and distributions of two Costa Rican species of stream—inhabiting predaceous waterbugs, Limnocoris insularis Champion and Cryphocricos latus Usinger (Naucoridae). Backflooding in the Sura was found to have no subsequent effect on the abundances or distribution of either species. But in the Sabalo, which spates, nymphal populations of L. insularis significantly decrease after a spate because of loss of numbers and loss of previous habitat. During severe spates, adults of both species can be washed out, causing abundances to remain low for several months to periods > 1 yr. Abundances of nymphs and adults of C. latus are associated with fast current speeds, large rocks, and coarse—grained pebbles. These sorts of habitats are found in both streams. Even though C. latus is more common in the Sablo than is L. insularis, abundances of adults of the former species fluctuate more in the stream that spates than in the stream that does not, owing both to a high washout rate and to a slow recolonization rate. The basic pattern of distribution is explained by the difference between the flooding characteristics of the two streams.
Correlations Between Forest Layers in the Swan Valley, Montana
Authors: McCune Bruce , Antos Joseph A.
Published: May 2006

Compositional patterns of forest layers (tree, shrub, herb, bryoid, and epiphyte) are weakly correlated in the Swan Valley. While one can roughly predict the composition of one layer based upon the composition of another layer, different strata do not change composition across environmental gradients at the same rate or in the same pattern. The relative position of two or more stands in species space is different for different layers. Evidence in support of this conclusion was derived from: (1) correlation of dissimilarity matrices, (2) correlation of stand placement on ordination axes, and (3) comparison of stand groups defined by cluster analysis.
The Influence of Hydrologic Conditions and Successional State on Dissolved Organic Carbon Export from Forested Watersheds
Authors: Tate Cathy M. , Meyer Judy L.
Published: May 2006

Concentration and export of dissolved organic carbon (DOC) were compared in streams draining four southern Appalachian watersheds with different treatment histories in 1969—1970 and again in 1979—1980. In 1969—1970 the watersheds were: old field (1 yr old), hardwood coppice (7 yr old), white pine (13 yr old), and mature hardwood (undisturbed for at least 45 yr). DOC concentrations in 1969—1970 were three to four times greater than in 1979—1980 on all watersheds, and the differences among watersheds were consistent both years: old field > hardwood > pine > coppice. Concentrations were always greater during the growing season. Annual runoff was 50% greater in 1979—1980, and annual DOC export in 1979—1980 was half the 1969—1970 value in all watersheds. Annual export was greatest from the hardwood and old—field watersheds and least from pine and coppice watersheds during both years. Although there appears to be a trend toward decreasing DOC concentration and export over the first two decades of secondary succession, differences caused by periodic variations in runoff are far more significant than any successional changes observed.
Differential Colonization of Resistant and Susceptible Host Plants: Pemphigus and Populus
Authors: Moran Nancy A. , Whitham Thomas G.
Published: May 2006

Plants show extensive intrapopulational variation in quality as hosts for herbivores. Adaptive discrimination among individual host plants depends on the availability of plant traits that are present when plants are colonized and that are correlated with quality. Here, we examine the ability of colonizers to select appropriate hosts when colonization occurs long before feeding, and when traits available as cues may be least associated with host quality. In such systems the precision of host selection may be limited by a lack of appropriate cues at the time of colonization. In the life cycle of the aphid Pemphigus betae, autumn migrants select among host trees (Populus angustifolia and natural hybrids with P. fremontii) far in advance of the spring feeding stages, while trees are in a very different physiological condition. In order to estimate host quality, we censused successful and aborted galls on 34 trees in a Utah canyon during seven consecutive years, thus obtaining tree—specific rates of stem—mother survivorship. We estimated attractivity of these trees by censusing autumn migrants during 3 yr. Both survivorship and attractivity varied among trees, and differences among trees persisted across years. Tree—specific colonization rates were positively related to gall establishment. These results indicate that the actual colonization pattern is more adaptive than a random colonization process; however, the ability to select better hosts is far more perfect. To determine how migrants might use cues evident during colonization and correlated with quality, we examined the relationships between tree attributes in autumn and colonization rate and between these same attributes and stem—mother survivorship. One attribute, degree of leaf retention in autumn, was positively correlated with both colonization and subsequent progeny survival. Thus, the tendency to colonize trees retaining leaves longer in autumn may contribute to P. betae's limited ability to preferentially colonize better hosts. The results support the hypothesis that, in life cycles in which colonization and feeding are separated, the evolution of adaptive host discrimination may be constrained by the availability of appropriate cues.