Showing papers in "Ecology in 1974"

Optimal Foraging and the Size Selection of Prey by the Bluegill Sunfish (Lepomis Macrochirus)

Abstract: The bluegill sunfish, Lepomis macrochirus, is known to select prey on the basis of size. We present evidence that this size selection is related to the optimal allocation of time spent searching for, and handling prey. A model relating search and handling time to energy return is constructed to determine the optimal breadth of diet. Prey are permitted to differ in size and relative abundance. All elements of the model are estimated from experiments with the bluegill feeding on populations constructed from size classes of Daphnia magna. Relative visibility of the different prey sizes markedly affects relative encounter rates or "effective" proportions. Effective proportions are determined empirically from feeding experiments and theoretically from reaction distance in order to correct for this bias. Search time is then manipulated by varying absolute abundance of prey. At low absolute abundance, prey of different size are eaten as encountered. As prey abundance is increased, size classes are dropped sequentially from the diet in accordance with the theory. Search and handling times are estimated for these experiments and quantitative comparisons with the model indicate these changes in diet maximize return with respect to time spent foraging.

Selection for Optimal Life Histories: The Effects of Age Structure

Abstract: The theory of optimal reproductive strategies has traditionally been studied in two ways: formal analysis of simple models that neglect the effects of age structure, and computer studies of complex life histories. Each of these approaches has disadvantages. The consequences of simple models sometimes dependmore on the nature of the simplifying assumptions than on the biological issues in question. On the other hand, computer simulations are only as general as the examples considered. The present study seeks to extend the formal analysis of optimal life histories to complex cases. I show that an optimal life history maximizes for each age class the expected fecundity at that age plus the sum of all future expected parameters. This result enables us to determine, at least inthe case of a three—stage life history, the manner in which the optimal reproductive effort at each age depends on the efforts made at the other ages, and thus, the coevolution of the various age—specific efforts. Three cases are distinguished: (1) If fertility and post—breeding survival and growth are concave functions of reproductive effort (i.e., have second derivatives that areeverywhere negative) there is a single set of age—specific reproductive rates towhich the system evolves regardless of initial conditions. This set of reproductive rates corresponds to an iteroparous life history (repeated breeding at different ages). (2) On the other hand, if fertility and subsequent growth and survival are convex functions of effort (positive second derivatives), semelparity (a single, herculean reproductive effort, followed by death) will most often evolve. However, an alternative, iteroparous life history sometimes exists, although stability considerations suggest that it may be transitory. (3)More realistic fertility and growth survival functions can generate alternative reproductive strategies that are stable since each represents a local maximum infitness. Often one of these alternatives corresponds to semelparity, the second to repeated reproduction. In such cases, the evolutionary outcome depends on initial conditions. This suggests that related species, with similar ecologies, may have very different life histories, the differences resulting from historical accidents that have trapped each on a different adaptive peak. The Salmonid genera, Salmo and Oncorhynchus, are suggested as possible examples.

Avian Community Organization and Habitat Structure

Abstract: Bird species diversity was linearly correlated with foliage height diversity and curvilinearly with total percent vegetation cover. The addition of trees in a vegetational series has a disproportionate effect on the addition of species, primarily by the addition rather than the expansion of guilds. No basic relationship of species-packing within guilds is associated with bill or body size except frequently within two-member guilds. Estimated abundance and biomass of birds does not appear to be related to productivity of the habitats, in contrast to reports from the literature. Similarity of bird species composition is not related to similarity of foliage distribution, when like study areas are compared. Avifaunas of grasslands generally differed more among themselves than did those of forests. Bird species overlaps were cor- related with foliage height overlaps only for part of the variational range for two- and three- layered habitats, and little if at all for grasslands. Width of "habitat-niche" is not related to numerical dominance, taxonomic or ecological categories. Because many of these results do not coincide with previous attempts at ecological general- ization, great care in such attempts seems strongly indicated. Studies should be made of meticulously delineated subcommunities, resource measurement, and reproductive success, as well as events in the nonbreeding season.

Predictability, constancy, and contingency of periodic phenomena'

Abstract: Temporal patterns in fluctuating physical and biological phenomena are of great interest in several fields of biology, primarily because of their importance as evolutionary constraints. To clarify and simplify the wide variety of terms used to describe aspects of temporal pattern, simple measures of predictability, constancy, and contingency are proposed. These are sufficient to describe the general characteristics of periodic phenomena. The measures are based on the mathematics of information theory. Methods of testing the statistical significance of these measures are given. Predictability, constancy, and contingency can be determined for either qualitative (categorical) or quantitative (discrete or continuous) variables measured over a period of time. Alternative patterns of seasonal flowering and fruiting of tropical trees are given as an example of a qualitative variable; precipitation data are analyzed as an example of a quantitative variable.

Phenological Events and Their Environmental Triggers in Mojave Desert Ecosystems

Abstract: Phenological events in Mojave desert systems are triggered by heavy rains (>25 mm [1 in]) The most predictable and consequential of these is a regional rain between late September and early December This rainfall event is usually the precursor of successful vegetative and reproductive growth of shrubs the next spring, and is usually necessary for all growth phenomena of herbaceous perennials and winter annuals during the following winter and spring For most plant components in most years, the growing season is synchronized within the autumn—winter—spring period, and the relative biological success each spring is dependent upon the occurrence or failure of occurrence of events of the preceding autumn Under certain conditions rainfall during other seasons may trigger growth and reproduction of the primary producers and permit at least moderate or local successes every season The relationships are stated in a flow diagram for the rainfall and phenological events, as documented for 13 yr in the Mojave desert of southern Nevada

Reconstructing forest history from live and dead plant material an approach to the study of forest succession in southwest new hampshire

Abstract: The purpose of this study is to see if it is possible to determine the course of forest succession over several hundred years by the dissection and close scrutiny of live and dead plant material. The study area was a one-tenth-acre (0.04-ha) square plot in a forest that had never been cut, located near Ashuelot in southwestern New Hampshire. Within it stem-location and growth-rate data were collected from three different classes of stems: 1) living trees, 2), dead unburied stems and stem fragments, and 3), woody remnants buried in the forest floor. The vegetational history of the plot was reconstructed from before 1665 to 1967. During this time, autogenic succession did not contribute significantly to compositional changes, whereas disturbance was an important mediator of such changes. Furthermore, changes in forest structure were often manifestations of species behavior: each tree species had a distinctive stem-distribution pattern in relation to microtopography, mode of germination, and growth. The approach seemed to provide a useful means to obtain evidence about forest change through time that may help prediction and illuminate ecological theory. Limits and modifications of the procedure are discussed.

Zooplankton Competition and Predation: An Experimental Test of the Size‐Efficiency Hypothesis

Abstract: Twelve 42—liter plankton cages were used in an alpine Colorado pond to test a size—efficiency hypothesis: to determine why small herbivorous zooplankton species tend not to coexist with large species. The size—efficiency hypothesis, that large species exclude the smaller ones through competition for food, was not substantiated. An alternate hypothesis extends the understanding of the importance of size—selective predators to include invertebrates selecting small prey. A predaceous copepod Diaptomus shoshone excluded the small Daphnia minnehaha from an association with the large D. middendorffiana within 1 mo. By implication, the predacious copepod is responsible for the absence of the small species in ponds occupied by the large Daphnia species. See full-text article at JSTOR

Competition and Regional Coexistence

Abstract: A model of the competition between two species is developed which is based on the work of Cohen (1970) and Levins and Culver (1971) and which considers the effect of competition on the colonization and extinction rates of the two species. The results are that in some cases it is possible for one species to exclude another species from a geographic region, but there is no possibility of a "priority effect" where the first species in the region can always exclude the other. Thus the equilibrium level of each species is determined by the parameters of the system and not by the initial conditions. Also, it is possible for two similar species to coexist in a region. A predator can increase the extinction rate of each species and, in some cases, permit coexistence where it would otherwise not be possible.

Responses to Starvation in the Spiders Lycosa Lenta Hentz and Filistata Hibernalis (Hentz)

Abstract: Effects of starvation were investigated in two species of spiders to gain insight on how these predators deal with an unpredictable food supply. Comparison of weights and body dimensions of individuals from field populations with those of known nutritional status showed that lack of food is a problem for field populations of both species. Adult survival times under starvation conditions averaged 208 days for the wolf spider, Lycosa lenta, and 276 days for the cribellate web-builder, Filistata hibernalis. Potential adult life spans for fed individuals were estimated to be 305 days for L. lenta and several years for F. hibernalis. Both spiders have metabolic rates significantly lower than those of other poikilotherms of similar size, and when starving, reduce their metabolic rates by 30% to 40% without any apparent decrease in their normal capabilities. The difference in survival times under starva- tion conditions of the two species was found to be inversely related to metabolic rate. This suggests that the relatively low metabolic rates characteristic of spiders as well as their capacity to reduce these rates when starving are adaptive in survival where prey are scarce. That starved individuals have the capacity to double their body weight through ingestion of large amounts of food when available may be an adaptation to their predation.

Feeding Ecology of a Temperate Insectivorous Bat (Myotis Velifer)

Abstract: The feeding behavior and ecology of the cave bat, Myotis velifer, in south- central Kansas are investigated. Emergence behavior and foraging patterns varied according to sex, age, reproductive condition, season, and colony size. Females had one synchronous period of departure in late stages of pregnancy. Two feeding periods usually were evident in summer with a major period of activity soon after sunset and a reduced secondary period before sunrise. Pregnant females emerged sooner than lactating females and adults departed before juveniles when the latter first began to fly. Adult-like emergence and foraging behavior developed in juveniles within 2 wk after flight was initiated. Adult females consumed greater quantities of food than adult males, and juveniles were less efficient at insect capture than adults. Nearly 80% of daily food consumption can be accounted for in the first 2 hr following emergence. Seasonal changes in consumption cor- responded to changing energy demands imposed by pregnancy, lactation, molt, and the avail- ability of food resources. Levels of food consumption in both sexes were lowest in spring and autumn when insect densities were low. Adult females increased their daily levels of consumption throughout most of gestation, although in the terminal days of pregnancy daily food consumption was reduced. Maximum daily levels of food consumption in adult females (approximately 25-30% of body weight) was reached near the time that young were weaned in late July and early August. Adult males achieved maximum levels of consumption (20-25% of body weight) in June, at the time molt and spermatogenesis were initiated. Young bats began foraging for insects at the age of 4 wk although their meager diet of insects was supplemented with milk for 2 wk after foraging was initiated. By the age of 6 to 0 wk their daily level of consumption increased to adult proportions. Food habits based on stomach content analysis revealed that in volume and in actual numbers, beetles (Coleoptera) and moths (Lepidoptera) comprised the major prey items in the diet. Colony size and dispersal distances may be adjusted to reduce intraspecific competition, with most individuals from large colonies dispersing nightly to greater distances than individuals from smaller colonies. Emigration of males from nursery colonies in late spring and early summer and emigration of adult females soon after young were weaned may provide a mechanism to reduce competition for available food. Small and widely-scattered transient colonies in early spring and late autumn may be important in reducing competition for food at a time when food resources are scarce.

Vegetation Patterns on a Southern Appalachian Watershed

Abstract: The vegetation on a relatively undisturbed hardwood forest watershed at Coweeta Hydrologic Laboratory, Franklin, North Carolina was sampled, and estimates of density, basal area, and above-ground biomass were computed. These vegetational parameters and five topographic variables (elevation, aspect, slope angle, distance from stream channel, and distance from water divide) were used to analyze site-species relationships on the water- shed. The primary analytical techniques used were correlation analysis and principal com- ponents ordination. Major changes in the vegetation since the introduction of chestnut blight were also examined. The vegetation on the watershed was found to be dominated by oaks, though considerable change had occurred in the vegetation composition since the appearance of chestnut blight. Total basal area on the watershed was 25.6 mVha and the total above-ground biomass was 139, 900 kg/ha. Significant correlations were found between 13 major species and one or more of the topographic variables. The ordination results revealed species groupings related to the correlation results. Distance from the stream, distance from the water divide and elevation, which produce a soil moisture gradient, were the important topographic factors determining species distribution at Coweeta.

Food-searching behavior of titmice in patchy environments'

Abstract: The food-searching behavior of titmice (Paridae) was investigated in laboratory and field to determine how effective individual birds were at locating patchy sources of hidden food. A series of three experiments was performed using tame great tits, Parus major. In Experiment 1, individual birds were offered a choice among six densities of hidden food in discrete patches. The birds learned to concentrate their search strongly on the more dense patches, and five of the six birds preferred to search at the highest density. In Experiment 2, the food distribution was altered by interchanging patches of the highest and lowest density gradually. The birds initially found fewer prey per trial, but soon recovered to near their original performance by switching their search effort to the area containing the second highest prey density. Most birds failed to respond to prey appearing where they had previously been absent. Experiment 3 varied the size of prey items among four areas containing equal numbers of hidden prey. A group of six birds learned to search selectively in areas containing larger prey and, as a result, a greater total quantity of prey. In all experiments, there were marked differences in performance by individual birds. The experiments support Royama's (1970, 1971) hypothesis that great tits distribute their search effort in relation to spatial differences in the profitability of feeding sites. Field observations on a pair of great tits and a pair of blue tits, Parus caeruleus, showed that searching behavior of wild tits was also very selective in space, at least when the birds were feeding nestlings. Birds often returned to previous capture sites and were more likely to do so when they found prey there quickly. These observations suggest that the laboratory experiments have real relevance to the food searching of wild tits. The searching capacity of great tits is discussed; it is suggested that they can approach ideal responses in stable but patchy feeding environments. Some factors leading to deviations from ideal responses are discussed.

Habitat selection of breeding birds in an east tennessee deciduous forest

Abstract: Bird populations were sampled between May 30 and July 20, 1972, on twenty- four 0.08-ha plots on Walker Branch Watershed, a primarily deciduous forest located in Anderson County, Tennessee. Univariate analysis of variance was used to test for differences in abundance categories of each bird species with respect to 28 habitat variables. Differences in habitat preferences within major bird families (Picidae, Parulidae, Paridae, and Thraupidae) were apparent from this analysis. Discriminant function analysis was therefore used to order the variables according to their strength in separating abundance categories for 13 of the more abundant bird species. This analysis indicated that some bird species were distributed ac- cording to specific habitat variables. For example, Downy Woodpecker abundance was highly correlated with the number of saplings on a plot. Distributions of other species (e.g., the Scarlet Tanager) were not strongly related to any single variable but were related weakly to a large number of variables. The results form a basis for predicting avifaunal composition changes resulting from alteration of habitat structure.

The Utilization of Dissolved Free Amino Acids by Estuarine Microorganisms

Abstract: The importance of vacteria in the cycling of carbon in the Pamlico River estuary was studied by measuring the rates of uptake of organic compounds. Our methods allowed analysis with the Michaelis—Menten kinetics equations, and both the rates of uptake of dissolved free amino acids (DFAA) and glucose as well as the percentage of carbon subsequently respired as CO2 were determined. In addition, the concentrations of the amino acids in the water were determined using ion exchange chromatography. Other tests included measurements of primary productivity and of the effects of the other amino acids in the water upon the uptake of one amino acid. There was considerable variation in the heterotrophic activity over time and distance probably caused by patchiness in distribution of plankton and dissolved compounds in the water. Although there is some competition between amino acids being taken up, the effect upon kinetics measurements is probably negligible. Tests made every 3 hr showed a coefficient of variability (CV) of the measured maximum velocity of uptake (Vmax) of aspartic acid to be only 26%, and a similar CV was found for daily samples. In several instances the uptake of one amino acid was found to be competitively inhibited by the presence of another amino acid, but the concentrations necessary to inhibit were far above natural concentrations and such effects are probably unimportant in nature. Mutual inhibition was found between the similar amino acid pairs glutamic acid and aspartic acid, threonine and serine, glycine and alanine, and leucine and alanine. Highest Vmax values were found during the summer months and early fall and ranged from a high of 69.42 mg C/1°hr for alanine in August to less than 0.20 mg C/1°hr for most of the substrates tested in the colder months. The Vmax values for glucose uptake (0.06 to 9.64 mg C/1°hr) indicate that this estuarine system is one of the most microbially—active environments tested. The DFAA were presented in the water at concentrations of from 10 to 30 mg C/1; over half of this was ornithine, glycine, and serine. The DFAA were only about 0.2% of the total dissolved organic carbon in the water. Further, seasonal variations of DFAA concentrations, generally paralleling those of primary productivity, suggested that the amino acids originated from algal excretion and the decay of algal cells. The orders of abundance and concentrations of individual amino acids were similar to those reported for other bodies of water. When the natural concentration of a substrate is known the actual velocity of uptake (Vn) or flux for that substrate may be found. Flux rates were only 1%—10% of the Vmax values in the coldest months; the highest values were found in the warmest months. At each experimental concentration of amino acid, a certain amount was taken up, and a percentage of this amount was oxidized to caron dioxide. This percentage was constant for a particular amino acid in spite of varying experimental times, substrate concentrations, and temperatures. Leucine had the lowest percent respired (13%) while aspartic and glutanic acids had the highest (50%). Failure to correct uptake data for this respiratory loss introduces significant underestimation. The production of particulate material was calculated by correcting total uptake figures for each amino acid by its characteristic respiration percentage. Over 60% of the particulate production from amino acids was by uptake of alanine, leucine, valine, serine, glycine, aspartic acid, and glutamic acid. Such particulate production averaged 0.79 mg C/1.hr for the year and ranged from 0..6 to 2.37 mg C/1.hr; this is about 10% of the rate of production by algae during the summer months. This amount of particulate organic material is a significant contribution to this estuarine food chain.

Predation and Prey Community Structure: An Experimental Study of the Effect of Mosquito Larvae on the Protozoan Communities of Pitcher Plants

Abstract: This work was designed to test the hypothesis: in the presence of predation more species will coexist in the prey community than in the absence of predation. The hypothesis may also be stated in terms of the evenness with which individuals are distributed among species. This hypothesis was tested using the communities that occur within the water-filled pitchers of the northern pitcher plant, Sarracenia purpurea L. The predator in this system is the larval stage of the mosquito, Wyeomyia smithii (Coq.). The prey community consisted of ciliated and flagellated protozoans as well as rotifers. Four approaches were used to gain information about this predator-prey system: (1) observations on the densities of the predator in the field, (2) observations on the correlation between predator density and protozoan community structure in the field, (3) field experi- ments in which both the predator density and initial protozoan community structure were controlled, and (4) observations on the development of protozoan community structure in the long-term absence of predation. The results show that there is considerable variability of predator densities in both time and space and that the protozoan community responds to these differences. The field experi- ments show that for the pitcher plant system the hypothesis must be rejected: species numbers tend to drop monotonically as predator densities increase. On the other hand, evenness (H/Hmax) does increase as predator densities increase. These patterns hold except during diapause of the mosquito larvae in the fall. These results are discussed within a general framework of factors which appear to be important for determining how predators affect prey community structure; the four possible mechanisms by which species numbers could increase with predation are outlined, and the pitcher plant system is related to each possible mechanism. The pitcher plant system has very few characteristics that would cause the system to respond to predation with enhanced species numbers. The most important characteristic leading to decreased species numbers appears to be a low level of interaction among the protozoan species. The increase in evenness in response to predation can best be explained by a shift in the factors that control species numbers from species interactions to rates of reproduction.

The Distribution and Dispersal of Pikas: Influences of Behavior and Climate

Abstract: Daily and seasonal behavior in relation to local climate was analyzed for two populations of pikas, (Ochotona princeps), representing the extremes of the altitudinal range of the species in the Sierra Nevada of California. The goal of this work was to determine the relationship of a propagule to its environment at the time of dispersal, in order to evaluate the probability of successful colonziation in different parts of the species range. Pikas at the high-altitude site (3,400 m) were active throughout the day, whereas at the warmer low- altitude site (2,550 m) they concentrated their activity in the morning and late afternoon. Field experiments suggest that when pikas are deprived of the opportunity to retreat to favorable microclimates in rockslides, they are unable to tolerate the high diurnal tempera- tures found at lower elevations. Thus, high environmental temperatures apparently constitute a major stress on dispersing individuals at low altitudes. The onset of hay storage, vocalization, and parturition, three measures of seasonality, occurred about 6 wk earlier at the low-altitude site. The timing of haying and vocalization there was correlated with the amount of precipitation during the previous winter: during dry years with little snow and an early spring pikas began and terminated their haying earlier than in wet years with a late spring. The reproductive season appeared to remain the same from year to year at the same site. The timing of dispersal of juveniles is related to the reproductive season. Most juveniles at the low-altitude site disperse during midsummer when temperatures are high and their chance of success is low. Also, during dry years most of the period suitable for gathering hay ends before a majority of the juveniles can disperse. Temperature and seasonality ap- parently have little effect on the dispersal of pikas at high altitude. At high altitude the pikas are wider ranging than at low altitude, and they occupy a greater proportion of available sites.

Aggression and Competition among Stingless Bees: Field Studies

Abstract: Many species of stingless bees exhibit complex intraspecific and interspecific aggressive behavior towards each other when they meet on flowers or artificial baits. Such aggressive encounters significantly lower the amount of time that bees spend on food sources, as well as the amount of nectar or pollen which they can gather per visit. In addition, the intensity and duration of aggression at artificial baits rises sharply with increased sugar concentration. Different species vary markedly in inherent aggressiveness. Learning and recruitment appear to reinforce the effects of aggression on the spatial separation of foraging in competing colonies. See full-text article at JSTOR

Effects of Salinity on Growth of Several Aquatic Macrophytes

Abstract: Growth rates of 10 aquatic macrophytes in various salinities under greenhouse conditions varied widely. Salt concentrations of 1.66'S and 2.50%, were toxic to Pistia stratiotes L. and Eichlornia crassipes (Mart.) Solms, respectively. Salinities of 16.65Sc, or higher were toxic to Lemna minor L., but growth of Lemna was increased by salt concentra- tions of 0.83?, 1.66S(, 2.506/c, and 3.33%, as compared to other Lemna plants grown in fertilized pondwater. Other species studied, Hydrilla v'erticillata Royle, Myriophlyllumn spica- tum L., Najas quadalupensis (Spreng.) Magnus, Vallisneria amnericana Michx., Azolla caro- liniana Willd., and Salvinia rotundifolia Willd., gradually declined in growth as salinity in- creased. Transpiration of the emersed growth form of Myriophyllumn brasiliense Camb. decreased with increasing levels of salinity, but root growth was stimulated by salt concen- trations of 0.83(,-3.33%,, presumably a response of the plant to overcome an internal water deficit resulting from the saline solutions.

Species Diversity of Decapod Crustaceans in Marine Habitats

Abstract: For 10 marine habitats the numbers of species of decapod crustacean faunas are as follows: temperate sandy beach (8), tropical sandy beach (7), tropical sand-mud beach (16), temperate Spartina marsh (14), tropical Rhizophora mangroves (17, 20), temperate man-made jetties (34), tropical Pocillopora coral (55), and tropical rocky intertidal zones (67, 78). Numbers of species were found to be little affected by temperature range, salinity range, or tidal exposure. Number of substrates is the most important factor in determining the number of species present, probably because each species can make differential use of each substrate. Latitude and longitude did not influence numbers of decapod species within habitats.

Recolonization of Hermatypic Corals on Submerged Lava Flows in Hawaii

Abstract: 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.

Reproductive effort in anoline lizards

Abstract: Lizards in the large neotropical genus Anolis exhibit an unusual mode of re- production; 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 re- productive 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 reproduc- tive 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.

Fog precipitation in coastal california forests

Abstract: Summer fog precipitation beneath coastal forests was examined at two forested sites on ridges bordering the Eel River Valley in northern California. Each site was out- fitted with bottle-funnel gauges and standard mechanical gauges placed on the forest floor and screened bottle-funnel gauges to trap fog in open areas. As much as 42.5 cm of fog water were collected beneath the forest crown during the summer fog season although differences in crown- exposure and dimension caused high variability in seasonal totals caught beneath individual trees. A typical fog precipitation event begins during late evening and ends just after sunrise. It sometimes continues for several days and produces fog drip amounts of up to 8 cm. The nutrients and water captured from drifting fog by intercepting trees, shrubs, and grasses affect water balances and nutrient cycling within such coastal ecosystems. Fog may influence species composition, and the character of the soils and vegetation of such coastal forests must certainly reflect to some degree the prevalence of summer fog.

Population Ecology of Uinta Ground Squirrels

Abstract: The behavior and ecology of Uinta ground squirrels (Spermophilus armatus) at the Utah State University Forestry Field Station northeast of Logan, Utah, were studied 1964-71 to determine the role of behavior in population regulation. In 1968 the population was reduced experimentally to about one-half the previous density. The study area consisted of a lawn area where resident squirrels more than replaced themselves, and an area of mixed shrubs and grasses where they did not. Surplus squirrels from the lawn raised the population density off the lawn. Also, habitat suitabilities varied with population densities. Hence, densities in the two areas were not proportional to habitat preferences. Before the reduction the population density fluctuated widely but the mean change for 5 yr was approximately zero. A potentially high rate of increase was curtailed by disappearance of juveniles and yearlings; juveniles tended to disperse from the natal burrow. The principal changes following the reduction were increases in percentage of yearling squirrels breeding and of juveniles remaining on the study area. Litter size and proportion of adult females breeding did not change significantly, but losses during hibernation, due in part to badger predation, decreased. Dispersal of squirrels from the study area played a key role in population regulation. Dispersers probably suffered higher mortality than sedentary squirrels, but dispersal was not necessarily maladaptive for the individual. Dispersers may have been unable to produce young at high densities; thus emigration offered the only opportunity for reproduction.

Creation of Relatively Stable Shrublands with Herbicides: Arresting "Succession" on Rights-of-Way and Pastureland

Abstract: Two decades of selective—use herbicide management on a demonstration right—of—way within the Connecticut Arboretum has resulted in a mosaic of relatively stable shrub communities and less stable herblands within the central hardwoods forest region. Areas of continuous dense shrub cover have resisted tree invasion for at least 15 yr. On abandoned pastureland shrub clones of Gaylussacia baccata, Smilax rotundifolia, and Vaccinium vacillans, from which associated tree growth was selectively removed, were analyzed for subsequent tree invasion. They have remained essentially stable for 5 yr, with virtually no tree invasion in the closed clones, as compared to pronounced invasion of the graminoid periphery of the clones. This stability can be explained in terms of Egler's "initial floristic composition" hypothesis for vegetation change, as explained in this paper. The ability of shrub communities to resist tree invasion has always belied the so—called classical concepts of succession and climax, as have the findings of other investigators. The substitution of the term "vegetation development" for "succession" and "relative stability" for "climax" would stimulate a more creative interpretation of vegetation dynamics. Creating relatively—stable shrub communities by the selective use of herbicides has practical applications in right—of—way and wildlife habitat management, naturalistic landscaping, and the maintenance of habitat diversity.

Forest Succession in Relation to River Terrace Development in Olympic National Park, Washington

Abstract: The floodway zone of the Hoh River exhibits four terrace levels of different ages, formed by erosional activity of the river on valley fills. The vegetation in this valley is in a long—term seral sequence as shown by the zonal pattern in relation to aging and development of these land surfaces. Succession starts on gravel bars, which are dominated by Alnus rubra and Salix scouleriana. The following sequential forest communities, and associated ages of land surfaces, are found: Alnus rubra on alder flats (80—100 yr); Picea sitchensis—Acer macrophyllum—Populus trichocarpa on first terraces (400 yr); Picea sitchensis—Tsuga heterophylla on second terraces (750 yr); and Tsuga heterophylla on third terraces. The latter represents the climax community for the river terrace sere, and it occurs on surfaces exposed by retreating Pleistocene alpine glaciers. The first three terraces are derived from Neoglacial alluvial fills. There is a strong correlation among zonation patterns, forest succession, age of terraces, soil moisture, and soil profile development. Available soil moisture is an important factor governing the zonal sequence. The younger land surfaces are significantly drier than the older terraces. Plants on alder flats and first terraces must withstand greater moisture stress than those of second and third terraces. As the land surface ages, the soil profile develops; deeper, more mature soils are found away from the river. The term "Olympic rain forest" is inappropriately applied to this vegetation; "temperate moist coniferous forest" is more appropriate not only for forests in the Hoh Valley, but also for the rest of the Olympic Mountains and vegetation along the northern Pacific coast.

The Effects of Space and Enrichment on a Predator-Prey System

Abstract: The prolonged coexistence of the predator Didinium nasutum and its prey Paramecium aurelia was obtained in these experiments. In a large experimental volume, predators reduced the prey population to a low density but were unable to capture them all. In small experimental volumes, all the P. aurelia were captured. In large—volume experimental systems enriched with abundant bacterial food, Didinium also captured all the prey. Thus, a large arena and the limitation of the prey population by its food supply are necessary for stable interaction and assure the survival of both predator and prey. Damped population oscillations of predator and prey occurred in the absence of refuges for prey or of physical heterogeneity. See full-text article at JSTOR

Environmental patchiness and the breakdown of leaf litter in a woodland stream

Abstract: The breakdown of allochthonous leaf litter in woodland streams occurs at the community level process which is patchily distributed. Two kinds of environmental patches were tested: types of bottom sediment and sizes of leaf pack. Four sediments, aligned along parallel environmental gradients (velocity and sediment complexity), were studied: rock, gravel, sand, and silt. Five pack sizes were studied: 1, 5, 10, 20, and 40 g. Preweighed packs of white ash (Fraxinus americana) leaflets were tied to bricks and set on the sediments. These were sampled weekly for 6 wk, and the percent dry weight lost was determined. This design was followed in each of the four seasons to test the seasonal variability in leaf litter breakdown. Analysis of variance and comparison of means show that, in all seasons, sediment and pack—size effects are highly significant (P < .001). Leaf packs of all sizes were broken down less in the silt than in the other sediments. The sediment patterns are consistent with the community level effects of physical heterogeneity and stability. Though the pack—size effects were highly variable from season to season, the degree of breakdown differentiated the leaf—pack sizes in every season, at least one size displaying major differences from the others. The seasonal patterns in breakdown reflect its temperature dependence, the breakdown increasing with increasing temperature. The community level process of leaf litter breakdown in streams is patchily distributed in space. This suggests a level of organization between the population and the community, namely the patch—specific component community.

Bat Activity and Pollination of Bauhinia Pauletia: Plant‐Pollinator Coevolution

Abstract: The relationship between the pollination biology of a tropical plant, Bauhinia pauletia, and the foraging strategies of the nectarivorous bats visiting it was studied. At least two bat species are pollen vectors, Plyllostomus discolor and Glossophaga soricina. Artibeus jamaicensis and Sturnira lilium were also captured near Bauhinia flowers. Larger bats (P. discolor) drain flowers of nectar and forage in groups, while smaller bats (G. soricina) make brief visits and forage independently. These foraging strategies should optimize energetic gain for the bats and promote outcrossing for the plant. Bauhinia pauletia is self-compatible, but is found where conditions favor outcrossing. Andromonoecism (the presence of hermaphrodite and male flowers) in this species appears to be an adaptation to pollination by large pollinators that also promotes outcrossing.

Yearly variation in larval survival of ambystoma maculatum

Abstract: Survivorship of larval Ambystoma maculatum from a single pond varied each year although the variability was not dependent on the number of eggs deposited each year. The survival depends greatly on developmental rates of the larvae, pond duration, and suitable climatic conditions at the time of dispersal. The variations in length of the larval period appear adaptive and cannot be explained by variation in dates of egg deposition. Developmental rates may be altered slightly by environmental factors.

The distribution and dispersal of pikas: consequences of insular population structure'

Abstract: The population structure of a small boreal mammal, the pika (Ochotona prin- ceps), was analyzed from demographic data and the observed spacing of populations on discrete islands of habitat in the Sierra Nevada of California. These islands of habitat varied in size and distance from one another. Not all of the islands were occupied and most seemed to contain fewer individuals than they could hold. The populations apparently represent dynamic equilibria between extinction, which was directly related to island size, and recolonization, which was inversely related to interisland distance. Distances greater than 300 m appeared to pose difficult barriers to dispersing juveniles. The study site is near the distributional boundary of pikas in this area. The birth rate is higher, adult death rate lower, and juvenile death rate higher than for other pika populations found near the center of the altitudinal or geographic range of the species. It appears that the probability of successful colonization de- creases with progressively lower elevations, until ultimately colonization is unable to offset extinction and the limit of the species range is determined.