bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Sigmodon Hispidus on Spatial and Temporal Activity of Microtus Ochrogaster: Evidence for Competition
Authors: Glass Gregory E. , Slade Norman A.
Published: May 2006

Spatial and temporal activities of cotton, rats Sigmodan hispidus, and prairie voles, Microtus ochrogaster, in an old—field habitat in northeast Kansas, USA were studied for 39 mo. During a major portion of the S. hispidus reproductive season the species were spatially segregated but co—occurred the rest of the year. Following a local extinction of cotton rats, prairie voles established a resident population in habitats formerly occupied by cotton rats that was greater than or equal to the vole population in areas which had never been occupied by cotton rats. Comparison of vole population size before and after the loss of cotton rats indicated that cotton rats produced a negative effect on vole population size during the period of spatial segregation but not during the period of spatial co—occurrence. Comparison of vole activity patterns indicated that, with the loss of cotton rats, voles shifted their activity during times when the species had co—occurred but not during periods when they were spatially segregated. Studies of behavioral interaction in a large (4 m x 4 m) arena with varying densities of vertical wires indicated that during single species tests voles and cotton rats preferred the densest areas. Their diel activity patterns were broadly overlapping. In the presence of nonreproductive cotton rats, voles continued to use the same areas as during the control tests but shifted their temporal activity reducing overlap with cotton rats. Interspecific encounters resulted in voles avoiding cotton rats even in the absence of overt aggression. In the presence of reproductive cotton rats, voles shifted their arena usage toward areas least used by cotton rats. Total nocturnal activity by voles was the same as during the control tests but was restricted to hours when cotton rats were least active. Reproductive cotton rats showed higher levels of interspecific aggression than did nonreproductive cotton rats. Voles in the presence of reproductive cotton rats showed increased frequency of serious wounds and deaths, and decreased mass when compared to voles in the presence of nonreproductive cotton rats. We conclude that cotton rats produce a negative effect on prairie vole populations but that the interaction is restricted to the cotton rats' reproductive season. Coexistence of the species appears to rely on the seasonality of the interaction, habitat heterogeneity, and the wider habitat tolerance of prairie voles.
Recolonization of Hermatypic Corals on Submerged Lava Flows in Hawaii
Authors: Grigg Richard W. , Maragos James E.
Published: May 2006

Recovery time for recolonization of coral communities on submerged lava flows in Hawaii may largely depend on exposure to sea and swell. In exposed areas, recovery time (in terms of number of species, per cent cover, and diversity) of areas decimated by lava and perhaps similar disturbances appears to be about 20 yr. At sheltered stations, more than 50 yr may be required for complete recovery. This difference in recovery time is apparently related to differences between undisturbed coral communities at exposed and sheltered stations: in exposed areas succession seems to be constantly interrupted, resulting in pioneer stages, whereas at sheltered stations reefs are more fully developed in terms of percent cover and thickness, and are thus closer to being climax coral communities; they therefore require more time for full recovery. The data, although meager, indicate that diversity increases during succession, but attains a peak value before climax is reached. The apparent decline in diversity as climax is approached may be due to interspecific competition for space, which leads to resource monopolization. Comparison of community structurewith more tropical coral reefs reveals that this pattern may apply only to physically controlled communities.
A Functional Analysis of Morphological Variation and Differential Niche Utilization in Basilisk Lizards
Authors: Laerm Joshua
Published: May 2006

The functional basis for the relationship between morphological variation and differential niche utilization within and between two species of Basilisk lizards was studied. Variation in body size and allometric changes in the size of functional elements of the hindlimb are correlated with interspecific and intraspecific differences in habitat distribution as well as the behavioral preference and functional ability for use of the adaptive strategy of running onwater. Elongated pes, orientation of the toe, and lateral toe fringes provide the drag forces necessary for support and propulsion on water. The functional size of adaptive features within and between species was compared by standardizing measurements of the functional elements as a ratio of body size. Differences in the magnitude of the functional ratios are related directly to the value of the adaptive features to provide for support and propulsion. Least—squares regressions of the relationship of the functional size of adaptive features thatcorrelate highly with observed habitat preferences as well as the behavioral preference and ability for running on water.
The Biophysical Ecology of the Alligator: Heat Energy Budgets and Climate Spaces
Authors: Spotila James R. , Soule Oscar H. , Gates David M.
Published: May 2006

Heat energy budgets were computed for the American alligator, Alligator mississippiensis, and used to generate steady—state climate space diagrams for large and small individuals. Two sides of the climate space are set by physical characteristics of the environment. The upper and lower limits of the climate space are determined by the size of the alligator, its insulation, metabolic and evaporative water loss rates, heat conducted to the ground, and its maximum and minimum sustainable body temperatures. When the alligator is at its preferred body temperature it is restricted to a small portion of its climate space. This may result in a competitive disadvantage with homeotherms that can maintain a constant internal temperature over a wide range of environmental conditions. Small alligators are more affected by wind speed than large individuals but can tolerate higher temperatures when exposed to full sunlight. Large alligators can operate outside their climate space because they can store large amounts of heat which they dump when they return within their steady—state regimes. Small individuals are closely tied to the limits of their climate space because of their small heat—storage capacity. All sizes of alligators can withstand a wide range of temperatures in a blackbody cavity. Water is the most important part of an alligator's habitat because it acts as a substitute for blackbody conditions and insures maximum utilization of an alligator's potential climate space.If alligators are deprived of water their activity is greatly restricted and their chance of survival is greatly reduced.
Reproductive Effort in Anoline Lizards
Authors: Andrews Robin , Rand A. Stanley
Published: May 2006

Lizards in the large neotropical genus Anolis exhibit an unusual mode of reproduction; all species lay a clutch of a single egg. In contrast, the more typical pattern for lizards is a multi—egg clutch in which the number of eggs increases with female size both inter— and intra—specifically. In Anolis low clutch number is associated with a potential for frequent ovipositions. Field rates for several tropical forest species are one egg every 1—2 wk. Thus, high rates of egg production coupled with a generation time of about 4 mo gives these species very high reproductive potentials. The evolution of low clutch number in relatively small tropical lizards has several non—exclusive explanations. One, which is specific to arboreal lizards (Anolis, geckonids, and some scincids), involves their adhesive toe pads, which facilitate climbing. Because pad area increases by the square of linear dimensions while body weight increases by the cube, pad area may put a limit both on lizard size and the weight of reproductive materials carried at any one time. A second and more general explanation involves the association between clutch size and climatic regime. Lizards in temperate and seasonal tropical habitats have a larger clutch number than do lizards of relatively equable tropical habitats. In these latter habitats short—term fluctuations in rainfall (associated with reproductive success) favor genotypes that are opportunistic reproducers, and relatively high predation intensity favors r—selected life history patterns. Anoline lizards are “extreme” examples of species living under such selective regimes.
Fitting the Gaussian Curve to Ecological Data
Authors: Gauch Hugh G. , Chase Gene B.
Published: May 2006

An increasing number of models in ecology involve Gaussian curves (or the lognormal, which is the Gaussian with logarithms of the abscissa values). These include models of species distributions along gradients, habitat and niche width, overlap, and packing, and the lognormal distribution of species importances. However, these models cannot be investigated quantitatively unless data can be fitted to Gaussian curves and appropriate statistics determined. Further, the Gaussian data collected by ecologists typically have special properties affecting the fitting process, notably irregular spacing of samples and truncation of the curves, thereby making ours a specialized case (as contrasted with Gaussian data in general). We conclude the best approach for our application to be a variation of parameters algorithm, and present it with a computer program in FORTRAN IV. Applications are given which test field data quantitatively against hypotheses for species distributions along environmental gradients and for dominance—diversity relationships.
Water Stress of Free‐Living Peromyscus Truei
Authors: Bradford David F.
Published: May 2006

The water relations of a Peromyscus truei population from a xeric environment, chamise chaparral, were studied in the field during two periods, midsummer and late summer, and in the laboratory. Animals were maintained in the laboratory on three water regimens that represented a gradient of water stress, but food was available ad libitum. When subjected to increasing degrees of water stress, urine osmotic concentrations increased, feces became drier, and body—water turnover rates, determined with tritiated water, decreased. When subjected to the severest water stress, diurnal torpor occurred and apparently caused a decline in urine concentration and an increase in fecal water content during the daytime. Urine osmotic concentrations and fecal water contents of midsummer mice in the field were similar to values for mice subjected to severe water stress in the laboratory. In late summer, however, the values indicated low water stress. The lower water exchange during midsummer, as determined by tritiated—water turnover, indicated that the greater water stress at this time was at least partly due to a reduced availability of water compared to late summer. During both periods food was the only apparent source of water. Mice in midsummer were feeding primarily on insects, foliage, and fungi, but during late summer, when acorns became available, they switched to this as the predominant dietary component. Acorn utilization was accompanied by onset of female reproductive activity and body weight increases for both sexes. It is suggested that water stress was alleviated by the acorn diet and was responsible for the lack of reproductive activity and depressed body weights for several months during summer.
Reproductive Strategies in Dewberries
Authors: Abrahamson Warren G.
Published: May 2006

Two predictions are made. (1) In a stable, predictable habitat when population density is low and clonal expansion is possible, vegetative reproduction should be favored. When population density is high because of crowding, plants should put a greater proportion of their resources into seed reproduction, resulting in dispersal. (2) In a temporally unstable habitat, this reproductive density response will not exist. Field studies utilizing Rubus hispidus and Rubus trivalis confirm the first prediction but not the second. In addition, cattle grazing and precipitation had a marked effect on mode of reproduction.
Optimal Niche Space of the Redwinged Blackbird: Spatial and Temporal Patterns of Nesting Activity and Success
Authors: Robertson Raleigh J.
Published: May 2006

Nesting colonies of redwings in marshes are larger and tend to be more synchronous than colonies in upland habitats of comparable area, but the duration of nesting activity is longer in large colonies. These variations in timing are probably correlated with the phenology of the vegetation in nesting habitat and not with the size of the breeding colony. Earlier nesting may be selectively advanageous because of a seasonal trend of increasing predation. The survival value to redwings of large colony size and synchronous nesting, in the colonies studied, was a reduced predation rate on a percentage basis. In most large and small colonies, the percentage of nests predated was lower during the peak of nesting activity than later. The Holling predation model is applied as a possible interpretation of predation rates on different—sized nesting colonies. Larger colonies in uplands might reduce predation on individual nests, but colony size is probably limited by the abundance of certain resources, such as availability of suitable nest—sites or food supply. Solitary pairs of smaller colonies might also suffer less predation, but genetic exchange with marsh populations, where colonial nesting is advantageous, may prevent their occurrence.
Cold‐Acclimation in Seedling Douglas‐Fir Related to Phenology and Provenance
Authors: Campbell Robert K. , Sorensen Frank C.
Published: May 2006

In October 1969, 1—year seedlings from 10 provenances growing at Corvallis were severely damaged by frost. Provenances came from eastern and western slopes of the Coast Ranges in western Washingon and Oregon. In the earliest provenance, bud set preceded frost by 5 weeks; in the latest, by 2.75 weeks. For each additional week by which bud set preceded frost, the proportion of frost—damaged seedlings decreased by 25%. For provenances setting buds in identical weeks, southern sources were more sensitive, the porportion damaged increasing by 4% per degree of decreasing latitude. Since southern sources generally set buds later and were at the same time more sensitive, they were much more severely damaged. The southernmost coastal source (Coos Bay) suffered 78% damage, the northernmost coastal (Soleduck) 10%.
Competition for Breeding Sites between the Cichlid Fishes of Lake Jiloa, Nicaragua
Authors: McKaye Kenneth R.
Published: May 2006

The temporal pattern of breeding, the bathymetric distribution of breading pairs, the microhabitat selection of breeding sites and the sizes of breeding individuals of nine species of cichlid and one eleotrid predator, Gobiomorus dormitor, were examined in Lake Jiloa, Nicaragua. For two relatively short periods of the year, during the middle of both wet and dry seasons, competition for breeding sites between these fishes was intense. Over 90% of all territories were lost prior to completing a breeding cycle. Cichlid pairs in shallow water tended to be more successful and breeding sites in these areas were more vigorously contested. The seasonal pattern of breeding was bimodal with a different species complex breeding in the wet season as contrasted to the dry. In the wet season Cichlasoma citrinellum aggressively excluded all but the two smallest species from breeding in rocky areas. In the dry season, when C. citrinellum was not breeding, all other species were able to breed, but they, in turn, were separated within that season by both depth and timing of breeding.
The Relationship between Resource Competition, Risk, and Aggression in a Tropical Territorial Lizard
Authors: Stamps J. A.
Published: May 2006

A model is proposed which relates intraspecific aggression to competition for resources and risk from aggressive encounters. Field studies of the lizard Anolis aeneus indicate that ♀ ♀ probably compete for food, ♂ ♂ for mates. Evidence includes sexual dimorphism in spacing patterns and synonymy of ♂ territoriality and mate defense through a short—term ♀ pair bond. Competition for food between ♀ ♀ of different sizes is presumed to be proportional to the overlap in prey size distributions between those ♀ ♀; competition for mates by ♂ ♂ should be equally strong among all mature ♂ ♂. By subtracting size ratio dependent risk functions from competition functions it is possible to predict aggression between animals of specified sizes. Experimental field studies tethered intruders indicate that size specific aggression in ♀ ♀ conforms closely to that predicted from the food competition model, while aggression in ♂ ♂ conforms to the mate competition model.
Foraging and Breeding Adaptations to Different Food Regimes in Three Seabirds: The Common Tern, Sterna Hirundo, Royal Tern, Sterna Maxima, and Black Skimmer, Rynchops Niger
Authors: Erwin R. Michael
Published: May 2006

Aspects of foraging and breeding ecology of the Royal Tern, Sterna[=Thalasseus]maxima, Common Tern, Sterna hirundo, and Black Skimmer, Rynchops niger, were compared in light of the food resource. Field studies conducted in 1973 and 1974 in the USA on two of Virginia's barrier islands revealed that the three species differed markedly in foraging ranges and habitat use, social feeding tendencies, and colony sizes and distribution. The investigation was designed to examine how these behavioral and ecological differences are related to the different regimes of food patterns. Analysis of beach seine records from inshore (< 50 m) waters were contrasted with haul seine and trawl collections from offshore (> 3 km) waters from both the Eastern Shore of Virginia and the Delaware Bay. Spatial variability (between sampling site variation) was found to be much greater offshore than inshore, indicating greater ‘patchiness’ of fish. Also, the availability of surfacing fish appeared to fluctuate markedly over time. In response to these food regime differences, Royal Terns, which feed further from the colony than common Terns and Black Skimmers, (1) readily formed feeding aggregations, (2) showed large daily variability in feeding the young, and (3) were the most ‘colonial’ in nest—spacing, colonial size and distribution. The strictly inshore—feeding skimmers usually fed alone, show little variability in feeding, and formed the ‘loosest’ colonies of the three species. Common Terns were intermediate in all respects. The differences in the ‘colonial tendencies’ among the species are consistent with the predictions of two earlier models relating breeding assemblages and food distribution.
Carbon Cycling in a Mixed Deciduous Forest Floor
Authors: Edwards N. T. , Harris W. F.
Published: May 2006

A study of carbon cycling within the floor of a mixed deciduous forest included estimates of litterfall, litter standing crop, root turnover, lateral root standing crop, and measurements of gaseous carbon losses from the various components. Annual carbon inputs to the system were 161 g C ° m—2 as litterfall and 733 g C ° m—2 as small roots (<0.5 cm diam). Mean annual standing pools were: 01 litter 126 g C ° m—2, 02 litter 111 g C ° m—2, small roots 340 g C ° m—2, large roots 395 g C ° m—2, and soil detritus 12,850 g C ° m—2. Annual total carbon efflux, measured in situ with an open airflow infrared gas analysis system was 1,065 g C ° m—2. Of this total, 35% was accounted for by respiration of live roots, 42.2% from root decay, 10.9% from 01 litter, and 9.7% from 02 litter. The remaining 2.2% is within the range likely associated with catabolism of root exudates and soil organic detritus. These component estimates were based on respiration rates of the individual components using a differential respirometer.
Environmental Control of Net Photosynthesis in Naturally Growing Pinus Ponderosa Laws
Authors: Helms John A.
Published: May 2006

Carbon dioxide exchange by intact foliage was monitored in the middle—crown region of 30—m tall ponderosa nine trees growing in their natural environment at 1,300 m in the Sierra Nevada of California. Characteristic diurnal patterns of net photosynthesis as a function of temperature are presented for summer conditions of low, medium, and high environmental stress. Changes in relationship between rates of net photosynthesis and factors of the environment were determined by examining the data within different time periods on days of markedly different stress conditions. Highest correlations were obtained under conditions of low stress when 80—90% of the variation in rates of net photosynthesis could be accounted for by changes in temperature and radiation alone. As general stress conditions increased, ability to predict rates of net photosynthesis decreased, with saturation vapor pressure deficit becoming the dominant factor accounting for variation. General prediction equations using data pooled from a wide range of summer conditions accounted for, at best, 65% of the variation in net photosynthesis.
Ecological Determinants of Functional Response
Authors: Real Leslie A.
Published: May 2006

Experimentally derived functional response curves for Peromyscus maniculatus preying upon European pine sawfly cocoons and wheat seeds are analyzed according to a general formula representing both hyperbolic and sigmoidal responses. The response curves were constructed under varying preferabilities of alternate prey and varying degrees of spatial contagion. The important parameter values discussed are the maximum rate of feeding (k); a searing constant (x) equal to the density of resource for which feeding is half maximal; and n, a parameter associated with the amount of "learning" exhibited by the predators. It is shown that when a low palatability alternate food is present the predator will increase both the total utilization (k) and the half—saturation (x) for the test food item being monitored, but will show little change in the degree of learning (n). On the other hand, when foods are changed from randomly dispersed to clumped in the habitat, the predators increase their total resource utilization (k) but decrease their learning (n) and half—saturation (x). The results are discussed in terms of the effect these ecological changes produce in the general behavior of the organism.
Guild Structure of the Hubbard Brook Bird Community: A Multivariate Approach
Authors: Holmes R. T. , Bonney R. E. , Pacala S. W.
Published: May 2006

We examined the similarities and differences in the foraging patterns of 22 insectivorous bird species during their breeding season in the Hubbard Brook Experimental Forest, New Hampshire, USA. Using multivariate techniques (clustering of hyperdimensional Euclidean distances, principal components analysis, and Varimax rotated factor analysis), we distinguish 4 groups of species or guilds, each of which exploits food resources in a distinctly different way. Partitioning occurs primarily by (1) foraging height and height—related characters, (2) foraging locations within the forest canopy, and (3) differential use of tree species, foraging substrates and foraging maneuvers. The results indicate that the importance of vegetation height to bird species diversity is related (1) to foraging opportunities which differ along a gradient from ground level to the upper canopy and which are roughly indexed by measures of foliage height diversity (FHD), and (2) to the presence of the supporting branch and bole framework which provides a major distinct foraging region. We suggest that foraging opportunities vary with height in a forest and are influenced by the physical and chemical characteristics of the plant species, which in turn affect the kinds and distributions of foraging substrates, the ways in which birds search for and find food, and the abundances of food resources. The implications of these findings for understanding the structure of forest bird communities are discussed.
Competition among Small Mammals in Experimentally Perturbed Areas of the Shortgrass Prairie
Authors: Abramsky Z. , Dyer M. I. , Harrison P. D.
Published: May 2006

Vegetation structure and species composition of vegetation differed on shortgrass prairie areas maintained as controls and manipulated through the application of water, nitrogen, and both water and nitrogen. Different small mammal communities formed on these 4 habitat types. Microtus ochrogaster and Reithrodontomys megalotis, rare on most habitat types of shortgrass prairie ecosystem, invaded the nitrogen / water treatment in relatively high densities. The native mammal species of the shortgrass prairie (Peromyscus maniculatus, Onychomys leucogaster, and Spermophilus tridecemlineatus) completely or partly avoided the nitrogen / water treatment. A removal experiment was conducted to test the prediction that continuing competition between the 2 invader species and the native species restricted the distributions of the latter. In this experiment, both M. ochrogaster and R. megalotis were removed from 1 plot of the nitrogen / water treatment. The second plot of the same treatment served as control for the removal experiment. Peromyscus maniculatus increased in density on the removal plot relative to the nonremoval plot. Onychomys leucogaster did not invade the removal plot; S. tridecemlineatus hibernated during most of the experiment, and its response could not be studied. The experimental results provide direct evidence that competition from M. ochrogaster affects the distribution and abundance of P. maniculatus. The results also suggest that O. leucogaster avoided the nitrogen / water treatment because of different habitat preference. Overlap indices, measured over the food and habitat dimensions of the niche, agree well with competition coefficients directly measured during the perturbation. Even though the overlap between M. ochrogaster and P. maniculatus is relatively small, the 2 species are strong competitors.
Chironomid Influence on Phosphorus Release in Sediment‐Water Microcosms
Authors: Gallepp George W.
Published: May 2006

Microcosms of Lake Mendota, Wisconsin, USA sediment and oxygenated water, maintained in darkness, were used to evaluate phosphorus increments in the overlying water as influenced by 2 species of chironomids, chironomid density and chironomid—temperature interactions. Similar systems were held in light and tested with algae present to determine if the presence of chironomids enhances algal growth. Both species, Chironomous riparius and Chironomus tentans, cause increases in phosphorus content of overlying water, with the larger C. tentans producing the greater effect. Release of total phosphorus at 20°C increased approximately linearly from 0.3—9.4 mg·—2·—1 over a range of 6 densities from 0—6585 larvae/m2. Increasing temperature from 10—20°C had little effect on phosphorus release rates in microcosms without chironomids, but in systems with C. tentans increased temperature resulted in a °10—fold increase in total phosphorus release rates. Most phosphorus released to the overlying water was soluble reactive phosphorus (SRP) which was quickly taken up by algae in lighted microcosms. Lighted controls had little total phosphorus in the overlying water or on glass substrates (wall growth), while microcosms with C. tentans contained significantly more total phosphorus in the overlying water and on glass substrates. Excretion by chironomids, rather than translocation of phosphorus from the interstitial waters of the sediment, could explain the observed data. Regardless of the mechanism, chironomids enhance phosphorus release and where abundant in the aerobic regions of lake sediments, their activities may be expected to result in a significant source of phosphorus to the epilimnetic region.
Time Budgeting and Group Size: A Theory
Authors: Caraco Thomas
Published: May 2006

This paper considers interactions between time budgets, group size and overwinter survivorship for members of avian foraging flocks. Individuals should respond to the social environment and energetic requirements by varying their allocation of time to predator detection, feeding and aggression. Predictions relate time budgets qualitatively to both the expectation and variance of foraging group sizes. Optimal group sizes for dominants and subordinates are compared to the expected group size.
Time Budgeting and Group Size: A Test of Theory
Authors: Caraco Thomas
Published: May 2006

Foraging flocks of granivorous Yellow—eyed Juncos (Junco phaeonotus) were studied for two winters to test hypothesized relationships between group size and time budgets. Required feeding time is so large that it constrains aggression. At low temperatures (high foraging requirements) a large flock forms in the area of maximal food availability. Group size decreases at warmer temperatures, since the constraints on aggression are reduced. Group size variance responds similarly. As group size increases, individuals scan less often for approaching predators. The time saved is employed to increase feeding rates, unless aggression levels are extremely high. Rates of aggressive interaction increase with group size, and with both ambient temperature and food density. Dominants apparently forage more efficiently than subordinates because of differences in habitat utilization and time allocation. These differences are consistent with the hypothesized correlation between increasing dominance and greater overwinter survivorship.
Experimental Zoogeography of Islands: Effects of Island Size
Authors: Simberloff Daniel
Published: May 2006

A controlled experiment performed on 8 small mangrove islands constituted an exact test of several biogeographic hypotheses which had rested largely on unsatisfying statistical treatments. The islands were censused for arboreal arthropods; each contained a different subset of a species pool of °500. Sections of the islands were then removed and censuses retaken after a waiting period; this procedure was repeated on four islands a second time. The results were consistent with a model which posits the islands as originally in a state of dynamic equilibrium between immigration and extinction, then re—equilibrating quickly when forced into an oversaturated condition. It was specifically demonstrated that: (1) species number increases with island size alone, independent of habitat diversity; (2) the increase with area is faster on separate islands than on increasing subsections of one island; (3) the area effect and the underlying dynamic equilibrium are not due only to an increased sample of transients and vagrants on larger islands, though there are a number of species which are particularly prone to quick extinction and which contribute disproportionately to the observed high turnover rates; and (4) prediction of the effects of decreased area on species composition can be stochastic at best, not deterministic. The equilibrium theory prediction of higher turnover rate on smaller islands could not be conclusively tested because of small sample size. Several species interactions suggested by the distributional data are so subtle that it is apparent that much more intensive work will be required to demonstrate even the existence of interactions, let alone whether they are important. It is clear that much of the dynamic equilibrium and its associated turnover in this system can be ascribed to individual species characteristics and the effects of a rigorous physical environment.
Behavioral Response of Crayfish to a Fish Predator
Authors: Stein Roy A. , Magnuson John J.
Published: May 2006

In laboratory aquaria, smallmouth bass (Micropterus dolomieui) influenced activity, substrate selection, behavior, and food consumption of crayfish (Orconectes propinquus) of different sizes and sexes. In the presence of a predator, crayfish selected substrates affording most protection, significantly modified the frequency of various behavior patterns, and reduced their overall activity. Active behavior patterns such as walking—climbing and feeding were suppressed while defensive patterns, such as burrowing and chelae display increased. Grazing by crayfish on their detrital food supply was also suppressed by bass. Degree of response of crayfish appeared correlated with liability to predation, i.e., small, vulnerable crayfish were most affected, whereas large, less vulnerable crayfish were least affected. Because crayfish ♂ ♂ have larger chelae than ♀ ♀, they apparently were better able to defend themselves against predators; consequently, less vulnerable ♂ ♂ did not modify their behavior as dramatically as ♀ ♀. In field collections crayfish exposed on the substrate were larger than those buried; fewer ♀ ♀ than ♂ ♂ were exposed. Thus, field observations correlated well with laboratory findings, suggesting that predators affect distribution and behavior of crayfish in natural communities. By affecting several trophic levels within aquatic systems, influence of predators goes beyond simple interactions of predator and prey.
Plant‐Animal Interactions: Studies of the Effects of Grasshopper Grazing on Blue Grama Grass
Authors: Dyer M. I. , Bokhari U. G.
Published: May 2006

Results of a laboratory experiment where we measured the influence of grasshoppers (Melanoplus sanguinipes) feeding upon leaves of hydroponically grown blue grama grass (Bouteloua gracillis) are presented. Performance of both the plant and animal conditions are given: growth rate of the plants held at three temperatures, amount of food ingested by the grasshoppers, digestive efficiencies, weight change of grasshoppers, the amount of litter cut, and the pH change of the root medium. The experiment indicates that thee are plant processes triggered by grasshopper feeding which result in increased energy transport levels within the plant. Most of this energy expenditure occurs in the belowground complex of the plant. Moreover, regrowth potentials of the plant on which grasshoppers had been feeding is much higher than for plants that had simply been clipped. Hence, we suggest that perhaps the largest single effect displayed by aboveground insect grazers on grassland ecosystem plants (viz., grass) is the increase in belowground respiration and root exudation.
Reduction of Mucuna Andreana (Leguminosae) Seedling Fitness by Artifical Seed Damage
Authors: Janzen Daniel H.
Published: May 2006

Removal of 1%, 5%, and 10% of the seed weight of Mucuna andreana seeds severely reduced the ability of the seedling to withstand artificial herbivory. Seed weight was removed by drilling holes in the seeds in order to mimic bruchid damage.
Territoriality and Male Mating Success in the Green Frog (Rana Clamitans)
Authors: Wells Kentwood D.
Published: May 2006

Territorial behavior of Rana clamitans was studied in an enclosed experimental pond. Males maintained territories from June through August. Most ♂ ♂ occupied more than one site during the breeding season. Most sites were occupied for < 1 wk before changing ownership, but some were occupied by a single ♂ for up to 7 wk. Large ♂ ♂ remained at individual sites longer and spent more total time in territories than small ♂ ♂. The smallest of ♂ ♂ usually acquired territories only after other ♂ ♂ had abandoned them, while larger ♂ ♂ sometimes ousted residents with aggressive behavior. Males sometimes adopted a satellite role in the territories of other ♂ ♂ and waited for sites to become available. Individual territory sites were ranked by relative quality based on the physical structure of the sites. Female choice of mates appearerd to be related to territory quality, and especially to density of vegetation in the water. Males that spent the most time in high quality territories acquired the largest number of mates. The social system of the green frog probably evolved as a result of intense ♂— ♂ competition for mates. This in turns is probably related to its prolonged summer breeding season.
Components of Diversity: Multivariate Analysis with Interaction
Authors: Alatalo Rauno , Alatalo Ritzso
Published: May 2006

We use the effective number of species as a measure of diversity of a community. Shannon's function H' and other logarithmic or multiplicative indices of diversity give components of diversity which are difficult to interpret. Exp(H') and the reciprocal of Simpson's index, which measure the effective number of species, and linearly related to the number of species. The effective number of species is partitionable into components determined by resource dimension and their interaction. Components of diversity measure differences which are found by using various niche axes alone and together. Our method allows the analysis of the relations between the overall structure of the community or guilds and their resource space. The residual component of diversity measures the niche overlap of species in respect to the resource dimensions studied.
The Relation of Population Density and Adrenal Gland Weight in Cycling and Noncycling Voles (Microtus)
Authors: To Leleng P. , Tamarin Robert H.
Published: May 2006

Changes in adrenal weight in individuals of the beach vole, Microtus breweri, and its close mainland relative, the meadow vole, Microtus pennsylvanicus, were investigated over a 4—yr period. Covariance analyses indicated no significant increase in adrenal weight concomitant with increase in population density of M. pennsylvanicus, while significant increases in adrenal were correlated to increase in populations size in M. breweri. Since a 3— to 4—yr population cycle is not observed in M. breweri but is evident in M. pennsylvanicus on the mainland, it seems that Christian's behavioral—endocrine mechanism is not limiting the population growth of these voles.
Experimental Studies of Microcrustacean Competition, Community Composition and Efficiency of Resource Utilization
Authors: Neill William E.
Published: May 2006

Studies of perturbed laboratory microcosm communities composed of algae and competing herbivorous microcrustaceans were conducted to assess the role(s) of various species compositions and patterns of resource consumption on the efficiency of resource utilization. Equilibrium microcosm communities, consisting of four competing species, three cladocerans, and an amphipod, were perturbed by different intensities of highly size—specific fish predation that resulted in altered species compositions (two or three additional species) and new equilibrium densities. Analyses of food particle consumption patterns, spatial distributions, and life history characteristics under the different predation intensities indicated the importance of microhabitat and food specializations in permitting coexistence of some species but exclusion of others. Age— and size—specific competition for limiting small (3—6 μm) particles was especially important among young animals at low predation levels, whereas under high predation, competition for larger particles among adults was more important. Analyses of particle uptake efficiencies in the different communities revealed very uneven use of available resources when the presence of efficient competitors for some foods produced developmental bottlenecks among the young of competing specis. Resource utilization efficiencies were much less variable at equilibrium when predation reduced competition on the young. The potential general importance of age— and/or size—specific competition in reducing the efficiency of resource utilization in communities of organisms other than terrestrial homeotherms is suggested and contrasted to the current community models of competition.
Foraging Patterns and Resource Utilization in Seven Species of Bats in a Seasonal Tropical Forest
Authors: Heithaus E. Raymond , Fleming Theodore H. , Opler Paul A.
Published: May 2006

Many tropical bats eat fruit, nectar, and pollen, and many tropical plants are pollinated or dispersed by bats. These groups make up a coevolved system that illustrates the effects plants can have on animal populations, and conversely, the effects animals can have on plant populations. This paper reports a 2—yr intensivie study of one bat—plant community in a seasonal Costa Rican forest. Seven common phyllostomatid bat species visited flowers or fruits. These were Glossophaga soricina, Phyllostomus discolor, Artibeus jamaicensis, Artibeus lituratus, Sturnira lilium, and Carollia perspecillata. The incidence of nectar ivory was high among these species, even among the species previously considered to be frugivores. Flora resources were seasonally abundant and competition for these resources appeared minimal during the period of peak abundance, but only G. ssoricina was nectarivorous during the period of low flower abundance. Fruit resources were more evenly available through the year and were more finely divided among the species of bats. There was a correlation between size of bat and the average size of fruits eaten. To the extent that competition for food has influenced the structure of this bat community, competition for fruits was more important than competition for nectar and pollen in determining species diversity. Resource distributions through space and time also infuenced bat foraging and reproductive behaviors. Small species of bats feed on resources of high abundance, whereas large species utilize resources that are patchy in time and space. The latter species probably forage in groups to maximize foraging efficiency. Reproductive behavior is seasonal and correlated with resource abundance. The flowering periods of plant species tend to be displaced, suggesting competition among plants for bat—pollinator services. A combination of the timing of plant—reproductive behavior and bat foraging characteristics promotes long—distance outcrossing and seed dispersal. These are critical factors in determining the low—density propulations characteristic of many tropical plant species.
Some Demographic Consequences of Food Shortage for the Predator, Notonecta hoffmanni
Authors: Fox Laurel R.
Published: May 2006

The freshwater hemipteran predator, Notonecta hoffmanni, has one generation per year. Eggs are first laid in late winter and begin hatching in April; most nymphs hatch in mid—June. A short period of heavy mortality of instar I nymphs in eary summer is followed by a more gradual decline in the numbers of older individuals until autumn. The mortality of young nymphs shifts the age—distribution towards older individuals early in summer and increases the changes for the first nymphs hatched in spring to survive and breed successfully. Three alternative hypotheses about the causes of nymphal mortality are proposed and I argue that the primary cause is a reduction in food availability resulting in increased cannibalism. Reduction in spatial refuges also influences cannibalism rates. Field and laboratory experiments show that delayed reproduction by young adults is related to food availability. I suggest that a second generation of N. hoffmanni is possible if sufficient food were available when young adults mature in August.
Feeding Rates and Population Growth
Authors: Rapport David J. , Turner James E.
Published: May 2006

Numerous studies of natural populations have generated data relating foraging activities, the quantity and quality of available food resources, and population dynamics. In order to interpret these data we develop a comprehensive theorectical framework by constructing a model of foraging behavior and population growth in terms of energetic cost—gain functions. With total energy costs and gains of foraging viewed as functions of the quantity of food consumed per unit time, a simple graphical model indicates a range of profitable consumption rates. The organisms's choice of feeding rates within this range depend upon the foraging strategy adopted. A foraging strategy that mixmizes net energy gain results in a higher consumption rate than a strategy that minimizes the time spent foraging. As the population increases, energy costs of foraging may rise, and this results in a reduction of feeding rates by energy maximizers while time minimizers increase their feeding rate. As a population approaches its carrying capacity, the consumption rates of energy maximizers and time minimizers converge. An explicit dynamic model indicates the relationship between the population growth and the energetic parameters underlying its foraging activities. For example, the biotic potential, r, is found to be proportional to the maximum net gain from a numit of resource and to the equilibrium consumption rate. Comparing the population growth of "optimal foragers" with other strategies in the model the optimal foraging strategy yields a more rapid appoach to equilibrium.
Granivory in North and South American Deserts: Rodents, Birds, and Ants
Authors: Mares Michael A. , Rosenzweig Michael L.
Published: May 2006

Experiments which measure seed removal rates of ants, birds, and mammals were conducted in the Sonoran Desert of North America and the Monte Desert of South America. Rodents were the primary consumers in North America, but ants also took large amounts of seeds there. Ants were the major granivores in the Monte, where mammal seed consumption was insignificant. Birds were relatively unimportant consumers in both deserts. Total seed removal rates were more than an order of magnitude larger in the Sonoran Desert. These results are much in contrast with the great overall similarity of the 2 systems in climate and flora. The extinction, 1 or 2 million yr ago, of a marsupial family, Argyrolagidae, which appears to have been the ecological equivalent of the rodent granivores, Heteromyidae, may have cause the differences in granivory either because the Argyrolagidae were mutualistic with the plants or, in an evolutionary sense, with the granivorous ants.
Effect of Adult Townsend Voles (Microtus Townsendii) on Survival of Young
Authors: Boonstra Rudy
Published: May 2006

To test the hypothesis that adult voles reduce the survival, growth, and maturation rates of young voles, cohorts of young were introduced at 6—week intervals throughout the spring, summer, and fall of 1975 onto an unmanipulated area, a ♂ removal area, and a total removal area. Young survived best on the total removal area but poorly on both other areas. Growth in young ♂ ♂ was directly related to the density of adult ♂ ♂. The weight at which ♀ ♀ attained sexual maturity was directly related to the density of adult ♀ ♀ but not to the density of adult ♂ ♂. Males showed a similar relationship in response to the density of adult ♂ ♂. I conclude that adult ♀ ♀ reduce the survival of young. Further study of ♀—young interactions is necessary to determine the mechanisms involved.