bluuebunny/crossref_metadata_2025 huggingface dataset:
Litter Production and Turnover in Basin Mangrove Forests in Southwest Florida
Authors: Twilley Robert W. , Lugo Ariel E. , Patterson-Zucca Carol
Published: May 2006

Litterfall, litter standing crop, and leaf decomposition of basin mangrove sites with mixed associations of Avicennia germinans, Rhizophora mangle, and Laguncularia racemosa adjacent to bay waters were compared to monospecific stands A. germinans located inland of the mixed associations. The objective was to determine whether basin mangroves with low tidal amplitude are characterized by lower litter productivity, longer litter residence times, and increased nitrogen recycling. Litterfall rates for the two mixed forests averaged 8.10 Mg°ha—1°yr—1 compared to 4.44 Mg°ha—1°yr—1 in the three monospecific sites. Peak litterfall occurred from August to October after increases in soil water salinity during June and July. Seasonal changes in surface litter mass occurred only in the monospecific forests and corresponded with higher leaf decomposition rates when tidal inundation frequency increased. As a result, surface leaf litter in a monospecific site > 200 m from the bay had a longer residence time than in two monospecific sites < 100 m inland. The rates of dry mass loss and organic carbon leaching of R. mangle leaves were lower than those for A. germinans, resulting in higher residence times of leaf litter in mixed (0.5 yr) than monospecific (0.2 yr) forests located <100 m from the bay. Leaf nitrogen decreased during senescence, and absolute nitrogen increased in leaf litter during decomposition on the forest floor. As a result, turnover rates of nitrogen in surface litter were lower than for dry mass. A comparison of litter dynamics and nitrogen recycling among riverine, fringe, and basin mangroves suggests that the relative influence of export and decomposition on litter dynamics depends on the magnitude of tidal inundation. Inland basin mangroves have low nitrogen recycling efficiency in litterfall, but higher internal recycling of litter on the forest floor, due in part to a longer litter residence time, nitrogen retranslocation prior to leaf senescence, and nitrogen immobilization during litter decomposition and peat deposition.
Effects of Selective Logging on the Behavioral Ecology of West Malaysian Primates
Authors: Johns Andrew D.
Published: May 2006

This study documents changes within a community of one nocturnal and five diurnal primate species in response to selective logging of their tropical rain—forest habitat. Groups of two diurnal primate species, Hylobates lar and Presbytis melalophos, were observed in the wild for 14 mo before and 12 mo after the onset of logging. Both species showed alterations in activity budgets following logging, spending more time resting and less time feeding and travelling. These changes may be attributable to the reduction in the availability of their preferred, more nutritious foods. Both H. lar and P. melalophos were territorial in primary forest in the study area, and there was remarkably little change in their home ranges following logging. Changes that were apparent were generally to conform to changes in habitat topography. The extent of range overlap between P. melalophos groups appeared to increase in older logged forest, however, as food resources changed from an even to a clumped distribution. The overall response of the studied primate community to selective logging appeared to be a reaction to reduced food availability and to fragmentation or other alterations of the habitat. An ability to adjust foraging strategies to cope with variation in habitat and food supply probably accounts for the continued survival of these primate populations in logged forest.
Predator Avoidance and Diel Patterns of Microhabitat Use by Larval Tiger Salamanders
Authors: Holomuzki Joseph R.
Published: May 2006

Diel patterns of microhabitat use of larval tiger salamanders, Ambystoma tigrinum nebulosum, were studied in three permanent ponds in the White Mountains of east—central Arizona during the summers of 1982—1984. Variation in the importance of risk of predation, distribution of food resources, and temperature gradients caused patterns of microhabitat use to vary among populations. Microhabitat use of larvae at Big Meadows Tanks (BMT) 1 and 2 was strongly influenced by risk of predation from adult predaceous diving beetles, Dytiscus dauricus. Adult beetles were active at night and moved almost exclusively in vegetated littoral areas, while larval salamanders occupied vegetated shallows during the day and moved to open, deeper areas at night. Field and laboratory experiments with larvae in the presence and absence of beetles demonstrated that larvae were responsive to changes in predation risk and altered their patterns of microhabitat use to minimize encounter rates with beetles. Dytiscus was essentially absent from the third study pond, Lower Cottonwood Tank (LCT), and in contrast to the Big Meadows populations, salamanders at LCT used littoral areas both day and night. Food densities and temperatures were monitored in different microhabitats of study ponds to determine microhabitats likely to be used by salamanders. Densities of zooplankton and macroinvertebrate prey were higher in vegetated shallows than in open, deeper areas at all times of day, throughout the summer sampling periods at all ponds. Larvae at Big Meadows used vegetated shallows by day, apparently because food densities and temperatures were higher than in pelagic areas, but avoided vegetated shallows at night when risk of beetle predation increased. Comparisons of dry masses of flushed stomach contents showed that feeding chronologies varied among populations and years. Salamanders balance conflicting demands of resource acquisition and risk of predation by altering their daily pattern of microhabitat use in response to periodic change in predation risk.
Fighting Behavior in Bald Eagles: A Test of Game Theory
Authors: Hansen Andrew J.
Published: May 2006

Seven predictions of evolutionary game theory were examined in field studies of foraging behavior of Bald Eagles (Haliaeetus leucocephalus) wintering in the Chilkat Valley, Alaska. A cost/benefit analysis revealed that the frequencies of two foraging strategies (hunting and stealing from conspecifics) were balanced such that the payoffs of the two were nearly equal. Asymmetries in probable correlates of fighting ability (size and, possibly, spatial position [being in the air vs. on the ground], but not age) and expected gain in victory (hunger level) influenced the outcome of contests over food. Individuals used conditional strategies: small or young birds appeared to hunt (rather than steal) relatively more than others. Pirating eagles often assessed the size and hunger level of food defenders and attacked those most likely to retreat. Contrary to prediction, ritualized displays served to advertise expected gain in victory and were good indicators of subsequent behavior. The level of escalated fighting was inversely related to resource availability. Finally, a graphical model shows that pirating frequency may or may not be influenced by changes in food abundance. The results generally support the predictions of game theory and explain several aspects of Bald Eagle foraging behavior.
Carbon Balance for Two Sphagnum Mosses: Water Balance Resolves a Physiological Paradox
Authors: Titus John E. , Wagner Daniel J.
Published: May 2006

Sphagnum fallax is generally found closer to the water table than S. nemoreum along the hummock—hollow gradient of an Adirondack bog. However, at low water contents S. fallax unexpectedly fixes carbon at higher rates than S. nemoreum, as we have previously reported. We here compare water and carbon balances for these species to resolve this puzzling contrast. S. nemoreum maintains a more favorable water balance by virtue of its greater water—holding capacity, lower rates of water loss from moist plants, and apparently more effective capillary conduction of water. The consequence is a significantly higher tissue water content in the field compared to adjacent patches of S. fallax for a wide range of dates and heights above the water table. We developed a simulation model, PEATMOSS, to evaluate the relative importance of contrasting physiological relationships and water balances of the two species. The model integrates physiological and field data to estimate 24—h carbon balance for these mosses in adjacent patches at two heights above the water table under different conditions. PEATMOSS estimated a greater carbon gain for S. fallax at the low site, where it is a clear dominant over S. nemoreum, and a markedly more favorable carbon balance for S. nemoreum at the hummock site, where S. nemoreum is common but S. fallax is infrequent. Morphological features of S. nemoreum which effect its more favorable water balance apparently confer an advantage over S. fallax when water availability is limited.
The Energetic Cost of Courtship and Aggression in a Plethodontid Salamander
Authors: Bennett Albert F. , Houck Lynne D.
Published: May 2006

The aerobic and anaerobic energetic contributions to courtship and aggression between males were measured in the plethodontid salamander Desmognathus ochrophaeus in the laboratory. Average rate of oxygen consumption and average lactate content were increased significantly above resting levels during both courtship (O2: +0.029 mL°g—1°h—1; lactate: +0.058 mg/g) and aggression (O2: +0.040 mL°g—1°h—1; lactate: +0.172 mg/g). However, these are rather small increments, representing rises of only 38—56% in oxygen consumption and only 8—23% of anaerobic capacity. The cost of a courtship bout is estimated to be 2.70 J/courting pair and is derived 90% aerobically. This value represents °1% of the daily ingested energy and secondary productivity for this species, based on estimates in a previous study. It thus seems unlikely that the behavior patterns of courtship or aggression in this species are subject to energetic limtations.
Responses of an Avian Predator and Its Isopod Prey to an Acanthocephalan Parasite
Authors: Moore Janice
Published: May 2006

This is a study of the transmission ecology of an acanthocephalan parasite (Plagiorhynchus cylindraceus) in its natural intermediate host (the isopod Armadillidium vulgare) and definitive host the (the Starling, Sturnus vulgaris). It is the first study to demonstrate in both the laboratory and the field that parasites may produce behaviorally dimorphic prey populations with respect to definitive host foraging patterns. Differences in the prevalence of such parasites could influence the outcomes of a variety of field studies involving foraging because encounter rates in such situations may not uniformly reflect prey abundances. My experiments showed that infected A. vulgare do not behave like uninfected conspecifics. In laboratory tests, infected animals were found more frequently in less humid areas, on light—colored substrate, and in unsheltered areas. Infected females rested less often and moved farther. They did not develop ovaries and did not grow as rapidly as control females. Nestling Starlings in the field had a higher P. cylindraceus prevalence than that expected if parents had foraged on isopods without respect to infection. In the laboratory, adult Starlings consumed more infected than uninfected isopods when presented with the same number of each. This foraging preference is probably because of increased encounters with infected isopods, which apparently frequent more exposed areas than do uninfected conspecifics.
The Dispersion of Eggs by a Bruchid Beetle among Scheelea Palm Seeds and the Effect of Distance to the Parent Palm
Authors: Wright S. Joseph
Published: May 2006

Larvae of an unidentified bruchid beetle develop within and kill seeds of the palm Scheelea zonensis. Only one larva can develop per seed. Hence, a selective advantage should accrue to females bruchids that oviposit on previously unattacked (pristine) fruit. On Barro Colorado Island, Panama, I performed experiments to test the following hypotheses. (1) H0: female bruchids do not distinguish between previously attacked and pristine fruit, and (2) H0: female bruchids oviposit at random among Scheelea fruit. Both null hypotheses were rejected. Female bruchids oviposit more frequently on pristine fruit, and female bruchids disperse their eggs uniformly among Scheelea fruit. Such sophisticated seed predators might search large areas of pristine seeds. As a result, seed—predation rates may fall slowly with distance from the parent palm. To test this hypothesis. I exposed Scheelea fruit at distances of 1, 8, 16 and 100 m from the nearest fruiting palm. Within 16 m, bruchid attack rates were uniformly high. However, at 100 m there was a significant decline. Other studies have found declines in seed predation rates, but only over similarly large distances. This has important implications for the mechanism by which density—dependent seed predation might contribute to the coexistence of tropical trees.
Nonlinear Relationships between Birds and Vegetation
Authors: Meents Julie K. , Rice Jake , Anderson Bertin W. , Ohmart Robert D.
Published: May 2006

We tested for the presence and importance of nonlinear relationships among bird species abundances and vegetation characteristics of the lower Colorado River valley. We transformed vegetation variables into polynomials and then ran multiple regressions, with bird densities as the dependent variables. Polynomial variables were selected in 36% of first steps and 45% of second steps in the regressions. In a significant number of cases there was a response to a polynomial variable but not to the original linear variable. Importance of curvilinear responses varied among bird species. This method offers a more comprehensive examination of responses to envirnomental gradients because unimodal and some skewed relationships can be detected.
Mammalian Seed Dispersal of Pignut Hickory during Three Fruiting Seasons
Authors: Sork Victoria L.
Published: May 2006

Seed removal by mammalian predator—dispersers was monitored weekly for Carya glabra (Juglandacea) in an aok—hickory forest of southern Michigan during three fruiting seasons. It was expected that dispersal patterns would be influenced by annual variation in seed crop size. The prediction is that large crop size enables some seeds to escape predation through satiation of dispersal agents. Within a given year, neither size of crops for individual trees nor average weekly nut fall significantly affected weekly proportion of hickory nuts removed. However, among years, proportional disappearance of nuts was slowest during the year with highest seed prodution. During all three seasons, animals removed only a small percentage for nuts, but this pattern was not the results of satiation. Instead, it is more likely due to selective removal of viable nuts. Because virtually all viable nuts were removed from the parent tree, it is concluded that dispersal in hickories is effective in preventing seedling establishment under the parent tree. However, it might be at the cost of high seed predation. Although predator satiation before dispersal was not demonstrated even during the highest seed—producing year, it is possible that postdispersal satiation may have occurred. Results of this study illustrate a relationship between seed production and seed removal that may be found in other nut—producing trees.
Annual Variability in Community Organization of Forest Herbs: Effect of an Extremely Warm and Dry Early Spring
Authors: Rogers Robert S.
Published: May 2006

The combination of drought and high daytime air temperature in north—central Indiana in early spring (mid—March to mid—April) 1981 was apparently unprecedented in the past 84 yr. In contrast, early—spring 1980 was abnormally wet, with much cooler than normal daytime temperatures. In both years (in mid—April), the composition of vernal herb communities in 10 stands of old—growth mesophytic forest was sampled in the same way and on the same calendar date (@+1 d). All sites were similar with respect to physiography, soil, and lack of recent disturbance. Mean cover of all taxa was, on average, about twice as high in 1981 as in 1980, but the proportion of total cover due to summergreen perennials was six times as high. However, between—year differences in floristic composition and frequency (proportion of plots in which a species occurs) were insignificant, regardless of phenological growth form. Though year—to—year differences in cover were large for some taxa, between—year community samples (including cover or ranks bases on cover for all common taxa) were nevertheless more similar to each other than were samples from different stands in the same year. Regarding shoot and inflorescence development, all growth forms were more advanced in 1981, but as in the case of cover, the summergreen perennials showed much greater year—to—year differences than the strictly vernal growth forms (ephemeroid perennials and "winter" annuals). An exception was the ephemeroid Dicentra, both species of which were largely fruiting and beginning to senesce in 1981 but had just begun to flower in 1980.
Contrasting Water Relations of Photosynthesis for Two Sphagnum Mosses
Authors: Titus John E. , Wagner Daniel J. , Stephens Mark D.
Published: May 2006

Sphagnum fallax and S. nemoreum differ in their vertical distribution above the water table on hummocks in Bloomingdale Bog (Adironkack Mountains, New York), and both exhibit decreasing water content with increasing height above the water table. We tested the prediction that S. nemoreum, a species better developed on hummock tops, would photosynthesize at greater rates when relatively dry than would S. fallax, which is more abundant in hollows and on hummock bases. Net photosynthesis declined sharply at tissue water contents (fresh—/dry—mass ratio) below 7.2 for S. fallax and 8.9 for S. nemoreum collected in spring. These values fell to 5.1 and 7.4, respectively, for plants collected in late summer. Thus both species exhibit adaptive seasonal acclimation, as reflected by the maintenance of relatively high net photosynthetic rates to lower water contents after a dry summer. Neither species showed significant response differences when collected from different heights above the water table. In direct contradiction to our hypothesis, Sphagnum fallax fixed carbon at greater rates than S. nemoreum at low water contents for both spring and summer collections. This physiological contrast appears inconsistent with observed field distribution patterns for these species.
Littornia and Fucus: Effects of Herbivores, Substratum Heterogeneity, and Plant Escapes During Succession
Authors: Lubchenco Jane
Published: May 2006

The mid—zone rocky intertidal community at protected and semiprotected areas in New England is characterized by a few, relatively small—bodied herbivore species. The effects of gastropod herbivores, primarily Littorina littorea, on secondary succession in the community were experimentally investigated. These periwinkle snails preferentially consume early successional, ephemeral algae such as Ulva lactuca L., Enteromorpha spp., and Porphyra spp. If not grazed, these early stages inhibit the appearance of a later successional species, Fucus vesiculous L. The effect of the herbivores on succession is to speed up the early successional sequence by releasing Fucus from inhibition by ephemeral species. Although these herbivores effectively control the ephemeral algae, they are usually unable to regulate the establishment of Fuchs. The periwinkles will readily graze small Fucus germlings (<3—5 cm long), and can prevent their successful establishment on smooth rock surfaces. However, substratum microtopography created by small crevices or pits or barnacles provides spatial refuges for small germlings. These plants quickly grow to a size at which they are less susceptible to periwinkle grazing. Thus although Fucus has a grazer—vulnerable stage, it often escapes herbivore control by virtue of spatial and size—related refuges. These escapes are herbivore—density dependent, however; unusually high number of perwinkles can prevent Fucus establishment, even when spatial refuges occur. Although the periwinkles harm young Fucus, they benefit older Fucus plants by grazing epiphytes from the blades, in lieu of the plant itself. The grazers thereby increase the persistence of individual Fucus and stabilize the community that depends upon Fucus for a habitat. The perwinkles thus play a subtle but important role in the community.
Selective Predation with Respect to Body Size in a Population of the Fish Xenomelaniris Venezuelae (Atherinidae)
Authors: Unger Philip A. , Lewis William M.
Published: May 2006

The food habits of the planktivorous fish Xeonomelaniris venezuelae (Atherinidae) in Lake Valencia, Venezuela, were studied in relation to fish size. Mean selection for major prey types and mean breadth of diet were determined for each size class of fish. The smallest fish select the rotifer Brachionus calyciflorus while successively larger fish select successively larger prey. Mean length and mean dry mass of the items eaten by the fish are directly related to fish length. Diet breadth, however, is inversely related to fish length, indicating that large fish feed more selectively than small fish. Evidence is presented which suggests that the relationship between Xenomerlaniris body size and prey selection is due to increased capture efficiency with size, and that the relationship of body size to diet breadth results from growth—related improvements in vision.
Winterkill, Oxygen Relations, and Energy Metabolism of a Submerged Dormant Amphibian, Rana Muscosa
Authors: Bradford David F.
Published: May 2006

Both larval and metamorphosed Rana muscosa (mountain yellow—legged frog) over—winter for 6—9 mo in ice—covered lakes and streams at high elevation (≤3700 m) in California and Nevada. In some winters almost all the frogs in shallow lakes (<4 m deep) die. This mortality is associated with oxygen depletion, which occurs most rapidly in shallow lakes. However, tadpoles survive for months in nearly anoxic conditions when shallow lakes are frozen to the bottom. In the laboratory at low P02, oxygen metabolism of overwintering tadpoles at 4° differed from that of frogs. The critical oxygen tension (Pc) of tadpoles (1.98 kPa) was significantly lower than for frogs (4.04 kPa). Also, when P02 was greater than Pc, the resting oxygen consumption (V02) of tadpoles partially conformed to P02, whereas the resting V02 of frogs was constant. At the atmosphere P02 of their natural environment (P02 °13.3 kPa), however, the resting V02 of tadpoles was not significantly different from that of frogs. Tadpoles apparently have two advantages over frogs during winter: (1) a greater tolerance of low P02, and (2) a reduced consumption of energy and oxygen at low P02. Unlike a number of anuran species which become dormant on land at temperatures above 4°, the resting V02 of metamorphosed R. muscosa overwintering at 4° was nearly the same as for summer—acclimated individuals in air at 4°. During 7 mo dormancy, the standard metabolic rate of both tadpoles and frogs remained constant. Resulting V02 of frogs in water at 4°, and in air at 15° was related to the 0.83—0.85 power of body mass.
Secondary Production and Organic Matter Processing by Collector Macroinvetebrates in a Desert Stream
Authors: Fisher Stuart G. , Gray Lawrence J.
Published: May 2006

Secondary production (measured as dry mass) of collector macroinvertebrates of Sycamore Creek, Arizona, estimated by the size—frequency method, is 135 g°m—2°yr—1. This high rate of production is attributed to a long growing season, continuous reproduction, rapid life cycles of major taxa, and small size at maturity. Assimilation efficiency for selected collector taxa is estimated to be 7—14% and gross growth efficiency 2—11%. At mean standing stock (3 g/m2) collectors ingest 4.2 times their body mass per day. Ingestion exceeds gross primary production, dictating both fecal reingestion and rapid turnover of fine particulate organic matter in this desert stream.
The Role of Suspended Sediments in the Nutrition of Zooplankton in Turbid Reservoirs
Authors: Arruda Joseph A. , Marzolf G. Richard , Faulk Robin T.
Published: May 2006

Reservoirs built on rivers draining watersheds are often turbid with suspended sediments. Filter—feeding zooplankton, e.g., members of the genus Daphnia, seem to be as abundant in such reservoirs as in natural lakes. Using controlled laboratory conditions, we have investigated the potential role of suspended sediments in the nutrition of Daphnia from a turbid reservoir. In three sets of experimental procedures we measured: (1) the physical effect of sediments on the ingestion and incorporation rates of algae by daphnids, (2) the ingestion rates of two sizes of clay mineral sediments particles by daphnids, and (3) the growth and survival of daphnids fed yeast and sediments with and without organic matter adsorbed onto the particle surfaces. Increases in suspended sediment concentration from 0.0 to 245 l mg/L decreased ingestion rates of 14C—labeled Chlorella vulgaris by Daphnia parvula and D. pulex by 895% and decreased incorporation rates by 99%. Sediment concentrations of 50—100 mg/L reduced the algal carbon ingested by daphnids to potential starvation levels. 65Zn—labeled fine and coarse (1.88 and 4.65 μ mean diameter) clay mineral sediment particles were fed to D. parvula, D. pulex, and D. similis. Ingestion rates of sediments by daphnids were limited at particle concentrations of 85.0 ° 106 particles/mL and were dependent on particle size, daphnid size, daphnid species, and body size. Fine particles were ingested at greater rates by D. pulex and D. parvula than were coarse particles, while large D. similis ingested coarse and fine particles at similar rates. In addition, D. pulex had higher ingestion rates in each particle size suspension than did D. parvula or D. similis. The differential ability to ingest these particles suggest a mechanism of regulating daphnid species composition if the organic matter adsorbed to these sediment particles is useful as food. To evaluate this mechanism, we adsorbed dissolved organic protein to sediment particles. When D. pulex were fed the amended sediment suspension, they grew larger than when fed control sediments, but not as large as when fed yeast. D. parvula grew equally well when fed either yeast or amended sediments. Thus, dissolved organic matter can be made available for daphnid growth by the mechanism of adsorption.
Seasonal Production Dynamics in a Guild of Periphyton‐Grazing Insects in a Southern Appalachian Stream
Authors: Georgian Ted , Wallace J. Bruce
Published: May 2006

Temporal partitioning has been found to be a predominant mode of ecological segregation among groups of systematically related stream insects. We extended this concept to a functionally similar but systematically diverse group of species. The life cycles and secondary production of six species of periphyton—grazing insects (scrapers) were studied in a fourth—order unshaded stream reach in the southern Appalachian Mountains. Total annual production (as ash—free dry mass) calculated with the instantaneous—growth rate method was 1195 mg/m2. The size—frequency estimates was 6.4% lower. Annual production (AFDM) by species ranged from 612 mg/m2 for Glossosoma nigrior to 10 mg/m2 for Goera fuscula. The production peaks of the six species occurred at separate points in the year, with very little overlap between species. Comparison with a neutral model indicated that production peaks were significantly more regularly spaced (P <.1) than would be expected by chance alone. Temporal overlap between species was calculated using density, biomass, and production. Overlaps based on density and biomass were similar (means of .173 and .171, respectively). Mean overlap based on production was significantly lower (.124). The patterns of temporal organization observed in this group of species were linked with specialized life histories. Five of the six species were univoltine, with periods of larval development (cohort production intervals [CPI] ranging from 44 to 215 d. The shortest CPIs were associated with species that diapaused in the egg (Agapetus sp.) or larval (Neophylax consimilis) stages. Summer production was dominated by G. nigrior, which had a bivoltine life cycle. Production by the spring—summer cohort of G. nigrior was 4.5 ° the production of the winter cohort. Glossosoma's bivoltinism apparently provides it with the life history flexibility to utilize the high summer periphyton production permitted by the lack of canopy cover at the study site. Seasonal production by the six species was distributed 18% in winter (January—March), 36% in spring, 38% in summer, and 8% in autumn. The seasonal distribution of grazer secondary production correlates well with previously reported seasonal dynamics of periphyton production.
Seasonal Variation of Standing Crop and Digestibility of CPOM in a Swiss Jura Stream
Authors: Barlocher Felix
Published: May 2006

Coarse particulate organic matter (CPOM, diameter > 1 mm) in a hardwater stream in the Swiss Jura reached a maximum of ≈60 g/m2 in October and November. It then declined to a low of 4 g/m2 in July. The average protein content of stream—collected leaves decreased by ≈50% between November and April. Sixty to ninety percent more protein was extractable at a pH of 11 than at a pH of 8. Digestibility of stream—controlled leaves (characterized by the release of reducing substance and amino acids from ground—up leaves exposed to gut extracts of Gammarus fossarum) also declined from November to April. Average values were considerably lower than those reported for lab—conditioned leaves; however, variability was great. Leaves generally carried active microbial carbohydrases but only rarely active proteases. In November and October, vascular—plant remains filled up to 85% of the guts of Gammarus fossarum. In spring and summer, this value dropped to 23—46%, and fine organic and inorganic particles as well as algae and mosses became more important.
Mate and Nutrient Limitation of Egg‐laying in a Polyandrous Shorebird
Authors: Lank D. B. , Oring L. W. , Maxson S. J.
Published: May 2006

Spotted Sandpipers are unusual among animals in that a female's annual reproductive effort is regulated primarily by her ability to obtain mates. Males provide most of the parental care in this species. We recorded data on the abundance of food, and on the timing, number, and size of eggs laid by marked females over a 9—yr period on an island in central Minnesota, USA. The onset of egg—laying varied from year to year in association with the abundance of flying insects early in the season. After laying began, there was no relationship between food abundance and the number of size of eggs laid, the time taken to produce a clutch, or the intervals between clutches. The rate of egg—laying per female was affected, however, by rates of nest predation and by the operational sex ratio, which became increasingly female—biased over the season. Females ceased laying eggs in early July, even in years when food and mates were still available. We conclude that nutrient availability acts as a proximate factor in determining the onset of breeding, and that it may have been ultimate factor causing cessation of egg—laying. Within the season, however, the reproductive rate of individual females is primarily determined by competitive interactions with other females for males. Thus both intra and intersexual selection have important effects on fitness in this species.
Squash Beetle Feeding Behavior: An Adaptation against Induced Cucurbit Defenses
Authors: Tallamy Douglas W.
Published: May 2006

This study tests the hypothesis that feeding behavior in the herbivorous coccinellid Epilachna borealis is an effective adaptation for avoiding facultative chemical defenses in its cucurbit host plants. Chemical analyses, feeding preference tests, fitness evaluations, and cucumber beetle assays for cucurbitacins show that (1) beetle feeding damage to zucchini leaves triggers chemical change in damaged leaves and leaves adjacent to damaged leaves; (2) this change in leaf chemistry is sufficiently potent for beetles to detect and avoid; (3) induced changes in leaf chemistry negatively affect E. borealis fitness; (4) E. borealis trenching behavior blocks, at least temporarily, the translocation of cucurbitacin defenses to feeding sites, thus preserving the palatability and quality of food resources for beetles.
Disturbance History and Serotiny of Pinus contorta in Western Montana
Authors: Muir Patricia S. , Lotan James E.
Published: May 2006

Mature Pinus contorta var. latifolia in the Bitterroot watershed of western Montana bear either predominantly serotinuous cones (cone scales sealed by a resin bond and requiring a heat treatment for opening) or nonserotinous cones. This study investigated the extent to which among—stand variation in serotiny could be explained by environmental variables, estimated fire frequency, and the nature of stand—initiating disturbance. The frequency distribution of serotiny at the stand level was biomodal, with peaks near 25 and 75% serotinous cones. Stand—level serotiny was not related to measured environmental variales and was only weakly related to estimated fire frequency. In contrast, much of the among—stand variation in serotiny could be explained by the nature of the stand—initiating disturbance, with a predominance of serotinuous trees in stands that had the originated from stand—replacing burns and of nonserotinuous trees in those that had originated from disturbances not related to fire. The disturbance regime is highly variable in time and space, and this variability, coupled with gene flow, is an important factor maintaining the polymorphism of cone type in stands.
Risk of Predation and the Structure of Desert Rodent Communities
Authors: Kotler Burt P.
Published: May 2006

Communities of granivorous desert rodents may be influenced by either predation risk or resources. To examine the influence of these factors, I manipulated illumination, using lanterns, and resources, using seeds. Foraging behavior is responsive to changes in predation risk; increased illumination reduces foraging in open areas without cover. Foraging behavior is also affected by resource enrichments. Differences among species in habitat selection are correlated with specific abilities to detect and avoid predators. The last vulnerable species, Dipodomys deserti, foraged heavily in the open and was largely unaffected by treatments; the other species of kangaroo rats and kangaroo mice (Dipodmys merriami, Dipodomys microps, and Microdipodops pallidus) also prefer the open, but responded to both risk and resource manipulations; highly vulnerable Peromyscus maniculatus was restricted to bushes, even under the best of circumstances; Perognathus longimembris was displaced from preferred microhabitat by the presence of kangaroo rats. A correlation between auditory bullar volume and use of open habitat by the various species in this community suggests that predation risk provides an axis along which habitat segregation occurs. Predation can structure communities of mobile prey when risk differs among habitats. Animals specializing in predator avoidance and in exploitation of risky environments have reduced interactions with superior competitors; this promotes coexistence.
Energy and Water Metabolism of Free‐Ranging Pocket Gophers, Thomomys Bottae
Authors: Gettinger Ronald D.
Published: May 2006

Seasonal influences on the patterns of energy and H2O metabolism by free—ranging pocket gophers, Thomomys bottae, were investigated using 3HH 18O procedures. Metabolic rates of adult, nonreproductive gophers did not differ significantly in summer, winter, or spring (CO2, 2.34 mL°g—1°h—1; 1416kJ°kg—1°d—1). Efficiency of energy assimilation (54%) by gophers consuming natural diets in the laboratory did not differ between summer and winter, even though composition of the diet changed seasonally. Calculated feeding rates (dry food, 119g°kg—1°d—1), also did not differ with season. Harvesting rates were more than two times feeding rates. Construction of energy budgets revealed that if annual vegetation is abundant, precluding the necessity for gophers to burrow extensively for food, energy is not limiting in any season. Gophers remained in H2O balance (influx ° efflux) in all seasons. However, influx was significantly greater during spring (518 mL°kg—1°d—1) than during summer or winter (256 mL°kg—1°d—1). In freeranging gophers, H2O influx was three to six times the minimum H2O flux of gophers that were maintained on H2O—restricted diets in the laboratory. In spite of their existence in arid macroenvironments, gophers appear to be "H2O—dependent." Diet selection and occupation of humid burrow systems appear to be prerequisites for existence in such habitats.
Survival of Trees After Low‐Intensity Surface Fires In Great Smoky Mountains National Park
Authors: Harmon Mark E.
Published: May 2006

The importance of bark thickness, diameter, and growth rate in determining tree survival following low—intensity of surface fires was examined in xeric pine and oak forests of western Great Smoky Mountains National Park. Bark thickness at breast and ground levels increased with dbh, and tree survival of low—intensity surface fires increased with bark thickness. Equations relating bark thickness, survival, diameter, and diameter growth rate were used to estimate the time required to grow a tree with a 50% chance of surviving a low—intensity surface fire. The mean prepark fire return interval of 10 yr favored fast—growing, thick—barked tree species over thin—barked, slow—growing species. Fire suppression since 1940 has allowed thin—barked, slow—growing species to grow into size—classes that are resistant to fire. This indicates restoration of the prepark fire interval alone will not restore the prepark forest structure.
The Effects of Canopy Shadings on Algal Recruitment and Growth in a Giant Kelp Forest
Authors: Reed Daniel C. , Foster Michael S.
Published: May 2006

The subtidal (10—15 m) assemblage in the relatively sheltered giant kelp forest at Stillwater Cove in Carmel Bay, California, consists of perennial species forming three major vertical layers: a Macrocystis pyrifera surface canopy, a dense subsurface canopy of another kelp, Pterygophora californica, and an understory of articulated and encrusting coralline algae. The kelp canopies alone or in combination can reduce bottom light to <30% (usually <1%) of surface influx. The effects of light reduction by these vegetation layers on algal recruitment and subsequent growth were determined by removing various combinations of canopies over a 2—yr period, and following subsequent changes relative to appropriate controls. Removing both M. pyrifera and P. californica canopies resulted in moderate recruitment of these species as well as of the annual brown alga Desmarestia ligulata var. ligulata. None of these algae recruited into control areas where one or both canopies were left intact. Highest brown and red algal recruitment occurred when both kelp canopies plus understory coralline branches were removed. Removal of the latter alone had no significant effect. The time of year when algal canopies were removed had little effect on the composition of subsequent algal colonization, as the recruitment of noncalcareous species occurred primarily during a short period in the spring. These results indicate that the relatively low levels of both physical and biological disturbance in Stillwater Cove allow the establishment of a few perennial algal species that inhibit their own recruitment, as well as invasion of other species, by shading. This contrasts with nearby kelp forests subjected to greater and more frequent disturbance, and characterized by a diverse assemblage of annual algal species.
Predation as an Agent of Population Fragmentation in a Tropical Watershed
Authors: Fraser Douglas F. , Gilliam James F. , Yip‐Hoi Trevor
Published: May 2006

Stream fish sometimes show mutimodal distributions, with high densities in the tributaries of a river but rarity or absence in the river itself. To assess if predation can produce such a fragmented distributional pattern on a large geographic scale, we determined the density and habitat use of a prey fish in two tropical stream watersheds, each with a barrier waterfall that split the drainage into a region with a strongly piscivorous fish and a region lacking a strong lacking a strong piscivore. In contrast to sites with the strong piscivore, the prey fish in areas above barriers showed a dramatic expansion into the main river, thereby spatially consolidating an otherwise fragmented distribution. Manipulation of piscivores in a third—order stream flanked by a series of first—order experimental streams also showed that the prey distribution expanded into the third—order stream when piscivores were excluded, and that the presence of the piscivores in the third—order stream reduced prey densities both by killing the prey and by inducing the prey to ascend cascades to enter the tributaries. Because the predator created spatial fragmentation of the prey population, we examined prey—fish dispersal in the experimental stream facility to ask whether the predator could reduce prey movement into and beyond the predator—occupied sites. As hypothesized, the experiment revealed that predators could block prey dispersal by killing prey. However, the experiment also suggested that predators may increase prey movement between tributaries by inducing shifts out of river sites. The results suggest that realistic models of dispersal by prey would need to account for effects of both predator consumption and prey behavioral responses to the predator.
Spatio‐Temporal Variation in Fruit and Frugivorous Bird Abundance in Olive Orchards
Authors: Rey Pedro J.
Published: May 2006

Fruit availability and its relation to bird abundance at different spatio—temporal scales were examined in olive orchards in southern Spain. Because olive abundance in orchards can be manipulated, this system provides an opportunity to examine the link between populations of fruit—eating birds and fruiting plants in much more detail than possible in natural systems. Olive availability varied in space and time as a result of differences in olive yield and in ripening and harvesting rates. The most abundant frugivorous birds in the orchards (Sylvia atricapilla and Turdus philomelos) were frequently able to track olive availability on both local and regional scales. S. atricapilla showed a response to even small—scale harvesting of olives by humans, distributing itself preferentially in unharvested patches. The ability of both species to track fruit availability may explain their high abundance. Other less abundant frugivores (Erithacus rubecula and S. melanocephala) showed less capacity to track olive availability. I suggest that their inability to respond to rapidly changing patterns of olive abundance may partially account for their scarcity in olive orchards. Olive orchards play an important role in maintaining frugivorous bird populations in the Mediterranean area. My data suggest that a key reason for this is great spatial and temporal variability in the availability of olives in orchards, which result in a widely scattered but temporally continuous availability of olives. The capacity of some frugivorous species to track complex spatio—temporal patterns of fruit availability was, I hypothesize, a pre—adaptive feature that allow them to flourish in the highly modified habitat of southern Spain.
Effects of Geographically Variable Thermal Environment on Bioenergetics of Mottled Rock Rattlesnakes
Authors: Beaupre Steven J.
Published: May 2006

Geographic variation in thermal environment may significantly influence the energetics of ectotherms, and thus may serve as a mechanisms for geographic variation in growth and reproduction. Thermal environment affects body temperature (Tb) that, in turn, has consequences both for the amount of time available for surface activities such as foraging, and for physiological processes such as metabolism. I studied effects of differences in thermal environment on Tb), surface use, and resting metabolism of mottled rock rattlesnakes (Crotalus lepidus) from two populations (Boquillas: BOQ, and Grapevine Hills: GVH) in Big Bend National Park, Texas. Snakes in these populations differed in growth rate and adult body size, and these differences may be related to the influence of thermal environment on energetics. During summer months, operative environmental temperatures at BOQ were hotter than at GVH. Hotter BOQ environmental temperatures resulted in °64% less time available for diurnal surfaces use (e.g., foraging) at BOQ relative to GVH. Hotter BOQ environmental temperatures also constrained the average Tb of BOQ snakes at night to be from 2°C to 4.5°C hotter than GVH snakes during July and August. Despite hotter Tb, estimated resting metabolic expenditures of BOQ snakes during July and August were similar to estimated expenditures of GVH snakes because BOQ snakes had lower mass—specific metabolic rates. Results of this study were consistent with the hypothesis of greater energy limitation at BOQ, and underscored the importance of population—specific data for understanding geographic variation in energy acquisition and allocation.
Population Dynamics in Lodgepole Pine‐Engelmann Spruce Forests
Authors: Johnson E. A. , Fryer G. I.
Published: May 2006

Pinus contorta var. latifolia and Picea engelmannii recruitment and mortality were reconstructed in 13 lower subalpine stands from age—height curves of live trees, saplings, and seedlings, and from cross—dated dead standing, fallen, and buried stems. Bole decomposition rates indicated the populations could only be reconstructed without bias during approximately the second half of a stand's history, irrespective of the stand's age. All stands traced similar recruitment and mortality patterns for the overlapping parts of their histories. Fire and understory regeneration cohorts were recognized based on risk histories. The lodgepole pine fire cohort established in the first decade after fire. Its mortality was high but decreasing in the first 10 yr, low and constant until thinning began at °25 yr, and increasing for the next °200 yr. The understory cohort recruitment started °15 yr after fire and its mortality was high, and constant with <0.5% chance of reaching the canopy. As with pine, Engelmann spruce recruited mostly in the first decade after fire, followed by low and sporadic recruitment for the next 200 yr. The mortalities of the Engelmann spruce fire and understory cohorts were constant, with the understory mortality slightly higher than the mortality of the fire cohort. As with pine, the chances of the understory reaching the canopy were small. Since the recruitment of both pine and spruce does not compensate for their mortality, the population is not self—reproducing. The population is not transient, however, because the calculated fire frequency of the area ensures burning within the life—span of the fire cohort, allowing regeneration. Consequently the long—term population dynamics of pine and spruce appear to be controlled by fire frequency.
Primary Productivity and Water Use in Native Forest, Grassland, and Desert Ecosystems
Authors: Webb Warren , Szarek Stan , Lauenroth William , Kinerson Russell , Smith Milton
Published: May 2006

The relationship between abovegound net primary production (ANPP) and water use varies significantly among ecosystem types. For both hot deserts and shortgrass prairie—cold deserts which are water limited, ANPP is linearly related to annual water use above minimum amount of water, estimated at 38 and 170 mm, respectively, needed annually to sustain each system. Once the minimum water too sustain ANPP is reached, ANPP increases an estimated 0.38 g and 1.09 g per 1000 g of additional water in the hot desert and the shortgrass prairie—cold desert. In forest systems not water stressed, ANPP was not related to water use. For grasslands representing a gradient from water stressed toward not water stressed, ANPP correspondingly declined per unit of water used. Classically evaluating water—use efficiency as annual ANPP divided by annual evapotranspiration, forests are the most efficient, 0.9 to 1.8 g ANPP/1000 g water, followed by shortgrass prairie, 0.2 to 0.7, then hot deserts, 0.1 to 0.3.