Showing papers in "Oecologia in 1981"

Similarity indices, sample size and diversity

Abstract: The effect of sample size and species diversity on a variety of similarity indices is explored. Real values of a similarity index must be evaluated relative to the expected maximum value of that index, which is the value obtained for samples randomly drawn from the same universe, with the diversity and sample sizes of the real samples. It is shown that these expected maxima differ from the theoretical maxima, the values obtained for two identical samples, and that the relationship between expected and theoretical maxima depends on sample size and on species diversity in all cases, without exception. In all cases but one (the Morisita index) the expected maxima depend strongly to fairly strongly on sample size and diversity. For some of the more useful indices empirical equations are given to calculate the expected maximum value of the indices to which the observed values can be related at any combination of sample sizes. It is recommended that the Morisita index be used whenever possible to avoid the complex dealings with effects of sample size and diversity; however, when previous logarithmic transformation of the data is required, which often may be the case, the Morisita-Horn or the Renkonen indices are recommended.

Coping with Herbivory: Photosynthetic Capacity and Resource Allocation in Two Semiarid Agropyron Bunchgrasses,

Abstract: Agropyron desertorum, a grazing-tolerant bunchgrass introduced to the western U.S. from Eurasia, and Agropyron spicatum, a grazing-sensitive bunchgrass native to North America, were examined in the field for photosynthetic capacity, growth, resource allocation, and tiller dynamics. These observations allowed identification of physiological characteristics that may contribute to grazing tolerance in semiarid environments. A uniform matrix of sagebrush, Artemisia tridentata, provided an ecologically relevant competitive environment for both bunch-grass species. Physiological activity, growth, and allocation were also followed during recovery from a severe defoliation treatment and were correlated with tiller dynamics. Potential photosynthetic carbon uptake of both species was dominated by stems and leaf sheaths during June, when maximum uptake rates occurred. For both species, water use efficiency of stems and sheaths was similar to that of leaf blades, but nitrogen investment per photosynthetic surface area was less than in blades. In addition, soluble carbohydrates in stems and sheaths of both species constituted the major labile carbon pools in control plants. Contrary to current theory, these findings suggest that culms from which leaf blades have been removed should be of considerable value to defoliated bunchgrasses, and in the case of partial defoliation could provide important supplies of organic nutrients for regrowth. These interpretations, based on total pool sizes, differ markedly from previous interpretations based on carbohydrate concentrations alone, which suggested that crowns contain large carbohydrate reserves. In this study, crowns of both species contained a minor component of the total plant carbohydrate pool. Following defoliation, A. desertorum plants rapidly reestablished a canopy with 3 to 5 times the photosynthetic surface of A. spicatum plants. This difference was primarily due to the greater number of quickly growing new tillers produced following defoliation. Agropyron spicatum produced few new tillers following defoliation despite adequate moisture, and carbohydrate pools that were equivalent to those in A. desertorum. Leaf blades of regrowing tillers had higher photosynthetic capacity than blades on unclipped plants of both species, but the relative increase, considered on a unit mass, area, or nitrogen basis, was greater for A. desertorum than for A. spicatum. Agropyron desertorum also had lower investment of nitrogen and biomass per unit area of photosynthetic tissues, more tillers and leaves per bunch, and shorter lived stems, all of which can contribute to greater tolerance of partial defoliation. Greater flexibility of resource allocation following defoliation was demonstrated by A. desertorum for both nitrogen and carbohydrates. Relatively more allocation to the shoot system and curtailed root growth in A. desertorum resulted in more rapid approach to the preclipping balance between the root and shoot systems, whereas root growth in A. spicatum continued unabated following defoliation. Nitrogen required for regrowth in both species was apparently supplied by uptake rather than reserve depletion. Carbohydrate pools in the shoot system of both species remained very low following severe defoliation and were approximately equivalent to carbon fixed in one day by photosynthesis of the whole canopy.

The filtration apparatus of Cladocera: Filter mesh-sizes and their implications on food selectivity

Abstract: The filtering apparatus of eleven Cladoceran species was studied. The distances between the setulae, which act as filters, were measured. Among adult individuals, they vary from 0.2 μm in Diaphanosoma brachyurum to 4.7 μm in Sida crystallina. Species can be grouped according to the mesh-sizes, as “fine mesh filter-feeders”: Diaphanosoma brachyurum, Ceriodaphnia quadrangula, Chydorus sphaericus, Daphnia cucullata and Daphnia magna; “medium mesh filter-feeders”: Daphnia galeata, D. hyalina. D. pulicaria, Bosmina coregoni, and “coarse mesh filter-feeders”: Holopedium gibberum and Sida crystallina. In Daphnia hyalina, the distances between setulae increase from 0.3–0.4 μm in small juveniles, to 0.8–2.0 μm in adults. In Daphnia magna, the mesh-size of the filter does not increase significantly with growth. There is good evidence that the relative abundance of the filter-feeding types varies with the trophic state of the lake. In oligotrophic lakes the “coarse mesh filter-feeders” usually dominate throughout the year. The seasonal succession of zooplankton species in eutrophic lakes can be interpreted as a succession of feeding types; during winter “coarse mesh filter-feeders” dominate, while “fine mesh filter-feeders” are most abundant during summer phytoplankton blooms. Our results support the hypothesis that the species composition of filter-feeding zooplankton is strongly influenced by the amount of suspended bacteria which are available as food only for filter-feeding species with fine meshes.

Relative growth rates and the grazing optimization hypothesis.

Abstract: A mathematical analysis of the changes in plant relative growth rates necessary to increase aboveground production following grazing was conducted. The equation derived gives an isoline where production of a grazed and ungrazed plant will be the same. The equation has four variables (mean shoot relative growth rate, change in relative growth rate after grazing, grazing intensity, and recovery time) and may be analyzed graphically in a number of ways.

Why are adaptations for long-range seed dispersal rare in desert plants?

Abstract: The rarity of long-range seed dispersal (telechory) and commonness of antitelechory in desert plants are examined in light of contemporary mathematical theories of the evolution of dispersal and germination behaviors. Analysis of dispersal 3-habitat relationships in the flora of Israel supports the general trend towards atelechory in deserts; in particular epizoochory and tumbleweeds are practically absent from the desert and heterocarpy is centered in the Mediterranean region. In contradiction to the accepted "mother-site" theory, we find that (a) there is a high turnover in microscale spatial pattern among antitelechoric species; (b) antitelechoric (especially basicarpic) species are widespread and dominant in the desert vegetation of Israel; (c) amphicary and geocary are rare in the desert flora of Israel.We argue that the openness of desert vegetation and the patterns of climatic variation favor atelechory while antitelechory is generally a side-effect of mechanisms whose adaptive value is not directly related to dispersal. Thus for example the desert plants of Israel have evolved a variety of dispersal-restricting seed-containers that protect the seed from predation and flooding, regulate the within-season timing of germination, and spread dispersal and germination over several years.

Sociality as a life-history tactic of ground squirrels.

Abstract: Multi-variate analysis of life-history traits of 18 species of burrowing sciurids indicates that reproductive effort is determined by body-size energetics. Other traits, such as age adult weight reached, age of dispersal, length of time of gestation, were significantly correlated with body size. A principal component analysis suggested that the complex of life-history traits could be reduced to four components: body size (=weight), seasonality, specific reproductive effort, and maturity. The variation in the sociality index was best explained by age of first reproduction and age adult weight reached. Generally, species are more social when large body size combined with a relatively short growing season is associated with delayed dispersal and occurs in those species typically breeding for the first time at age two or older. Sociality in these species may have evolved through retention of daughters within the maternal home range as a means of continuing reproductive investment beyond weaning.

The effect of the thermal environment on the ability of hatchling Galapagos land iguanas to avoid predation during dispersal

Abstract: During the month of February 1979, several hundred hatchling land iguanas (Conolophus pallidus) were observed emerging from their natal burrows in a 2 ha communal nesting area on Isla Santa Fe, Galapagos Islands. During this emergence, as many as nine Galapagos hawks were observed to patrol the nesting area and attack hatchling iguanas. The hypothesis that the ability of hatchling land iguanas to escape predation could be influenced by the interaction of the physiological state of the lizards and the thermal environment was analyzed using (1) empirical data on the effect of body temperature (T b) on locomotory ability of iguanas and (2) biophysical modeling of the T b's of hatchlings under natural conditions. This hypothesis was tested by assessing the success of natural hawk attacks on lizards exposed to different thermal environments. During those periods when predicted T b's of hatchlings were always <32°C, (at which temperatures land iguanas were shown to have less than maximal ability to sprint rapidly) hawks were successful in 67% of the observed attacks. However, when T b's of hatchlings were always ≧32° C, hawks were successful on only 19% of observed attacks. During periods when hatchling T b's could be <32° C or 32–40° C (depending upon which microhabitat the hatchling occupied before the attack), the hawks were successful in 46% of the observed attacks. These data indicate that the physical environment, as mediated through the physiological state of the lizards and to correlated locomotary abilities, significantly affects the ability of hatchling land iguanas to escape predation.

On the survival of populations in a heterogeneous and variable environment

Abstract: The survival time of small and isolated populations will often be relatively low, by which the survival of species living in such a way will depend on powers of dispersal sufficiently high to result in a rate of population foundings that about compensates the rate of population extinctions. The survival time of composite populations uninterruptedly inhabiting large and heterogeneous areas, highly depends on the extent to which the numbers fluctuate unequally in the different subpopulations. The importance of this spreading of the risk of extinction over differently fluctuating subpopulations is demonstrated by comparing over 19 years the fluctuation patterns of the composite populations of two carabid species, Pterostichus versicolor with unequally fluctuating subpopulations, and Calathus melanocephalus with subpopulations fluctuating in parallel, both uninterruptedly occupying the same large heath area. The conclusions from the field data are checked by simulating the fluctuation patterns of these populations, and thus directly estimating survival times. It thus appeared that the former species can be expected to survive more than ten times better than the latter (other things staying the same). These simulations could also be used to study the possible influence of various density restricting processes in populations already fluctuating according to some pattern. As could be expected, the survival time of a population, which shows a tendency towards an upward trend in numbers, will be favoured by some kind of density restriction, but the degree to which these restrictions are density-dependent appeared to be immaterial. Density reductions that are about adequate on the average need even not occur at high densities only, if only the chance of occurrence at very low densities is low. The density-level at which a population is generally fluctuating appeared to be less important for survival than the fluctuation pattern itself, except for very low density levels, of course. The different ways in which deterministic and stochastic processes may interact and thus determine the fluctuations of population numbers are discussed. It is concluded that some stochastic processes will operate everywhere and will thus necessarily result in density fluctuations; such an omnipresence is much less imperative, however, for density-dependent processes, by which population models should primarily be stochastic models. However, if density-dependent processes are added to model populations, that are already fluctuating stochastically the effects are taken up into the general, stochastic fluctuation pattern, without altering it fundamentally.

Evolution by individuals, plant-herbivore interactions, and mosaics of genetic variability: The adaptive significance of somatic mutations in plants.

Abstract: Differences in the pattern of organization of organisms may lead to different patterns of evolution, genetics and ecology, Plants and animals differ in their fundamental patterns of organization. Plants consist of a series of repeating units that compete with one another, while animals consist of mutually interdependent systems that cannot compete. As a result, plants may be able to take advantage of somatic mutations in ways that are not available to animals. Somatic mutations arising in plants can be inherited by naturally occurring mechanisms of sexual and asexual reproduction. Long life span, large clone size, and the complete regeneration of buds each year may permit an indivdual plant or clone to evolve. Plants may even develop as mosaics of genetic variation. Evolution by individual plants and/or development as mosaics of genetic variation may prevent herbivores from breaking the defenses of their host plants. This evolution may also result in greater “fine tuning” to local environments leading to ecotypic variation.

Tree species preferences of foraging insectivorous birds in a northern hardwoods forest

Abstract: Birds searching for insects in the canopy of a northern hardwoods forest depart significantly from random in their use of tree species, even when these trees are generally similar in life form. All 10 foliage-dwelling bird species in the Hubbard Brook forest showed preferences for Yellow Birch, most had an aversion to Beech and Sugar Maple, and a few had special preferences for conifers or White Ash. Birds that glean prey from leaves had stronger tree species preferences than those that often hover for their prey, and were more influenced by tree species differences in foliage structure. The less common bird species and those for which northern hardwoods are marginal habitat had the most pronounced tree-species preferences. Food densities which are higher on Yellow Birch and specific adaptations to foraging in trees with particular foliage structures are considered major factors responsible for the observed tree species preferences. The implications of these findings for bird community structure and for forest management practices are discussed.

Biogenic rock varnishes of the negev desert (Israel) an ecological study of iron and manganese transformation by cyanobacteria and fungi.

Abstract: The ecology of the microflora, which produces rock varnishes in the Negev is described. It is shown that biogenic rock varnishes may form within relatively short periods (1967–1981) on places where pre-existing varnishes were eliminated. Rock varnishes are thin coatings, mainly composed of Fe and Mn hydroxides and clay material. Biogenic rock varnishes form at places where “microbial weathering fronts”, which destroy the rock substrate, advance extremely slowly or come to stillstand, thus enabling the development of biogenic “protective coatings”. Rock varnish is mainly produced by the activity of often lichenised epi- and endolithic cyanobacteria, chemoorganotrophic bacteria, and fungi, which are sometimes associated with the still debatable Metallogenium symbioticum. In cases, where “microbial weathering fronts” reach harder bedrocks during their progress, the then developing rock varnish plays a protective role for the microflora beneath the varnish in formation. This microflora otherwise would be directly exposed to the harsh desert conditions and could not survive. Biogenic rock varnishes are characteristic examples of a microbial ecosystem, which adapted itself to one of the most extreme environments on this planet, i.e. high irradiation, extremely low water activity, no chances of deplacement upwards or downwards and in addition the highest daily changes in temperature and irradiation and humidity one may observe in natural environments. It seems, that the “solution front community” which is trapped on increasingly harder and resistant rocks has evolved the capacity to protect itself from the harsh environmental conditions by the creation of rock varnish as a kind of armour shielding it from the extremes of environmental stress.

Fitting and using growth curves.

Abstract: A technique is presented for fitting and analyzing growth patterns using Gompertz, power, and exponential curves. Data collection involves measuring growth rate as a function of size. This is useful because growth rates at many different sizes can be measured at the same time, which removes the effect of environmental change from the observed growth pattern. Using size instead of age as the independent variable is important because size is usually more closely related to growth rate than is age. The particular technique presented here yields estimates of the variance of the curve parameters so that growth curves for different populations can be compared.

Effects of interactions between algae and grazing gastropods on the structure of a low-shore intertidal algal community.

Abstract: At low levels on shores in New South Wales, foliose algae are abundant and often occupy all substrata; microalgal grazing gastropods are rare or absent. At higher levels, foliose algae are sparse or absent and grazing gastropods are abundant. Hypotheses for the causes of the lower vertical limits of distribution of these grazers include the effects of increased predation or the deleterious physiological effects of increased period of submergence at lower levels on the shore. Alternatively, the presence of the algae, because they occupy space and deprive the grazers of substratum for feeding, may prevent the downward movement, or survival of the grazers at low levels. Under the first two of these hypotheses, algae are able to colonize and grow in low-shore areas as an indirect result of factors which remove grazers. Under the third hypothesis, the algae are directly responsible for the lack of grazers.Experimental clearings of the low-shore algae and introductions of the mid-shore limpets Cellana tramoserica and Siphonaria denticulata were used to test these hypotheses. C. tramoserica grazes microalgae and removes them from the substratum, preventing colonization. S. denticulata, in contrust, crops the algae, leaving a visible cover of algae on the substratum, which can grow rapidly. Because of its method of feeding, S. denticulata had no measurable impact on the rates of colonization, nor on the dry weights of algae, compared with those of ungrazed areas. C. tramoserica could keep cleared areas tree from foliose algae, but only when the limpets were mainfained in great density (10 per 900 cm2). They were less effective where wave-action was greater.Neither species of limpets could survive when placed onto beds of mature algae, because they had no substratum on which to cling and were swept away by the waves. C. tramoserica did not invade clearings below their lower limit of distribution where they had to move over a bed of foliose algae. Few C. tramoserica moved directly downshore into cleared areas. When placed on bare rock within low-shore beds of algae of different ages, S. denticulata remained amongst the algae and maintained their tissue-weights. Few C. tramoserica remained in areas with well-developed algae, compared with areas having sparse algal growth. Those Cellana which remained amongst well-developed algae lost weight, whereas limpets in areas with less algal growth mammtained their weights. In experimental cages in low-shore beds of algae, where the limpets were inaccessible to potential predators, C. tramoserica lost weight and died. On cleared areas they survived for many weeks, but lost weight and died as algae grew and covered the substratum. In the absence of predation, the micro-algal grazer C. tramoserica could not survive in lowshore areas because algae grew too fast and occupied the substratum, making it inaccessible for the limpets to graze; the algae, once grown beyond small sporelings, are not a suitable food-source for C. tramoserica, and the loss of weight and death of these limpets is attributable to starvation.The lower limit of distribution of C. tramoserica is not due to the direct effects of physical factors associated with prolonged submersion, nor to the impact of predators, but is apparently determined by the presence of rapidly growing, extensive beds of foliose algae at low levels on the shore. The cause of the limit of distribution of S. denticulata is not yet known and predation may prove to be important. Removal of S. denticulata from low-shore algal beds would not, however, affect the domination of substrata by algae. Grazing by S. denticulata at very great density had no effect on algal cover nor weight. In the intertidal community studied, the persistence of a low-shore algal zone, bounded above by abundant grazers is not influenced by the activities of predators, but is a direct result of interactions between the grazers and the algae.

Time resources and laziness in animals.

Abstract: Investigations of time budgets reveal that for many animals a surprising proportion of their active time is spent in inactivity. The question of why these beasts are often idle is investigated by examining their foraging behavior in a model which does not utilize optimization criteria. If an organism's goal is to stay alive, one satisfactory strategy is a thermostat feeding process whereby the animal initiates foraging when it perceives hunger and ceases when it becomes satiated. The simple model is formulated as a Markov chain and analyzed for three cases. Results from each case predict that for many combinations of activity levels and resource spectra, the time spent looking for food is smaller than the time spent not foraging, and laziness may result. Simple decision rules as well as optimization schemes are therefore useful for studying some types of foraging behavior.

Predictions of fate from rosette size in four "biennial" plant species: Verbascum thapsus, Oenothera biennis, Daucus carota, and Tragopogon dubius.

Abstract: Individual plants were marked in field populations of four biennial plant species, Verbascum thapsus L., Oenothera biennis L., Daucus carota L., and Tragopogon dubius Scop., and followed for 2 or 3 years. The relationship of both rosette size and age to the probability of an individual dying, remaining vegetative, or flowering was determined for each species. In all four species, a minimum size must be reached before flowering can be induced and above that minimum the probability of flowering increases directly with rosette size. Conversely, the probability of dying decreases with increasing rosette size. In general, the fate of a rosette appears to be independent of its age although in populations where the probability of death is high for individuals above the minimum size for flowering, the age of a rosette may influence its fate to some extent.

Stomatal closure with soil water depletion not associated with changes in Bulk leaf water status.

Abstract: It has previously been reported that canopy water loss by cowpea (Vigna unguiculata) decreases with small depletions in soil water. In these studies, under field conditions, it was demonstrated that with small changes in soil water status leaf conductance of cowpea decreases in a manner which is consistent with the sensitive regulation of canopy water loss.

Insect defoliation enhances nitrate export from forest ecosystems

Abstract: Chronic defoliation by the fall cankerworm, Alsophila pometaria (Harris), accompanied substantial increases in the stream export of nitrate nitrogen (NO3-N) from three mixed hardwood forests in the southern Appalachians. These integrated results clearly demonstrate a measurable effect of insect consumers on ecosystem processes, and provide support for the regulatory importance of insects on a landscape scale.

Coevolution of pierid butterflies and their cruciferous foodplants : III. Anthocharis cardamines (L.) survival, development and oviposition on different hostplants.

Abstract: The suitability of several Cruciferae species for the survival and development of the larvae of Anthocharis cardamines, which are seed and flower predators, was investigated. Large differences, consistent in time and space, were observed between the survival of sub-populations on different hostplants. Foodplants influenced A. cardamines survival and development by allelochemical and mechanical defences, which may also weaken a larva against pathogen attack. Oviposition by females appeared surprisingly maladaptive however with proportionately most eggs being laid on the hostplants yielding poorest larval survival, in opposition to previous expectations of coevolutionary theory. The evolutionary consequences of butterfly predation for Cruciferae are discussed, and juxtaposed to the needs of pollination.

The effects of light and nitrogen on photosynthesis, leaf characteristics, and dry matter allocation in the chaparral shrub, Diplacus aurantiacus.

Abstract: Plants of Diplacus aurantiacus, a successional shrub common in California chaparral, were grown under controlled conditions in which either quantum flux density or nitrogen availability was varied Photosynthesis and leaf nitrogen content were determined on a leaf area and a leaf weight basis, and whole plant growth was monitored

Contrasts in Energy Intake and Expenditure in Sit-and-Wait and Widely Foraging Lizards

Abstract: Daily energy metabolism and water flux were measured with doubly labeled water in the free-living insectivorous lizards Cnemidophorus tigris (mean body mass 15.7 g) and Callisaurus draconoides (8.6 g) in June 1979 in the Colorado Desert of California. C. tigris was an active forager; it spent 91% of its 5-h daily activity period in movement. C. draconoides was a sit-and-wait predator; it spent less than 2% of its 10-h activity period in movement. C. tigris had significantly higher rates of field energy metabolism and water influx (210 Jg-1 day-1, 36.8 ul H2O g-1 day-1, N=19) than C. draconoides (136, 17.1, N=18). There were no significant differences between the sexes within either species.The extra costs of free existence were calculated from differences between field metabolic rates and maintenance costs estimated from laboratory respirometry. Rates of energy metabolism during the field activity period were about 1.5x resting levels at 40° C (∼field active body temperature) for C. draconoides and 3.3 x resting levels at 40° C (∼field active body temperature) for the more active C. tigris. Feeding rates calculated from water influx data were 13.3 mg g-1 day-1 for C. tigris and 5.8 mg g-1 day-1 for C. draconoides. Though C. tigris had a high rate of energy expenditure, its foraging efficiency [Formula: see text] was higher than C. draconoides'.

Night roosting and the nocturnal time budget of the little brown bat, Myotis lucifugus: Effects of reproductive status, prey density, and environmental conditions.

Abstract: The insectivorous bat Myotis lucifugus typically apportions the night into two foraging periods separated by an interval of night roosting. During this interval, many bats occupy roosts that are used exclusively at night and are spatially separate from maternity roosts. The proportion of the night which bats spend roosting, and thus the proportion spent foraging, vary both daily and seasonally in relation to the reproductive condition of the bats, prey density, and ambient temperature. A single, continuous night roosting period is observed during pregnancy. During lactation, females return to maternity roosts between foraging bouts, and night roosts are used only briefly and sporadically. Maximum use of night roosts occurs in late summer after young become volant. Superimposed upon these seasonal trends is day-to-day variation in the bats' nightly time budget. Long night roosting periods and short foraging periods are associated with cool nights and low prey density. This behavioral response may minimize energetic losses during periods of food scarcity.

Comparisons of δ13C values in leaves of aquatic macrophytes from different habitats in Britain and Finland; some implications for photosynthetic processes in aquatic plants.

Abstract: The δ13C values of submerged aquatic plants from contrasting but relatively defined habitats, and the δ13C values of emergent, floating and submerged leaves of dimorphic aquatic plants, were measured. In many instances the δ13C values of dissolved inorganic carbon in the water were also measured. Plant δ13C values in the vicinity of-40 to-50‰ were found in rapidly flowing spring waters with carbonate δ13C values of-16 to-21‰, consistent with the notion that species such as Fontinalis antipyretica almost exclusively assimilate free CO2 via RuP2 carboxylase. Plant δ13C values in the vicinity of-10 to-15‰ in sluggish water with carbonate δ13C values of about-5‰ were observed, consistent with the notion that boundary layer diffusion and/or HCO3- uptake may determine the δ13C value of submerged aquatic plants in these circumstances. Comparisons of δ13C values of the same or related species growing in waters of similar carbonate δ13C value but different flow rates confirmed this view; more negative δ13C values were frequently associated with plants in fast moving water. In Britain, but not in Finland, the δ13C values of submerged leaves of dimorphic plants were almost invariably more negative than in aerial leaves. The δ13C value of carbonate from chalk streams and in acid springs indicate substantial inputs of respiratory CO2, as opposed to atmospheric carbon. The contributions of these variations in δ13C of the carbon source, and of isotope fractionation in diffusion, to the δ13C value of submerged parts of dimorphic plants is discussed.

Acorn dispersal by the blue jay (Cyanocitta cristata).

Abstract: Blue jays transported and cached 133,000 acorns from a stand of Quercus palustris trees in Blacksburg, Virginia, representing 54% of the total mast crop. A further 20% (49,000) of the mast crop was eaten by jays at the collecting site. A large proportion of the nuts remaining beneath the collecting trees was parasitized by curculionid larvae. The number of nuts transported per caching trip ranged from 1–5 with a mean of 2.2. Mean distance between seed trees and caches was 1.1 km (range: 100 m–1.9 km). Jays appeared to choose species with small- to medium-sized nuts (Quercus palustris, Q. phellos, Q. velutina, Fagus grandifolia) and avoided the larger nuts of Q. borealis and Q. alba. Nuts were cached singly within a few meters of each other and were always covered with debris. Covering may improve germination and early growth by protecting the nut and radicle from desiccation. The vegetation structure of most suburban caching sites was analogous to open, disturbed environments in more natural landscapes. The presence of numerous Quercus seedlings in jay caching sites and the tendency for jays to cache nuts in environments conducive to germination and early growth indicate that blue jays facilitate colonization of members of the Fagaceae.

Field analyses of insect heat budgets: Reflectance, size and heating rates.

Abstract: This paper outlines simple techniques for determining rates of heat gain and loss in relation to the weight and reflectance of insects caught in their natural habitats. In particular the construction of a new 'reflectometer' is described. The results thus obtained permit estimates of the relative importance of size and colour in determining rates of heat exchange and temperature excesses, so allowing better predictions of heat budgets for a given species.

Measures of ecological association.

Abstract: Six criteria suitable for measures of ecological coexistence are proposed. For twenty such measures are examined whether they satisfy these criteria or not. Four of them satisfy all six criteria. Three of them, suggested by Ochiai, Dice and Jaccard are recommended. For them asymptotic standard errors are given. An example is given with asymptotic confidence intervals for the three measures recommended.

Burrow structure and foraging costs in the fossorial rodent, Thomomys bottae

Abstract: A model for calculating the energy cost of burrowing by fossorial rodents is presented and used to examine the energetics of foraging by burrowing. The pocket gopher Thomomys bottae (Rodentia: Geomyidae) digs burrows for access to food. Feeding tunnels of Thomomys are broken into segments by laterals to the surface that are used to dispose of excavated soil. Energy cost of burrowing depends on both soil type and on burrow structure, defined by the length of burrow segments, angle of ascent of laterals, depth of feeding tunnels, and burrow diameter. In a desert scrub habitat, Thomomys adjust burrow segment length to minimize cost of burrowing. Observed segment lengths (mean=1.33 m) closely approximate the minimum-cost segment length of 1.22 m. Minimizing energy expended per meter of tunnel constructed maximizes efficiency of foraging by burrowing in the desert scrub. Burrow diameter and cost of burrowing increase with body size, while benefits do not, so foraging by burrowing becomes less enconomical as body size increases. Maximum possible body size of fossorial mammals depends on habitat productivity and energy cost of burrowing in local soils.

The energetic costs of tail autotomy to reproduction in the lizard Coleonyx brevis (Sauria: Gekkonidae).

Abstract: Energy reserve utilization and energy budgets were compared in tailed and tailless adult female Coleonyx brevis. Carcass, fat body and caudal energy reserves were used for vitellogenesis; mass and energy content (cal/mg and/or cal/reserve) of each were significantly lower at oviposition than at the initiation of vitellogenesis. Total energy reserves accounted for 53% of the reproductive energy investment in tailed females compared to 29% in tailless females. Tailed females had over twice as many reserve calories for egg production than tailless females. Caudal energy reserves represented 60% of the total reserves of tailed females and were one-third greater than the total energy reserves of tailless females. To produce a clutch of eggs both tailed and tailless females supplemented energy reserves with net metabolizable energy that was available after metabolic costs were paid. Tailless females had a significantly greater rate of food ingestion and more net metabolizable energy available for reproduction than tailed females, yet allocated significantly fewer calories/day to reproduction than tailed females, primarily because of the loss of caudal reserves. Reproductive efforts of tailed and tailless females were equivalent. However, the loss of caudal reserves resulted in the production of eggs that were significantly lower in mass and energy content (cal/mg and cal/egg) than when caudal reserves were used. Results empirically support the hypothesis that reproduction has energetic priority over tail regeneration in short-lived, iteroparous species with a low probability of future reproductive success.

Hunting in the kestrel, Falco tinnunculus, and the adaptive significance of daily habits.

Abstract: 1. In an attempt to evaluate the importance of individual daily habits to a freeliving animal, foraging behaviour of kestrels was observed continuously for days in sequence in open country. Data obtained in 2,942 observation hours were used. Flight-hunting was the prominent foraging technique yielding 76% of all prey obtained. 2. Flight-hunting was impeded by rain, fog and wind speeds below 4 m/s and above 12 m/s (Fig. 3). Flight-hunting tended to be suppressed also in response to recent successful strikes and more generally by a high level of post-dawn accumulated prey (Figs. 4, 5). Flight-hunting had a tendency to be enhanced in response to recent unsuccessful strikes (Fig. 6). 3. Trapping results demonstrated a fine-grained daily pattern of common vole trap entries, with peaks at intervals of ca. 2 h (Figs. 7, 8). The interpretation of some of this pattern as representative of vole surface activity was supported by overall strike frequencies of kestrels hunting for voles (Fig. 9). 4. Detailed analysis of the behaviour of three individuals revealed significant peaks in hunting yield and frequency, coinciding with each other and with peaks in vole trapping (Fig. 11). It is suggested that the kestrels adjusted their flight-hunting sessions to times of high 'expected' yield. Vole activity peaks sometimes remained unexploited. 5. Meal frequencies culminated shortly before nightfall except in incubating females. The difference between the daily distributions of hunting and eating was due to some of the prey being cached in daytime and retrieved around dusk (Fig. 13). Caching behaviour is interpreted as a circadian strategy allowing separate optimization of hunting-adjusted to prey availability-and eating-adaptive by retaining minimum body weight in daytime flight and by thermo-regulatory savings at night. 6. Some kestrels showed remarkable constancy from day to day in the temporal distribution of specific behaviours (Fig. 16) and of spatial movements (Figs. 18, 19). In three 1-2 week sequences of observation analysed, flight-hunting frequency peaked 24 h after prey capture (Fig. 17). This is probably based on day to day correlations in flight-hunting frequency as well as on increased motivation for hunting in response to prey capture 24 h ago (Table 5). 7. In one individual with three distinct hunting areas, the tendency to return to an area again was maximal 24 h after prey capture in that area (Fig. 21, Table 6). A field experiment tested the effect of prey capture on the daily distributions of hunting and site choice in this individual (Fig. 22). A significant concentration of flight-hunting activity in the experimental feeding area was observed at the daily time of feeding (Fig. 23). Two alternative hypotheses are compatible with the result. Favoured is the one that the birds use "time memory" for the optimization of their daily patterns of flight-hunting and site choice. 8. By adjusting her daily flight-hunting to times of high yield, one kestrel saved 10-22% on her total time spent flight-hunting. Maximal efficiency, by concentration of all hunting activity in the hour of maximal yield, was not attained, presumably because of information constraints. The generality of the contribution of daily habits to survival is discussed.

Seasonal pattern and energetics of short daily torpor in the Djungarian hamster, Phodopus sungorus.

Abstract: In Phodopus sungorus spontaneous shallow daily torpor occurred only during winter. Frequency of torpor was not affected by low ambient temperature but the seasonal cueing seems primarily dependent on photoperiodic control. Maximum torpor frequency was found in January with 30% of all hamsters living inside or outside being torpid at a time. It is calculated that torpor will reduce long term energy requirements of Phodopus by only 5%. Therefore it is concluded that torpor is not primarily aimed to reduce energy requirements but to guarantee survival of a fraction of a population during short periods of extreme cold load or inaccessability of food.

Leaf absorptances of Mohave and Sonoran desert plants.

Abstract: Leaf absorptances to solar radiation in the 400-700 nm (photosynthetically useful wavelengths) are presented for a diversity of species in the Mohave and Sonoran Deserts of North America. As a life form shrubs are shown to have the widest range of absorptance, with perennial herbs and cacti exhibiting a smaller range, and very little variation in leaf absorptances among trees and annuals. The measurement of leaf absorptance at 625 nm is shown to be the same as the leaf absorptance to solar radiation over the 400-700 nm. Over a wide range of species and absorptances, the total solar leaf absorptance (400-3,000 nm) is shown to be closely related to the 400-700 nm leaf absorptance.