bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow Regime, Juvenile Abundance, and the Assemblage Structure of Stream Fishes
Authors: Schlosser Isaac J.
Published: May 2006

The assemblage of fishes in a second—order stream in east—central Illinois was compared through seine sampling for two years with distinctly different flow regimes. In both years adult (age >0) fish were most abundant in late spring and early summer while juvenile (age 0) abundance peaked in late summer or autumn. Total density of adult fish differed little between years but large changes in juvenile abundance occurred between years in association with differences in hydrologic regime. High stream discharge had little influence on abundance of juvenile suckers and darters, but some minnow species and all sunfish species exhibited large increases in juvenile abundance during stable to low flow conditions. The largest increase in juvenile abundance occurred among species with prolonged breeding seasons: bluntnose minnow (Pimephales notatus) and striped shiner (Notropis chrysocephalus). Increased juvenile abundance during stable flow conditions resulted in increased species richness in small habitat patches and annual changes in species composition of the community. Models of fish assemblages in small streams need to incorporate ontogenetic changes in the role of stochastic environmental variables in regulating the population size of component species.
Behavior and Ecological Interactions of Larval Odonata
Authors: Pierce Clay L. , Crowley Philip H. , Johnson Dan M.
Published: May 2006

Enallagma aspersum and E. traviatum (Odonata: Coenagrionidae) are the most abundant larval odonates in Bays Mountain Park (Sullivan County, Tennessee, USA), although their spatial distributions are essentially nonoverlapping. E. traviatum coexists with insectivorous fish in a small lake, whereas E. aspersum is restricted to a small fishless pond nearby. Behavioral observations revealed that E. aspersum larvae were more active than E. traviatum, and tended to occupy more conspicuous positions. E. aspersum also enganged in more confrontations than E. traviatum, especially at higher density. In laboratory experiments with juvenile bluegills (Lepomis macrochirus) as predators, E. aspersum larvae were more vulnerable to predation than E. traviatum. Red—spotted newts (Notophthalmus viridescens) also preyed on E. aspersum disproportionately. Field enclosure experiments revealed that dry mass of individual E. aspersum larvae was density dependent, and that increased density of E. aspersum or addition of E. traviatum produced similar reductions. Competition was asymmetrical, as E. aspersum appeared to have no significant effect on E. traviatum. The substantial increase in confrontations among E. aspersum larvae at higher density, and the lack of evidence for prey depletion, suggest that interference may be the mechanism of competition. Our results suggest that the distribution of E. aspersum larvae may be limited by fish predation, but although competitive interactions were detected, we have no evidence that larval competition influences the distribution of either species.
Joint Effects of Competitors and Herbivores on Growth and Reproduction in Aristolochia reticulata
Authors: Fowler Norma L. , Rausher Mark D.
Published: May 2006

The separate and joint effects of herbivory and interspecific competition on an herbaceous plant were measured to determine to what extent, if any, herbivory and competition interact in their effects, and to test models of their joint effects. Plants of Texas Dutchman's pipevine, Aristolochia reticulata, were grown in a greenhouse, alone and in competition with either or both little bluestem grass, Schizachyrium scoparium, and southern dewberry, Rubus trivialis. Herbivory on A. reticulata by the pipevine swallowtail butterfly, Battus philenor, and on S. scoparium by cattle was simulated by clipping. Competition and clipping individually had the expected negative effects on A. reticulata growth and reproduction. The joint effect of competition and clipping on A. reticulata was best described as additive. The joint effect of the two competing species on A. reticulata in three—species mixtures was well predicted by a simple, but nonlinear, model that assumed that all three species competed for the same limiting resource. The results of this study suggest that the structure and dynamics of this community, and by extension those of other communities, can be understood by examining subsets of the community separately.
The Influence of Recruitment, Competition, and Benthic Predation on Spatial Distributions of Three Species of Kelp Forest Gastropods (Trochidae: Tegula)
Authors: Watanabe James M.
Published: May 2006

Factors influencing the bathymetric segregation of three species of turban snails (Tegula) were examined in Monterey Bay, California. Two of the three species are abundant: Tegula brunnea occurs in shallow water (0—6 m), and T. pulligo occurs in deep water (7—12 m). Tegula montereyi occurs at intermediate and deep depths but is relatively rare. I examined the effects of larval recruitment, interspecific competition, and benthic predation on the maintenance of these patterns. The distribution of recently settled juvenile snails coincides closely with adult distribution, indicating that planktonic larvae of the three species may settle differentially to different depths. Juveniles of the two abundant species occur in different microhabitats at the extremes of their adult ranges: juvenile Tegula brunnea occur in the low—intertidal/shallow—subtidal zone on algae—covered rock substrate, and juvenile T. pulligo occur in deep water (11—12 m) on shell—fragment rubble. T. montereyi juveniles are less abundant than those of the other two species, depth and microhabitat distributions are similar to those of T. pulligo. Competition among the three species is not strong; neither food nor space limitation appears to occur in nature. The effects of competition on patterns of movement and habitat use in the field and on growth and reproductive development in the laboratory showed that interspecific and intraspecific effects were not significantly different. In addition, densities at which competition would have a strong effect are probably much higher than those that occur naturally. It is unlikely that competition is responsible for the bathymetric segregation of the three species. The major predators of Tegula are benthic invertebrates and demersal fishes. Tegula have two spatial refuges predators: kelp plants (which allow snails to stay off the primary substratum and away from predators) and dense benthic vegetation (predators cannot detect and capture snails as easily in areas of dense vegetation). Benthic predation pressure increases with increasing substrate depth because (1) the cover of protective benthic vegetation decreases significantly, and (2) predators are more abundant in deeper water. Higher predation pressure in deeper water limits adult Tegula brunnea to shallower depths. Individual T. brunnea spend more time on the kelp forest floor than do individuals of the other two species causing them to be killed at a disproportionately higher rate in deeper water. Benthic predation is also responsible for the concentration of T. pulligo on kelp plants in deeper depths, but cannot explain why this species is not more abundant in shallow depths. The rarity of T. montereyi is not caused by predation, since this species is the best defended of the three against starfish. For both species, patterns and intensities of larval settlement may be of primary importance. Further information on the larval biology of these species is needed.
Leafminers, Early Leaf Abscission, and Parasitoids: A Tritrophic Interaction
Authors: Kahn D. M. , Cornell H. V.
Published: May 2006

We investigated the interplay of the native holly leafminer, Phytomyza ilicicola, and leaf abscission by the American holly, Ilex opaca, an evergreen understory tree which is extensively planted as an ornamental. We carried out our study at both an urban and a forest site in northern Delaware. Leaf abscission rates increased in response to mining by Phytomyza. However, early abscission either did not affect or increased miner survivorship. This result differs from several previous studies in which leaf abscission has been found to decreased herbivore survivorship. One reason for lack of a negative effect was that leaves were not dropped until miners had pupated in the leaf. The other reason is reduced parasitism; since parasitoids did not search fallen leaves, abscission actually decreased mortality due to these natural enemies. Overall, our results indicate that the timing of leaf abscission in relation to the life cycle of herbivorous insects, and in relation to natural enemy attack, will determine how abscission influences herbivore demography.
Role of Uprooting in Composition and Dynamics of an Old‐growth Forest in Japan
Authors: Nakashizuka Tohru
Published: May 2006

Seedling, sapling, and tree composition in several types of gap and nongap microsites were examined in an old—growth temperate mixed forest in western Japan. The distribution of species was not related to gap size (10—340 m2). Seedling communities on tip—up mounds and those on fallen boles of coniferous trees were rich and composed of pioneer species. In contrast, understory composition in gaps without uprooting did not differ from undisturbed forest. Dwarf bamboo, which dominates the forest floor and prevents tree regeneration, magnifies the effect of uprooting. Species with small, wind—dispersed seeds were found mainly on disturbed soil, while species with large, animal—dispersed seeds did not have any bias in distribution. Soil disturbance is a more important feature of the disturbance regime of this forest than is gap formation, with regards to maintaining species richness.
Complete Estimates of Repreductive Success in a Closed Population of Smallmouth Bass (Micropterus Dolomieui)
Authors: Raffetto Nancy S. , Baylis Jeffrey R. , Serns Steven L.
Published: May 2006

We conducted a 4—yr study of 154 parental male smallmouth bass (Micropterus dolemieui) and 982 nests in a closed natural population (a temperate seepage lake in Wisconsin). Our goal was to test common assumptions and hypothesis about reproduction in natural populations. Mark—recapture techniques were used to measure changes in the demography, age—specific sex ratios, and mortality rates of the whole population. An area—density method was used to estimate the number of eggs spawned in each sampled males's nest, and we volumetrically estimated the number of larvae produced by sampled males. The lake is closed to migration, allowing us to accurately estimate total population size and individual variance in reproductive success (RS) for each year without having to assume a demographically stable population. We found that a large proportion of non—breeding adults of both sexes were present in each year. We compared estimates of variance in RS among subsets of males and females in the population to examine the effect on variance when mature non—breeding individuals are included in the analysis. Excluding non—breeders resulted in the true variation in RS being underestimated and the mean RS overestimated, both by a factor of °3 for males and 2 for females. Most male bass spawned only once in their lifetimes, and size at age 3 yr appeared to determine whether a male spawned or postponed reproduction. Males that bred at age 3 yr were among the largest of their cohorts, and males that bred at age 5 yr were among the slowest growing. There may be greater selection on adults for opportunity to breed than there is selection in RS among breeding adults in this population.
Interactive Effects of Predators and Early Larval Dynamics of the Treefrog Hyla Chrysocelis
Authors: Fauth John E.
Published: May 2006

Ecologists need to determine the frequency and nature of higher order interactions and to predict when such interactions will be important to understand community dynamics. I experimentally tested for higher order interactions in a freshwater food web by independently manipulating the presence and absence of two predators (the salamander Notophthalmus viridescens and the crayfish Cambarus bartonii) and their tadpole prey (Hyla chrysoscelis) in a series of artificial ponds. By destructively sampling selected ponds early in the larval period (days 5 and 6), I hoped to predict whether the predators would have an interactive effect on tadpole survival and growth on day 30. Early destructive samples adequately predicted subsequent influences of interactions on the survival, but not on the size of Hyla. Early samples predicted that the predators would interact to determine tadpole survival and size. The two predators did not act additively to determine tadpole abundance: more survived in the presence of both predators than was predicted. This higher order interaction was most likely caused by physical interference between the predators and predator avoidance by the tadpoles. Early samples correctly predicted higher order interactions would be seen on tadpole growth, but completely failed to predict their direction because the biological interactions changed over time. Early in their larval period, tadpoles behaviorally avoided predators, which caused slower growth, but later, tadpoles in predator treatments grew faster due to diminished intraspecific competition. These results suggest that higher order interactions may be important in nature. Short—term experiments may prove useful in predicting when higher order interactions will occur, but detailed models may be required to predict their outcome accurately.
Collapse of an Ant‐Plant Mutalism: The Argentine Ant (Iridomyrmex Humilis) and Myrmecochorous Proteaceae
Authors: Bond W. , Slingsby P.
Published: May 2006

Many plant species in Cape fynbos shrublands have seeds dispersed by ants. Iridomyrmex humilis, the Argentine ant, has recently invaded areas of fynbos and displaced the dominant native ants. The consequences of the invasion for seed dispersal were studied. Iridomyrmex differed from native ants in being slower to discover the seeds (morphologically achenes) of ant—dispersed Mimete cucullatus (Proteaceae), in moving them shorter distances, and in failing to store them in nests elow the soil. Seeds left on the soil surface were eaten by vertebrate and invertebrate predators. To study seedling emergence, seed depots were established and then the area was burned. Emergence was 35.3% in sites not infested by Iridomyrmex and 0.7% in infested sites. Seedlings in naturally occurring stands of M. cucullatus burnt in the same fire were widely distributed in noninfested sites, but were fewer and were confined within the canopy radius in infested sites. We suggest that continued invasion of fynbos by Iridomyrmex may eventually lead to extinction of many rare, endemic Cape Proteaceae by slow and subtle attrition of seed reserves.
Competition in Natural Populations of Mycophagous Drosophila
Authors: Grimaldi David , Jaenike John
Published: May 2006

In the northeastern United State, individual mushrooms commonly harbor the larvae of up to four species of Drosophila (D. Falleni, D. Recens, d. putrida, and D. Testacea), as well as larvae of crane flies (Tipulidae), wood gnats (Anisopodidae), and other, small flies. An experiment showed that larvae of these species commonly exhaust the food in single mushrooms under natural conditions. Supplemental mushroom increased survival to adulthood in three drosophila species and resulted in larger adult flies. There was substantial variation among individual mushrooms in the degree of food depletion by larvae; while some mushrooms were completely devoured, others appeared to provide more than enough food for the larvae. Mean body size of Drosophila that matured in nature were similar to those of flies reared in our experiments without supplemental food, which suggests that resource depletion and larval competition are common in natural populations of these species. (While the evidence for resource limitation is compelling, our methods do not allow us to distinguish between intra— and interspecific competition.) As a result, fitness of flies in nature should vary greatly as a function of the amount of food available to larvae. We speculate that low rates of parasitism allow mycophagous drosophila populations to deplete food resources more commonly than do phytophagous insects.
Intraspecific Competition in the Tephritid Fruit Fly Rhagoletis Pomonella
Authors: Averill Anne L. , Prokopy Ronald J.
Published: May 2006

At densities found in nature, competition among larvae of the frugivorous fruit fly Rhagoletis pomonella (Diptera: Tephritidae) was pronounced. In fruits of Crataegus mollis, a small native host of the fly, survivorship dropped sharply when >1 larva developed per fruit. Multiple infestation also caused decreased size of pupae, which resulted in prolong maturation of females and lower daily fecundity. Our findings suggest that interference competition occurs among rival R. pomonella larvae within the same fruit and that older larvae may be competitively dominant. In most instances, when 2 d separated the introduction of two larvae into unpicked fruits of Crataegus oxyacantha, a very small ornamental hawthorn, the first larva pupated while the subsequent larva failed to complete development. Rhagoletis pomonella marks its oviposition site with a contact pheromone. The amount of pheromone deposited following a single egg—laying in C. mollis fruit was sufficient to deter most females from laying more eggs. By avoiding marked fruits in which a larva is already developing, a female may conserve eggs and add measurably to her fitness. Because most C. mollis fruits can support more larvae to puparium formation than they actually do, it appears that the strategy of host marking by females and monopolization of fruit by larvae may leave some fruit resources unexploited.
Longleaf Pine Pyrogenicity and Turkey Oak Mortality in Florida Xeric Sandhills
Authors: Rebertus Alan J. , Williamson G. Bruce , Moser E. Barry
Published: May 2006

Logistic multiple regression models were constructed for turkey oak crown survival and resprouting in two experimental fires. Crown survival patterns were similar in the mild and the more intense fire. Crown survival was positively related to "turkey oak diameter at breast height (dbh)," and "distance to the nearest large longleaf pine"; it was inversely related to the "dbh of the nearest pine." The crowns of small turkey oaks (2.5—5.5 cm dbh) rarely survived the intense fires fueled by needle litter in the vicinity of longleaf pines, while large turkey ocaks (>10 cm dbh) had high crown survival regardless of location. In the mild fire, pines affected the survival of small turkey oaks within a distance of at least 10 m, while in the hotter fire pines appeared to affect the survival of small turkey oaks within at least 25 m. In the mild fire, 68% of the crown—killed oaks resprouted, and the probability of resprouting was inversely related to both "turkey oak dbh," and "distance to the nearest pine." Most trees that failed to resprout had delayed crown mortality. In the hotter fire, 95% of crown—killed oaks resprouted, and resprouting was inversely related to "turkey oak dbh." Although the pyrogenicity of longleaf pine also leads to segregation of adult pines and their seedlings, most oaks are adversely affected by fires within the zone of maximum pine seedling recruitment. Thus, reduced competition from oaks may increase the fitness of longleaf pines and favor selection for pyrogenicity.
Does Invasion Sequence Affect Community Structure?
Authors: Robinson James F. , Dickerson Jaime E.
Published: May 2006

The effects of invasion sequence on community structure were evaluated using aquatic microcosms. Thirty 400—mL beakers were inoculated with replicated subsets of species from a species pool consisting of green, blue—green, and golden algae, ciliates, a rotifer, a dinoflagellate, and euglenoids. These species were added according to four distinct sequences and two different rates over a 23—wk period, resulting in four replicated sets of insular communities. Significant differences in community structure and species richness could be attributed to both sequence of invasion and distance effects. "Priority" effects were found to be important in some but not all instances. Communities could be divided into two primary types that are similar to the two community types previously reported to arise from the assembly of these same taxa according to different invasions schedules.
Density‐Dependent Paedomorphosis in the Salamander Notophthalmus Viridescens Dorsalis
Authors: Harris Reid N.
Published: May 2006

The newt Notophthalmus viridescens has long been noted for its variable life history. In this experimental study, larval density was a significant determinant of this variation. Low larval density was associated with rapid larval growth, paedomorphosis, and sexual maturity. A fourfold increase in density was associated with slower growth and metamorphosis into the sexually immature eft form. A similar result was obtained when the experiment was repeated. The evolutionary hypothesis that paedomorphosis results when aquatic growth conditions favor rapid growth was supported. The observed paedomorphosis could not be attributed with certainty to the effects of progenesis or neoteny, since the normal metamorphic form was dimorphic in timing the first reproduction.
Life Cycle Characteristics of Aster Pilosus in Early Succesional Habitats
Authors: Peterson D. L. , Bazzaz F. A.
Published: May 2006

Aster pilosus is a perennial common in early successional fields. In much of the eastern United States, it becomes prominent in 2nd—yr and 3rd—yr old—fields. Its survivorship, growth and flowering are influenced greatly by competition with summer annuals. Spring—germinated individuals are flexible with respect to age of 1st reproduction; they flower during the fall or delay flowering for a year under resource— and especially nutrient—limiting conditions. Fall—germinated plants form rosettes that overwinter and bolt the following spring. Most Aster individuals are iteroiparous and remain established in the field for several years. Flowering, which is dependent on size rather than age, is apparently controlled photoperiodically only after a threshold of growth has been attained. Bolted individuals which are 2 yr old have a much higher seed output than reproducing plants in 1st—yr communities, although reproductive effort is the same. Germination is most favorable under high levels of irradiance, red light, and moderately high concentrations of NO2—, conditions associated with disturbance. Photosynthetic response changes ontogenetically, and productivity is maximized under changing light conditions of the developing plant community. High rates of photosynthesis under water limitation and over a broad range of temperature indicate the tolerance of Aster to the variable environmental conditions of early successional habitats. Aster is an early midsuccessional plant that keys is on disturbance. It does not compete well with 1st—yr annuals in growth from seed. However, the perennial habitat provides it with a competitive advantage over the annuals in subsequent years. Although early reproduction may be sacrificed by Aster under resource—limited conditions, investment of energy in overwintering rosettes guarantees continued establishment in the site and future opportunities for reproduction by seed.
Differential Predation on Metamorphic Anurans by Garter Snakes (Thamnophis): Social Behavior as a Possible Defense
Authors: Arnold Stevan J. , Wassersug Richard J.
Published: May 2006

The diets of garter snakes (Thamnophis) collected at several localities were examined and the developmental stage of anurans in the diets were recorded. During periods of anuran metamorphosis, garter snakes converge on the shoreline and their diets are biased towards transforming stages. This bias appears to reflect the locomotor ineptitude of metamophosing anurans;a transforming anurans can neither swim nor hop as effectively as premetamorphic tadpoles or postmetamorphic frogs, respectively. Metamorphic synchrony in certain anurans (e.g., Bufo) may have evolved as a defense against predation during metamorphosis. This synchrony could satiate predators. Certain anurans (e.g., Bufo, Scaphiophus) form postmetamorphic aggregations which may represent `selfish herds' in which individuals gain protection by association with more vulnerable conspecifics.
Dispersal and Population Variation in the Bryozoan Bugula Neritina
Authors: Keough Micheal J. , Chernoff Helen
Published: May 2006

The scale of spatial and temporal fluctuations is described for populations of the arborescent bryozoan Bugula neritina, and observational and experimental data were used to explain these fluctuations. Colonies were found to be abundant on seagrasses in the northern Gulf of Mexico from mid to late fall through winter. Populations increase in mid to late fall, roughly with the onset of cooler weather. They decline between midwinter and early summer, apparently when cold fronts pass. We found no colonies on seagrass in summer, but some large colonies attached to polychaete tubes lie dormant through summer, regenerating in fall. Spatial variation occurs on very small scales. Bugula were absent from some seagrass patches, even when substantial populations were <100 m away. Sites with Bugula populations in one season had populations in subsequent seasons, while seagrass patches without Bugula lacked Bugula at other times. This suggests that there is little interaction between spatial and temporal variation. The absence of Bugula neritina from patches of seagrass is not the result of poor survival of post—settlement individuals, but rather is likely due to poor dispersal of the lecithotropic larvae. Newly metamorphosed juveniles were transplanted to sites with (university marine lab) and without (Lanark) natural Bugula populations. Mortality was uniformly high (°70%) for the 1st wk after settlement, but in the 2nd wk transplanted juveniles had higher survivorship at the Lanark site. In weeks 3 and 4 there were no significant differences and °80% survival at both sites. For weeks 4—8, mean survivorship decreased to 50%/wk at the marine lab site, while remaining >80% at Lanark. Growth rates were also higher at the site without natural Bugula colonies, and colonies there began to reproduce 1 wk sooner than those at the marine lab site. Juveniles transplanted to Lanark reproduced, and their offspring grew and reproduced successfully, producing a second generation of Bugula. The newly established population persisted through summer and was still present in 1986. Local extinctions of Bugula populations are probably caused by storms; one such extinction was observed. The spatial pattern is maintained by restricted dispersal and population bottlenecks. Unoccupied seagrass patches are unlikely to be colonized by larvae, but rafting of mature colonies on seagrass occurs frequently, with the potential of seeding new habitats.
The Role of Fine Roots in the Organic Matter and Nitrogen Budgets of Two Forested Ecosystems
Authors: McClaugherty Charles A. , Aber John D. , Melillo Jerry M.
Published: May 2006

Standing crop, rates of production, mortality, decomposition, and nitrogen dynamics of two size classes of fine roots (0—05 mm and 0.5—3.0 mm diameter) were estimated for 1 yr in a 53—yr—old red pine (Pinus resinosa Ait.) plantation and in an adjacent 80—yr—old mixed hardwood stand in north—central Massachusetts. Dry matter of live fine roots was higher in the hardwoods (mean = 6.1 Mg/ha; annual range 3.6—8.6 Mg/ha) than in the plantation (mean = 5.1 Mg/ha; annual range 2.5—7.8 Mg/ha.) Dead root mass was similar in the hardwoods (mean = 4.4 Mg/ha) and the plantation (mean = 4.0 Mg/ha). Nitrogen standing crop of live roots in the hardwoods was higher than in the plantation (mean = 65 kg/ha and 42 kg/ha, respectively). Net fine root production was estimated from changes in standing crop. Production estimates ranged from 4.1 to 11.4 Mg°ha—1°yr—1 in the hardwoods and from 3.2 to 10.9 Mg°ha—1°yr—1 in the plantation, depending on the assumptions made in the calculations. Concurrent estimates of total nitrogen requirement for this production ranged from 73 to 184 kg°ha—1°yr—1 in the hardwoods and from 44 to 122 kg°ha—1°yr—1 in the plantation. Decomposition, measured as mass loss from buried cloth bags, was °20% in 0.4—mm mesh bags and as high as 47% in 3—mm mesh bags after 1 yr. Integrating production and nitrogen requirements with estimates of decomposition rates and nitrogen mineralization for these ecosystems suggested that the lower estimates of production are more accurate.
Role of Body Temperature in the Seasonality of Daily Activity in Tenebrionid Beetles of Eastern Washington
Authors: Kenagy G. J. , Stevenson R. D.
Published: May 2006

On four occasions between spring and fall we studied populations of eight species of tenebrionid beetles in the arid Artemisia steppe of eastern Washington, USA. We obtained simultaneous but independent measures of (1) the times at which beetles were active, (2) body temperature (Tb) of beetles active on the surface, and (3) meteorological parameters (temperatures, radiation, wind seed). Ninety—seven percent of the 255 Tb's obtained between April and October ranged between 10° and 30°C (mean = 20°), and we observed no systematic seasonal shift Tb of active beetles. In contrast, environmental temperature was strongly seasonal, and in order for beetles to be active within the same 10°—30° range of Tb at all seasons, their activity patterns were not to the same phase of the daily light—dark cycle at all seasons. Rather, the beetles were strongly day—active in early spring and fall, mostly active during twilight and at night in the midst of summers, and active bimodally (morning and evening)in between these seasons. Tb's predicted with a biophysical model using our meteorological data correlate significantly with actually measured Tb's (r2 = .70) and can be used to predict satisfactorily the times of day when beetles are active. Some direct measures of environmental temperatures predict Tb more accurately than the model. Advantages of biophysical modelling are discussed. The tenebrionid beetles we studied have a range of Tb's during activity which is 10°—15° lower than that of many other terrestrial insects, including other insects in the same habitat and other species of tenebrionids found in more extreme desert environments. We suggest that tenebrionids in the eastern Washington steppe have evolved a low range of active Tb's as part of a strategy by which the season of activity is expanded into earlier and later times of year, when both quantity and quality of food may be greater.
Architecture, Light Interception, and Distribution of Larrea Species in the Monte Desert, Argentina
Authors: Ezcurra Exequiel , Montana Carlos , Arizaga Santiago
Published: May 2006

This paper analyzes the correlation between leaf orientation and the environmental conditions that prevail within the biogeographic range of each of the four South American Larrea species (L. ameghinoi, L. cuneifolia, L. divaricata, and L. nitida; Zygophyllaceae). Data on the distribution of Larrea species were gathered from herbarium specimens. Measurements of leaf orientation were made throughout the Monte Desert, and in more detail in northern Patagonia, where the four species coexist. The direct solar radiation intercepted by the unshaded leaves of each species was estimated through a computer model and plotted as a function of the hourly time for the summer and winter solstices. L. ameghinoi presents horizontal leaves and prostrate growth, characters which allow its development on sites that are exposed to the Patagonian westerlies. The species, however, is an inefficient light interceptor in winter and early spring, when moisture conditions are adequate in Patagonia. Its architecture is the result of selection for cushion—type, wind resistant forms, at the expense of light interception. It is restricted to windy, open areas of the Patagonian steppe. L. cuneifolia shows erect, east—facing leaves and branches, which maximize interception in the early morning and late afternoon, keeping noon interception at a minimum. It can tolerate very hot environments by physically evading the midday sun and intercepting more early morning and late afternoon light. It colonizes the hotter and drier parts of the Monte Desert. L. divaricata has divaricate leaves with folioles uniformly distributed in all azimuthal directions, and showing an inclination of around 70°. Although it never shows maximum light interception efficiencies, it preforms relatively well in all seasons and at all hours of the day. Its distribution is wide, not only in the arid Monte, but reaching also the Chaco woodlands and the Pacific coastal deserts. L. nitida shows erect, north—facing leaves and branches. Its leaf orientation distribution allows the gradual warming of the leaf surfaces during the morning, with a maximum light interception near winter noons. The species grow in the Patagonian Monte and on the slopes of the Andes. Its general affinity with the colder west side of the Patagonian and Monte Deserts links its distribution with winter—type rains of Pacific origin. The results suggest that the contrasting leaf orientations of the four South American Larrea species reflect the prevalent selective conditions endured under long periods in isolation, and that leaf orientation is an adaptive character that influences the habitat specificity of the different species.
Nesting Behavior and the Evolution of Worker Tempo in Four Honey Bee Species
Authors: Dyer Fred C. , Seeley Thomas D.
Published: May 2006

Three Asian honey bee species (Apis florea, A. cerana, and A. dorsata) were studied in Thailand, and compared with the European honey bee A. mellifera, to explore the energy implications of interspecific differences in worker body size and nesting behavior. From previous work on these four species, we know that several measures of the energy—related performance of foragers (body temperature, flight speed, wing loading, and mass—specific metabolic rate) deviate from predicted size—dependent patterns. Instead, workers in the two species intermediate in body size, A. cerana and A. mellifera, appear to be high—powered relative to those of the largest species (A. dorsata) and the smallest species (A. florea). Among the Asian species, A. cerana's colonies also show a disproportionately high mass—specific metabolic rate, and their foragers make many more trips per day in the same habitat than do foragers of the other species. These various traits seem to be functionally related, and to represent evolved differences among species in worker "tempo," i.e., in the rate of performance of colony tasks. Correlated with the dichotomy in worker tempo is a dichotomy in nest architecture and intracolony demography. The low—tempo species (Apis florea and A. dorsata) nest in the open, protecting the comb and its contents with a thick curtain of young worker bees. The high—tempo species build their nests in enclosed cavities, which allows the workers to protect and provision a relatively larger area of comb. Worker life—span is longer in the open—nesting species; this allows colonies to maintain the work force needed for the curtain, even though the rate of worker production (per capita) is lower than that of cavity nesters because of the relatively small number of brood cells available. With the assumption that there is a fundamental relationship across species among tempo, foraging performance, and the rate of mortality, we propose that the relatively high tempo of cavity—nesting workers has been favored for two reasons. First, a benefit of higher tempo (enhanced ability to provision brood) is better realized owing to the greater brood—rearing capacity of their nests. Second, a cost of higher tempo (shorter life—span, resulting in fewer workers available for nest production) is less important for the cavity nesters because the cavity walls reduce the need for protection by workers.
The Effects of Substrate Texture, Grazing, and Disturbance on Macroalgal Establishment in Streams
Authors: Dudley Tom L. , D'Antonio Carla M.
Published: May 2006

Two common macroalgae, Cladophora glomerata (a filamentous chlorophyte) and Nostoc parmeloides (a colonial cyanobacterium), are strongly associated with rough substrates in Rattlesnake Creek, a second—order stream in coastal Santa Barbara County, California. To test the hypothesis that rough texture reduces algal mortality from invertebrate grazers and from winter storms, we conducted a series of experiments on two substrate types (titles) that varied only in surface heterogeneity. The dominant grazer, the caddisfly Agapetus celatus, was excluded from tiles using petroleum jelly barriers, and algal establishment was compared with that on control tiles; grazing experments were repeated during spring and autumn. In a separate experiment, storm scouring was simulated by manually scrubbing naturally colonized rough and smooth tiles at different intervals (7 wk, 3 wk, and once, with an undisturbed control) from December to June, during which algal establishment and survival were monitored. In the absence of Agapetus, Cladophora was found nearly equally on rough and smooth surfaces. Grazers strongly reduced Cladophora establishment on all surfaces (often by >80%); texture did not generally influence grazing effects in autumn, but refuges (pits) greatly increased algal survival in spring when recruitment was greater. Two other grazing insects (Baetis spp. and Micrasema) increased on exclusion tiles, apparently due to competitive release, but did not eliminate effects of Agapetus. Manual disturbance at 3— and 7—wk intervals kept Cladophora densities much lower than on control and once—scoured tiles. Densities were higher on rough tiles, but the interaction between disturbance and texture was not significant for macroalgae; however, microscopic examination showed that basal filaments, and new sporelings, were protected within depressions. Nostoc attained densities in autumn of °50—100 colonies/100 cm2 on rough tiles and was virtually absent from smooth tiles. Unlike Cladophora, Nostoc was little affected by grazing, but was greatly reduced by disturbance. Rough texture provided minor protection, but mature Nostoc formed basal crusts that resisted disturbance, thereby maintaining space in the absence of severe scour. Substrate heterogeneity provides refuges from herbivory and disturbance for establishing macroalgae. While it increasingly appears that herbivory plays a profound role in determining algal dynamics in streams, herbivores and substrate texture may also interact to modify the rate and direction of benthic succession. By inhibiting the establishment of intermediate taxa (e.g., Cladophora), grazers may restrict succession on smooth substrates to an early, diatom—dominated assemblage, or accelerate dominance by later taxa (e.g., Nostoc) on rugose substrates.
A Gradient Analysis of Southern Wisconsin Forests
Authors: Peet Robert K. , Loucks Orie L.
Published: May 2006

While study of southern Wisconsin forests has led to numerous conceptual advances in ecology, a clear understanding of variation in these factors in relation to environmental factors and successional processes has failed to emerge. The present study was undertaken to (1) determine the principal factors controlling or closely correlated with forest composition, (2) formulate a multidimensional gradient representation using these factors, and (3) reexamine forest composition and dynamics using this representation. It was also expected that this study might help place in perspective the extensive early research on Wisconsin forests and subsequent methodological advances in gradient analysis and ordination. Principal component analysis was used to represent compositional variation of southern Wisconsin forests. Analysis of environmental variation within the resultant ordination suggested two gradients to account for much of the variation observed. These were a moisture—nutrients gradient based on soil texture and a dynamics gradient based on tree size—class data. These gradients, reformulated, serve as axes in a two dimensional scheme of forest characterization. Within this characterization scheme, early successional forests on mesic to xeric sites respectively are dominated. by Quercus rubra, Quercus alba, Quercus macrocarpa, and Quercus velutina. On mesic sites succession proceeds through stands dominated by Ulmus rubra to dominance by Acer Saccharum. Dry—mesic stands appear to have dominance shared at climax by Q. alba, Carya ovata, and Prunus serotina. On extreme xeric sites. Q. macrocarpa and Q. velutina tend to form stable stands. Thus, the successional sequence becomes progressively shorter toward the xeric end of the moisture—nutrient gradient. The original continuum of Curtis and McIntosh was an abstract gradient implying no direct relationship to either site condition or successional status. Use of such factors in the present characterization allows a more precise conceptualization of functional relationships between forest types. In addition the methodology illustrates the complementary usage of mathematical ordination as an exploratory tool and gradient analysis as both a means of representing the relationships discovered and as a framework within which additional critical questions can be formulated and addressed.
Influence of Sunlight on Photosynthesis, Water Relations, and Leaf Structure in the Understory Species Arnica Cordifolia
Authors: Young Donald R. , Smith William K.
Published: May 2006

Intraspecific variation in photosynthesis, transpiration, and leaf structure according to natural exposure to sunlight was evaluated for the understory species Arnica cordifolia (Compositae) within the Rocky Mountains of southeastern Wyoming. Plants were arbitrarily divided into sun plants (receiving >12.6 MJ°m—2°d—1) and shade plants (receiving <4.2 MJ°m—2°d—1). Significant differences in sunlight patterns and windspeeds at locations with sun or shade plants led to variations in leaf temperature, stomatal resistance, xylem water potentials, and photosynthesis. Very small differences in soil water potentials and air temperatures occurred between sun and shade plant locations. Leaf size, thickness, and trichome density along with chlorophyll contents also varied between leaves from sun and shade plants. Sunlit periods for sun plants contained nearly twice as much energy and quantum flux and lasted nearly twice as long as sunlit periods for shade plants. Windspeeds and soil temperatures were also considerably greater at sun plant locations. Stomatal opening occurred for both sun and shade plants during sunlit periods which led to large increases in pohotosynthesis and transpiration. Aerodynamic leaf resistances accounted for >50% of the total leaf resistance to water loss for plants in full sun, while the mesophyll resistance accounted for >80% of the total leaf resistance to CO2 uptake for both sunlit and shaded plants. Sun plants had higher photosynthetic rates, light saturation values, and temperature optima for photosynthesis. Leaves of sun plants also had large stomata, almost twice as many trichomes, and were °1.3 times as thick as leaves from shade plants. Chlorophyll contents were 36% greater in shade plants when expressed as a mass per mass basis, but 47% less if expressed as mass per leaf area. The results are discussed in terms of adaptive mechanisms for the evolution of sun— or shade—tolerant species in understory habitats.
Dynamics of a Black‐capped Chickadee Population, 1958‐1983
Authors: Loery Gordon , Nichols James D.
Published: May 2006

The dynamics of a wintering population of Black—capped Chickadees (Parus atricapillus) were studied from 1958—1983 using capture—recapture methods. The Jolly—Seber model was used to obtain annual estimates of population size, survival rate, and recruitment. The average estimated population size over this period was °160 birds. The average estimated number of new birds entering the population each year and alive at the time of sampling was °57. The arithmetic mean annual survival rate estimate was °0.59. We tested hypothesis about possible relationships between these population parameters and (1) the natural introduction of Tufted Titmice (Parus bicolor) to the area, (2) the clear—cutting of portions of nearby red pine (Pinus resinosa) plantations, and (3) natural variations in winter temperatures. The chickadee population exhibited a substantial short—term decline following titmouse establishment, produced by decreases in both survival rate and number of new recruits. Survival rate decline somewhat after the initiation of the pine clear—cutting, but population size was very similar before and after clear—cutting. Weighted least squares analyses provided no evidence of a relationship between survival rate and either of two winter temperature variables.
Induced Long‐Term Resistance of Birch Foliage against Defoliators: Defensive or Incidental?
Authors: Haukioja Erkki , Neuvonen Seppo
Published: May 2006

The long—term increase in foliage resistance of white birch subjected to artificial defoliation, which has been previously documented, may be a defensive response against leaf predators, or it may be passive deterioration in foliage quality due to lost nutrients. We tested these hypotheses by two experiments in which foliage quality was assayed by the growth response of a geometrid caterpillar that is the tree's major herbivore in our area. Fertilization of the soil around defoliated trees did not eliminate the change in foliage quality caused by mechanical damage, contrary to the prediction of the nutrient—stress hypothesis. Another result consistent with the defensive hypothesis was that insect damage was a more effective inducer of changes in birch foliage than mechanical damages was. Artificial defoliation was an effective inducer in a nutrient—poor but not in a nutrient—rich site; this result can be explained by either of the two hypotheses.