Temperate-zone Species Research Articles

Food Habits and Reproductive Biology of the Endemic Melanesian Elapids: Are Tropical Snakes Really Different?

Do the ecological traits of tropical snakes differ from those of temperate-zone species? We examined preserved specimens in museums to quantify body sizes, sexual dimorphism, dietary habits, and reproductive cycles of the proteroglyphous snake lineages endemic to New Guinea and the Solomon Islands for comparison with previously-studied Australian and Asian species. The Melanesian snakes comprise a diverse group in terms of body sizes (adult sizes from 1 meter), body shapes (slender to heavy- bodied), and behavior (nocturnal to diurnal). Males attain larger sizes than do females in Aspidomorphus and Micropechis, but the reverse is true in Loveridgelaps, Salomonelaps, and Toxicocalamus. Aspido- morphus and Toxicocalamus show significant sex differences in relative head length, but species in the other genera do not. All taxa for which we have data on reproductive mode are oviparous, and produce an average of 3 to 9 large eggs per clutch. Relative to maternal body sizes, Melanesian elapids have significantly smaller clutches than do Australian elapids. The two smaller-bodied genera showed dietary specialisation (on earthworms by Toxicocalamus, and on skinks by Aspidomorphus). Toxicocalamus and the Fijian Ogmodon are thus the only Old World elapids to specialise on invertebrate prey. The larger- bodied taxa (Loveridgelaps, Micropechis, Salomonelaps) have more generalised diets, consisting primarily of lizards and frogs. The distinctive features of the Melanesian elapid fauna (low fecundity in all taxa, and earthworm-eating by Toxicocalamus) may reflect adaptations to tropical habitats, but generalizations about the ecological adaptations of tropical snakes remain elusive.

Thermoregulation of Monitor Lizards in Australia: An Evaluation of Methods in Thermal Biology

The aims of this paper are to compare the thermal ecology of four species of varanid lizards that occupy a range of habitats and climatic regions, and to assess the efficacy of methods for evaluating the extent to which ectothermic animals exploit their thermal environments. Hertz et al. (1993) have proposed several indices of thermoregulation, and these are evaluated with respect to our data from varanid lizards. The thermoregulatory characteristics of three tropical monitor lizards (Varanus panoptes, V. gouldii, and the semiaquatic V. mertensi), and the temperate—zone V. rosenbergi were studied throughout the year. Radiotelemetry was used to measure the body temperatures (Tbs) of free—ranging animals, and microclimatic data were collected to determine the range of possible Tbs that an animal could achieve. Operative temperatures (Tb's) were estimated by biophysical models for each set of animal characteristics and microclimatic conditions. The Tb's selected by animals in a laboratory thermal gradient were used to determine the set—point range of Tb's that the animals voluntarily select. Plots that superimpose Tb's, Tb's, and the set—point range across the day are extremely useful for describing the thermoregulatory characteristics of ectotherms. These plots can be used to determine the extent to which the animals exploit their thermal environment: we define an index of thermal exploitation (Ex) as the time in which Tb's are within the set—point range, divided by the time available for the animal to have its Tb's within the set—point range. Only V. mertensi was active throughout the year. In general, during seasons of inactivity, the Tb's of inactive species fell outside the set—point range, but during periods of activity all species selected Tb's within their set—point range. The temperate—zone species (V. rosenbergi) thermoregulates very carefully during periods when environmental conditions allow the animals to attain the set—point range, and V. gouldii also thermoregulates carefully in the wet season. V. mertensi selects Tb's that are significantly lower than the other species both in the field and in the laboratory, and thermoregulatory indices of this species were intermediate relative to the other species. The amount of time spent in locomotion each day was not correlated with the indices of thermoregulation: the most active species, V. panoptes, was, with respect to several indices, the least careful thermoregulator. The type of question that is being addressed, with respect to the interactions between an animal's thermal environment and its thermoregulatory behavior, determines the appropriateness of the various indices of thermoregulation. The Ex index describes the thermoregulatory characteristics of ecotherms in a heterogeneous thermal environment, and in such an environment a large amount of information can easily be interpreted graphically. This index is less useful in a thermally homogeneous environment.

Tropical Hardwoods Used in Musical Instruments - Can We Substitute them by Temperate Zone Species?

Tropical and some subtropical woods are used for many musical instruments or in parts of them. This paper investigates those physical qualities that are relevant to justifying the application of tropical woods. A substitution by some domestic or Northern American species is only permissible for a few purposes, e.g. for guitar necks or face veneers on piano cabinets. However, it is not appropriate when high hardness and density are needed, or a high Young's modulus together with a small density and a low damping, often combined with a movement as little as possible. Such demands are met best for woodwinds by Grenadille and some different species, for xylophone-bars by a few other species, and for some stringed instrument parts and for bows by special hardwoods only. Some applications of tropical woods are added as a matter of tradition or taste. A substitution by a synthetic material is possible, but usually for secondary instruments only.

Circadian aspect of photoperiodic time measurement in a female house sparrow, Passer domesticus.

Endogenous circadian rhythms are involved in various photoperiodic responses of birds. Investigations involving the mechanisms of photoperiodic time measurement in birds have been confined mainly to temperate zone species using males exclusively. Due to the paucity of experimental evidence on subtropical birds that have very wide distribution, the present study was performed using subtropical female house sparrows. Photoperiodic sparrows were subjected to various T cycles for 60 days in which a fixed 3-h photophase was combined with scotophase in cycles of 20-30 h duration. Simultaneously, two groups of birds were also exposed to short days (light:dark = 8L:16D) or long days (15L:9D) as controls. Significant ovarian growth was found only in cycles of 3L:17D, 3L:23D, 3L:25D, and 3L:27D as well as in 15L:9D, whereas no positive response was detected in 3L:19D, 3L:21D, and 8L:16D. Plasma levels of estradiol showed a close relation to ovarian growth. The results indicate that photoperiodic time measurement in house sparrows involves an endogenous circadian rhythm.

The Effect of Breeding Synchrony On Extra-Pair Mating Systems in Songbirds

Extra-pair mating systems are now considered to be typical of songbirds because DNA fingerprinting has revealed high rates of extra-pair fertilizations (EPFs) in so many species previously thought to be monogamous. However, there is no general framework to explain the tremendous variability among songbirds in EPF rate. Here, in a comparison of EPF rates and temporal patterns of nesting among songbirds, we show that EPFs are most common in species where females breed synchronously. We argue that for both males and females, a temporal concentration of female fertility (breeding synchrony) increases the net benefits of seeking EPFs. One implication of this finding is that tropical songbirds, most of which breed asynchronously, are predicted to have low levels of extra-pair matings. Testes size is positively correlated with frequency of EPFs, and as predicted, tropical songbirds had small testes size relative to temperate zone species. The few DNA fingerprinting studies that exist for socially monogamous tropical songbirds support the correlation between breeding synchrony and EPFs. We believe that breeding synchrony is the most important factor promoting the evolution of extra-pair mating systems.

Systemic Diseases on Hosts with Different Growth Patterns

To date, several reviews and books have focused on fungal pathogens in natural plant populations (Burdon 1987, Augspurger 1988, Alexander 1990). All stress the importance of fungal pathogens in shaping plant populations, since they have the potential to cause high mortality in adult plants (Paul and Ayres 1986), seedlings (Augspurger 1984) and seeds (Hendrix and Campbell 1973). Despite the awareness of the importance of pathogens, we still know very little about the general nature of host-pathogen interactions in natural populations. At present, we have no good way of predicting the immediate outcome of any interaction between a given fungus and its host plant, i.e. the effects of pathogens on the survival, biomass, and reproduction of individual hosts. Not surprisingly then, we cannot predict the likely long-term consequences of a given interaction at the population level. One reason why predictions about host-pathogen systems are few, may be a consequence of treating pathogens as if they belong to a single homogeneous group (but see Burdon 1991, 1993). However, a large number of fungal genera and families are known to include pathogenic species. Studying them closely reveals that elements of life history strategies, such as longevity, reproduction, host specificity and growth pattern, vary considerably between species of pathogens. One important life history trait is whether the fungus is non-systemic or systemic. The former group consists of fungal pathogens that are not able to grow away from the site of infection, while the latter group consists of those pathogens that are able grow internally from the site of infection to other parts of the plant, and may produce pustules along the way. Many species of rusts and smuts are systemic and important pathogens of herbs, grasses and trees (Wilson and Henderson 1966, Lindeberg 1959). Systemic fungal diseases often form a perennial mycelium within the plant. They often form confluent pustules that strongly deform the diseased part, e.g. stems can be severely twisted (Parker 1987, Wennstrdm and Ericson 1992). Disease symptoms may be seen on the entire plant (Bryzgalova 1928), but more commonly, pustules are only seen on specific parts of the plants such as leaves (e.g. Puccinia pulsatillae on Pulsatilla pratensis, Wennstrbm and Ericson 1991) or flowers (e.g. Microbotryum (Ustilago) violaceum on Silene dioica, Carlsson and Elmqvist 1992). The extent of damage caused to the host plants varies considerably between systemic diseases. For example, the systemic Puccinia pulsatillae enhances growth and increases survival of its host, Pulsatilla pratensis (Wennstrom and Ericson 1991), while the systemic Urocystis trientalis reduces survival and growth of its host, Trientalis europaea (Wennstrom and Ericson 1990). One way to understand and hopefully also develop a predictive theory of how fungal pathogens behave in plant populations and communities is to incorporate studies of the life-history of the pathogen (cf. Andrews and Rouse 1982). Life history studies should, however, also include the life-history strategies of the host, e.g. host longevity, reproduction and growth pattern. The growth pattern, and especially variation in the lateral growth of the host, may prove to be important in host-pathogen interactions, as incomplete transmission of systemic diseases has been reported for host plants with a strong lateral growth (e.g. Pady 1939, van den Ende et al. 1987, Wennstr6m and Ericson 1992). Although about 70% of all plant species in temperate zones of the world are clonal, the exact growth pattern varies considerably from species to species (van Groenendael and de Kroon 1990). For example, ramets can be formed close to the parent (hereafter called plants with weak lateral growth) or on lateral shoots or roots at some distance from the parent (hereafter called plants with a strong lateral growth). In this paper, I concentrate on perennial systemic rusts and smuts on host plants with different growth patterns. I compare characteristics of disease expression (disease levels, infection rate), and host response between hosts with weak lateral growth, and those with strong lateral growth.

Reproduction and Lipid Utilization of Tropical Populations of Sceloporus variabilis

Reproductive characteristics and lipid cycles of two tropical populations of the insectivorous lizard Sceloporus variabilis inhabiting different elevations were compared. Compared to phylogenetically related temperate zone species, S. variabilis demonstrates reproductive characteristics predicted in the literature for lizards inhabiting relatively aseasonal environments: small clutch size (4.3-4.6) relative to body size (60-61 mm SVL), highest clutch frequency (4.5-6), earliest age at maturity (4-7 months), longest reproductive season (8-9.5 months) and smaller relative clutch mass (0.203-0.212). Most of these trends are also found in the comparison of lizards from the high elevation population (1000 m above sea level), where seasonality is more conspicuous, with lizards from the low elevation population (45 m above sea level) where the environment is more equable. At low elevation, the reproductive season is longer, permitting reproductive potential to be higher. In addition, incubation time of eggs is shorter at low elevation and thus, some females are able to reproduce at the end of the same reproductive season in which they were born. Seasonal shifts in egg size in the high elevation population are analyzed regarding the bet-hedging and the parental investment models. Lizards at both elevations store lipids in fat bodies and in body tissues that are used at the beginning of the reproductive season. Higher and more suitable ambient temperature and abundant food later in the reproductive season allow lizards to get the energy necessary for reproduction directly from the environment, until the nortes (northern storms) season restricts lizard activity. Juveniles use all energy from food for growth and do not store lipids until shortly before reaching maturity.

Sensitivity of Syrian hamsters (Mesocricetus auratus) to amplitudes and rates of photoperiodic change typical of the tropics.

Empirical data suggest that reproductive photoresponsiveness occurs in some populations of mammals above 13 degrees of latitude, but may be absent in populations from 0 degrees to 10 degrees of latitude. The present experiments examined the degree to which the low amplitude of change in photoperiod in the tropics constrains mammals from using daylength as a seasonal cue. The Syrian hamster, a temperate-zone species, was studied because of its well-documented ability to respond to small changes in photoperiod, and because of the absence of an alternative robustly responding species from the tropics. We subjected adult male hamsters to photoperiods that mimicked the amplitude and rate of photoperiod change of 30 degrees, 20 degrees, 10 degrees, and 5 degrees of latitude, but centered around an estimate of their critical daylength. For comparison, a fifth group was subjected to an abrupt change in daylength of a magnitude equal to the total annual variation occurring at 30 degrees. The two groups experiencing the gradually changing daylengths of 30 degrees and 20 degrees showed less within-group synchrony during testicular regression; in other dimensions of the annual testis cycle, including the degree of synchrony exhibited during recrudescence, they reacted similarly to the hamsters given the abrupt change in daylength. Some of the hamsters exposed to the gradually changing daylengths of 10 degrees responded to this challenge, as did a few in the 5 degrees treatment--in both cases, with poor within-group synchrony and a submaximal decrease in testis size. In an abbreviated second experiment, hamsters given abrupt decreases in daylength of magnitudes equal to those of the 10 degrees and 5 degrees groups responded slightly more frequently, and with maximal decreases in testis size. This suggests that mammals may not be constrained absolutely by an inability to respond to changes in photoperiod at 5 degrees to 10 degrees latitude. Seasonally breeding populations of mammals in the deep tropics that do not use photoperiod to regulate reproduction may use nonphotoperiodic cues because they offer a higher signal-to-noise ratio than do tropical changes in photoperiod.

Modeling Load‐Slip Behavior of Nailed Joints

A commonly used mathematical model to predict the lateral load‐slip (P‐Δ) behavior of nailed joints in wood is expanded in this study to account for several important characteristics of the connection. Nonlinear curve‐fitting procedures are used to develop prediction relationships for parameters A and B in equation (P=Alog10[1+BΔ]) for a variety of joint material and geometric characteristics. P‐Δ curves are experimentally obtained for 292 single‐shear nailed joints made with main and side members consisting of seven hardwoods indigenous to the Amazonian region of Brazil, four diameters of common wire nails (2.87, 3.33, 3.76, and 4.07 mm), three nominal moisture contents (6, 12, and 18%), and six nominal side‐member thicknesses (12, 19, 25, 31, 38, and 50 mm). The specific gravity (oven‐dry volume basis) of individual specimens ranges from 0.36 to 0.85. This range is larger than would be found among temperate zone species customarily used in construction. A contemporary statistical software package is used to perform regression analyses to predict A and B from 33 functions of various combinations of the nail diameter, side‐member thickness, and main‐ and side‐member specific gravity. Results indicate that the best prediction equation models the shape of the experimental curves with reasonable accuracy. When the estimated parameters are used to predict the P‐Δ curves for the 292 test joints, an average mean deviation of about -11% was found. The negative value suggests that the model tended to overpredict joint stiffness.

The Hormonal Control of Territorial Aggression in Tropical Birds

Investigations of the hormonal control of avian territorial aggression have focused on temperate zone species where typically only males sing and defend territories in the breeding season, and have implicated testosterone in the control of these behaviors. However, most avian species are tropical and in many such species both sexes sing and defend year-round territories. We have examined the mechanisms underlying territoriality in the White-browed Sparrow Weaver Plocepasser mahali, in Zambia, and the Bay Wren Thryothorus nigricapillus, in Panama. In both species, we found low circulating levels of steroid hormones and no evidence for the regulation of territorial aggression by testosterone even in the breeding season. However, there were preliminary indications of a role for luteinizing hormone in maintaining territorial aggression. Thus, in contrast to temperate zone species, territorial aggression in these two tropical species is either independent of control by steroid hormones or is mediated by a non-gonadal hormone. These results, and the few data from other tropical species, suggest that the general assumption that androgens maintain territorial aggression may apply only to temperate species.

Reproductive Biology and Diets of Goannas (Reptilia: Varanidae) from Australia

Aspects of the reproductive biology and diets of nine species of Varanus from the seasonal tropics and temperate zones of Australia were examined by dissection of 386 preserved museum specimens. We investigated whether morphological and habitat diversity in the varanids was expressed in reproductive and dietary diversity. Most species from seasonal tropical areas had enlarged testes in the dry season (June-October) and females with oviductal eggs were collected at the end of the dry season and the beginning of the wet season (September-January). However, three species seemed to be exceptions to this trend, with an extended reproductive season (V. storr), or reproductive activity in the late wet season (V. semiremex and V. kingorum). A diversity of reproductive seasons for varanids from seasonal tropical regions in Australia was also found in a review of the literature. Temperate zone species had enlarged testes in spring (September-November) and laid eggs in spring or late summer. Clutch sizes ranged from 1-7 eggs. Regression slopes of maternal SVL and clutch size seemed to be higher for the smaller-bodied species compared to the larger-bodied species, but sample sizes were too low to compare them statistically. A review of reproductive data on Australian varanids suggested that some large-bodied species (e.g., V. varius) had relatively small clutch sizes. Most species had generalized diets with lizards and orthopterans being the most important prey. Large-bodied species such as V. giganteus and V. glebopalma tended to eat larger prey items, and specialized on vertebrate prey. Varanus semiremex ate mostly aquatic prey. Diets were relatively similar for most species but appear to be influenced by body size and habitat.

Load-Slip Behavior of Nailed Joints in Seven Amazonian Hardwoods

Abstract Two hundred ninety-two nailed joints in seven species of Amazonian hardwoods were tested to evaluate their load-slip (P-Δ) behavior when subjected to lateral loading. The seven species commonly used in Brazilian light-frame construction had a range of specific gravities from 0.36 to 0.85 (based on an oven-dry volume) Four sizes of common wire nails were used to construct joints with main and side members of the same species. From these tests, embedding strength values associated with a 5% offset load were obtained from the experimental (P-Δ) curves and equations derived from the European Yield Theory. The results suggest that the behavior of nailed joints made with tropical hardwoods is similar to that found in temperate zone species. Wood moisture content, in the range studied, did not meaningfully affect joint P-Δ behavior. In addition, embedding strength was influenced by the specific gravity of the connected material. However, no species effect was observable between species of similar specific gravity. Finally, an effect of nail diameter on embedding strength was seen; however, the lack of homogeneity of test materials precluded the accurate prediction of this effect. Since the embedding strength data demonstrated some degree of positive skewness, three commonly used statistical distributions (log-normal, three-parameter Weibull, and Johnson's SB) were evaluated to quantify the variability of this parameter. All three distributions were excellent descriptors of behavior. Therefore any of these mathematical models would be a rational choice for representing embedding strength.

Population Structure of Temperate Zone Insectivorous Bats in Relation to Foraging Behaviour and Energy Demand

(1) The morphology, echolocation calls, foraging behaviour and prey distribution of two temperate zone species of insectivorous bats was studied to assess the hypothesis that sexual differences in distribution pattern are the result of differences in energy demand. (2) In an area of the eastern slopes of the Rocky Mountains (Canada) characterized by low ambient temperatures and low insect abundance, over 90%yo of the Myotis lucifugus caught during the summer were adult males while an equal sex ratio of Myotis evotis was caught. (3) M. lucifugus forage low over water on aerial prey, especially chironomids, which are abundant only for a short time after sunset. (4) M. evotis forage along paths and in forest and prey primarily on moths. They take insects from the air but laboratory studies indicate that they are also adept at gleaning prey from the ground and vegetation. This provides a broader, more predictable food resource than is available to M. lucifugus. (5) I suggest that the flexible foraging strategy of M. evotis allows reproductive females, with their high energy demand, to inhabit areas that cannot support reproductive female M. lucifugus. Males of both species can exist in such areas because of lower energy demand and, potentially, the use of torpor under adverse conditions. Selecting such areas and reducing foraging time may benefit males if there are risks incurred while they forage.

The Effect of Position on Fruit Characteristics, and Relationships Among Components of Yield in Phytolacca rivinoides (Phytolaccaceae)

We examined position effects on components of fruit mass within infructescences of Phytolacca rivinoides to determine whether distal portions of an infructescence provide fewer resources for developing fruits than basal portions, resulting in a decrease in fruit or seed mass, or seed number per fruit towards the distal end of a raceme. We also sought evidence for yield compensation due to resource limitation by measuring the relationships between reproductive components among individual fruits and among infructescence means. The results of three natural experiments did not show that distal portions of a raceme are consistently at a disadvantage with regard to maternal resources; different fruit characteristics showed different patterns. In general, there were significant dedines in total fruit mass and pulp mass from the basal to the distal portions of an infructescence. In contrast, total seed mass, mean individual seed mass, and seed number per fruit showed no significant decline; in some cases these parameters increased distally. In two natural experiments, we controlled for developmental effects on fruit, pulp and seed mass by comparing only fully ripened fruits located at relatively basal and distal positions. The results of these two experiments differed markedly. In one experiment, total seed mass per fruit and mean individual seed mass per fruit increased significantly towards the distal end of the sampled infructescences, while seed number per fruit remained unchanged. In the other experiment, total seed mass and mean individual seed mass per fruit remained constant, while seed number per fruit increased significantly towards distal positions of the infructescences. The relationship between seed mass and seed number per fruit was explored in three ways, but none revealed evidence for maternal resource limitation leading to an inverse relationship (or trade-off) between mass and number. First, a regression of mean seed mass on seed number per fruit indicated that the two traits are independent of each other (N = a total of 500 fruits on 25 infructescences). Second, regressions of mean individual seed mass on seed number among fruits within each of 25 infructescences showed no evidence that seed mass was negatively associated with seed number; in two infructescences, mean individual seed mass and seed number per fruit were positively associated. Finally, among infructescences, mean individual seed mass was independent of mean seed number per fruit. Infructescence length was positively correlated with fruit number but independent of all other measured parameters, indicating that infructescences bearing many fruits did not produce fewer or smaller seeds than those with few fruits. The most surprising outcomes of this study are that we detected no strong position effects on, or inverse relationships between, seed mass and number that indicate that the availability of resources determines seed mass or number per fruit, though this is a phenomenon seen widely within temperate zone species.

Habitat selection by the queens of the leaf-cutting ant Atta sexdens L. in Brazil

The founding of a new nest is the most crucial period in the life of an ant colony (Wilson 1971). Mechanisms that enhance colony survivorship during this phase are thus of great value. Of special importance is the search for a suitable habitat by the foundress queen, since established colonies of most ant species are unable to migrate over long distances (Wilson & Hunt 1966). That ant queens select the habitat in which they will found a new colony has been demonstrated for several temperate zone species (Brian 1952, Brian et al. 1966, Pontin 1960, Wilson & Hunt 1966) and for the Neotropical leaf-cutting ants Atta cephalotes L. and Acromyrmex octospinosus Reich (Cherrett 1968). In this paper, evidence that such a mechanism is operating among the foundress queens of another leaf-cutting ant species, Atta sexdens L., is presented. Furthermore, it is shown that, once in the preferred habitat, they search for the best microhabitat. Field work was done at 'Fazenda Dimona', a ranch located about 70 km north of Manaus, Brazil (600 4' W, 20 19 S). In this ranch two forest fragments of 1 ha, one of 10 ha and one of 100 ha were created during late 1984 to meet the requirements of the Minimum Critical Size of Ecosystem Project (a collaborative binational research project between the Instituto Nacional de Pesquisas da Amazonia and the World Wildlife Fund-US). A fifth fragment about 100 m wide and bordering a local stream, but not related to the MCSE Project, was created at the same time. Brachiaria grass was planted in the cleared area, but no efforts were made to maintain the pasture free of weed species. One year later, at the beginning of the study, stands of secondary vegetation 1-2 m tall, mainly Laetia procera (Poepp.) Eichl., Solanum rugosum Dun. and species of Cecropia, were present throughout the pasture. The vegetation of the fragments was a primary, terra-firme forest (as defined by Guillaumet 1987).

Thermoregulation and Activity Patterns of the Sand Wasp Steniolia longirostra (Say) (Hymenoptera: Sphecidae) in Costa Rica

In the neotropical sand wasp Steniolia longirostr-a (Say), female activity levels in the nesting area were negatively correlated to ambient temperature and positively correlated to relative air humidity. The wasps showed high activity below 350C and above 40 percent relative humidity. Females with a low wing load had a lower body temperature during flight compared to females with a high wing load. This may offer females with favorable body proportions benefits, as they can enjoy longer daily provisioning periods. MICROCLIMATE HAS A SUBSTANTIAL EFFECT on the behavior of most insect species. Maintenance of an adequate body temperature and water balance is difficult for small animals, whether using ectothermic (behavioral) or endothermic (physiological) mechanisms for its regulation (May 1985). Numerous studies of thermoregulation in Hymenoptera have been carried out in recent years. However, as in other insect groups, most research has been conducted on temperate zone species (but see May & Casey 1983, Vogt & Heinrich 1987). Sand or digger wasps occupy dry and sunny habitats in temperate and tropical areas. Many species dig their burrows in the ground, exposing themselves to extreme shifts in ambient temperature during surface activities (Nielsen 1945). The few studies published on their thermoregulation suggest that they are ectothermic, that is, regulate their body temperature by behavioral means (Willmer 1985a, O'Neill & O'Neill 1988). One should suspect intraspecific variation in body size of ground-nesting tropical wasps to be related to their thermoand hygroregulatory capacity (as for temperate species, see Wilmer 1985 a). As a consequence, I hypothesized differences in activity patterns between differently sized nesting females. I present here some data on the activity and thermoregulation of a gregarious neotropical sand wasp, Steniolia longirostra (Say) (Hymenoptera: Sphecidae: Nyssoninae), during the hot and dry season in Costa Rica. This genus embraces about fifteen species, ranging from southwestern Canada to Central America. S. longirostra has been recorded from late September through May, mainly from southern Mexico. The females of this medium-sized wasp are characterized by their fast, hovering flight. They dig burrows in dry, sandy ground, where they provision their larvae with flies (Evans & Gillaspy 1964, Gillaspy 1964).

Population Ecology of the Cooperatively Breeding Acorn Woodpecker

Ever since the acorn woodpecker was observed and described by Spanish explorers, its behavior--particularly the unique habit of caching acorns in specialized storage trees or granaries--has impressed observers. Acorn woodpeckers are also one of the few temperate zone species in which young are reared communally in family groups. This demographic study investigates the complexities of acorn storage and group living in acorn woodpeckers at Hastings Reservation in central coastal California. It is one of the most thorough studies of any avian social system to date.

Thermal Relations of Some Tropical Frogs Along an Altitudinal Gradient

Temperate-zone amphibians generally show an acclimation response of tolerance to high temperatures (CTMax), and several wideranging species have been found to have a negative correlation between elevation and CTMax. Fewer tropical species have been examined, but Heatwole et al. (1965) reported that the Puerto Rican frog Eleutherodactylusportoricensis failed to show an acclimation response, but did show a negative correlation between elevation and CTMax. Subsequently, E. portoricensis, as originally understood, was found to consist of a widespread species (Eleutherodactylus coqui) and a species restricted to high elevations (E. portoricensis) (Thomas 1965). CTMax was determined for these two species, and we found that differences previously believed to be attributable to elevation are, in fact, interspecific differences. There were no differences in CTMax of E. coqui from different elevations, but E. portoricensis had significantly lower CTMax. E. coqui failed to show an acclimation response. The few species of tropical amphibians that have been investigated suggest that, unlike most temperate-zone species, some tropical species fail to show an acclimation response, and some fail to show a negative correlation between CTMax and elevation. ANIMALS CAN RESPOND to environmental change by behavioral adjustments (fast response), physiological adjustments such as acclimatization (slower response), or over a longer time, by evolutionary adjustments such as structural and enzymatic changes (Hertz 1981). The relative degree to which animals respond to environmental change at any of these three levels can be qualitatively described by the term plasticity. In this paper we will discuss responses to thermal environments in terms of both physiological plasticity, the ability to acclimate, and evolutionary plasticity, the ability of populations to adjust to local conditions via selection. These two levels of response are not independent because the ability to make physiological adjustments is undoubtedly genetically controlled and is therefore subject to evolutionary change. Given the differences in the thermal regimes of temperate and tropical regions, a better understanding of the physiological plasticity and evolutionary plasticity of organisms is important to our understanding of the evolution of tropical and temperatezone species. Correlation between critical thermal maxima (CTMax) and environmental temperatures suggest that tolerances to high temperatures reflect adaptations of populations to their local thermal environments (Snyder & Weathers 1975, Miller & Packard 1977, Howard et al. 1983). Thus, tropical species tend to have higher CTMax than temperate species (Brattstrom 1968, 1970; Snyder & Weathers 1975). Brattstrom (1968, 1970) found, in general, no difference between temperate and tropical species in their ability to adjust their tolerances to high temperatures (CTMax) by acclimation. However, acclimation temperature does not alter the standard metabolic rates of most tropical amphibians, whereas all temperate-zone amphibians that have been tested show significant acclimation of metabolism (Feder 1978, 1982). For amphibians in temperate regions, individuals from cool areas at high elevation have lower CTMax than conspecifics from lower, warmer sites (Brattstrom 1968 provides an example and an apparent exception; Cupp & Brodie 1972, Miller & Packard 1977, Hoppe 1978, Howard et al. 1983, Delson & Whitford 1973 demonstrated this trend, but only in neotenic individuals). Fewer tropical species have been examined along an elevational transect, but Heatwole et al. (1965) reported that Eleutherodactylus portoricensis from Puerto Rico showed a trend in temperature tolerance similar to that of the temperate species mentioned above, with individuals from high elevations having lower CTMax than individuals from low elevation. However, the tadpoles of another Puerto Rican species (Leptodactylus albilabris) did not show a relationship between elevation and CTMax (Heatwole et al. 1968). Subsequent to the study of Heatwole et al. (1965), E. portoricensis, as then understood, was found to consist of two species that differ in subtle morphological and vocal characters: Eleutherodactylus coqui, widespread throughout Puerto Rico, and E. portoricensis, restricted to high elevations (Thomas 1965). This raised the possibility that the sample of frogs collected by Heatwole et al. (1965) from the high elevation site may have consisted of either E. portoricensis, E. coqui, or a mixture of the two. We reexamined the CTMax of these Puerto Rican frogs to look for interspecific differences and to compare E. coqui from high and low elevations. In addition, we measured the critical thermal minima (CTMin) of the three groups I Received 19 November 1985, revision received 29 November 1986, accepted 15 December 1986. 2 Present address: University College of the Northern Territory, GPO Box 1341, Darwin, NT 0801, Australia. 236 BIOTROPICA 20(3): 236-239 1988 This content downloaded from 157.55.39.120 on Mon, 05 Sep 2016 06:09:18 UTC All use subject to http://about.jstor.org/terms of frogs, and E. coqui were acclimated at 20 and 27?C to determine if the CTMax of these frogs were affected by acclimation. To confirm the results of the experiment (performed in April 1984), the CTMax experiment was repeated in late October 1984 on frogs that were tested within 4 hr of capture.

Pulp composition and the invasion and decay of fruits by microbes

Among temperate-zone plant species, fruits with fat-rich pulp have been predicted to disappear more rapidly than low-fat fruits, in part because of more rapid decay by microbes. The influence of fat content of pulp on the susceptibility of fruits to microbial invasion and the rate of pulp deterioration after invasion were examined using Cornus amomum fruits (approximately 5.8% crude fat) and C. racemosa fruits (approximately 23.1% crude fat). Fruits were surface sterilized, punctured with a sterile needle or left undamaged, and inoculated with sterile water, a suspension of bacteria, or a suspension of fungal spores. The two species did not differ significantly in the number of days to first deterioration (= susceptibility), but whole C amomum fruits deteriorated faster than did whole C. racemosa fruits after invasion was first visible. This difference between species persisted when the difference in mean dry pulp mass was taken into account using an exponential model of pulp decay. The two Cornus species did not differ in rate of pulp deterioration (milligrams dry tissue per day) when a linear model of microbial decay of pulp was used. In these two species, higher fat content of pulp does not yield greater susceptibility to invasion or higher rate of deterioration by microbes.

The spatial precision of the honey bees' dance communication

Many social insect species that employ directional recruitment to food finds communicate the location of their targets with seemingly needless imprecision. Here we present evidence that the spatial precision of the honey bees' dance communication has been “tuned” by selection so that recruits are neither so accurate that they usually find areas which have already been depleted nor so inaccurate that they usually fail to find the advertised resources altogether. First, the bees' distance errors are similar in magnitude to their directional errors, and their angular errors decrease greatly with increasing distance to the target (decreasing more than fourfold between 100 and 700 m). As a result, the absolute scatter of recruits remains relatively constant with changing distance to the target (increasing by less than 50% between 100 and 700 m). This is to be expected if the optimal level of imprecision is the same for distance and direction and does not change with the distance of the target from the nest. Second, comparative studies involving three tropical- and one temperate-zone species (all Apis)suggest that the precision of the bees' languages may have been tuned in accordance with the spatial characteristics of the resources each species uses. We suggest that both the round dance, which conveys no directional information for nearby targets, and the high angular divergence in waggle dances indicating targets within several hundred meters of the colony are both understandable in this context.