Litter Arthropods Research Articles

Effect of sewage effluent on soil fauna in a Pinus-radiata plantation

Water and nutrients in effluent applied to land may influence soil processes. This study uses late summer and autumn samples to assess changes in litter and soil fauna under a 17-year-old Pinus radiata plantation on dune sands of the Waitarere-Hokio association after 7 years of spray irrigation of sewage effluent. Populations estimated included 12 groups of litter arthoropods, earthworms, enchytraeids, tardigrades, rotifers and nematodes. Three groups of litter arthropods (adult diptera, spiders and aphids) were significantly less abundant in the effluent-treated area than in the unirrigated control. Increased moisture content was apparently responsible for greatly increased populations of earthworms and nematodes in the effluent-treated area. Bacterial-feeding and predatory nematodes showed marked increases, while fungal-feeding nematodes declined significantly. The nematode maturity index (MI) was lower in all treated plots. After effluent had been withheld for 52 days, there were significant increases in isopods and Collembola. Rotifers were most abundant in the control area. It appears that effluent enhanced physical breakdown of the P. radiata litter. Movement of the decayed fragments into the upper layers of sand may have produced conditions unfavourable for enchytraeids and rotifers.

A Hierarchical Model for Decomposition in Terrestrial Ecosystems: Application to Soils of the Humid Tropics

A general model is presented in which the dynamics of decomposition in terrestrial ecosystems are determined by a set of hierarchically organized factors which regulate microbial activity at decreasing scales of time and space in the following order: climate - clay mineralogy + nutrient status of soil - quality of decomposing resources - effect of macroorganisms (i.e., roots and invertebrates). At the lower scale of determination, biological systems of regulation based on mutualistic relationships between macro- and microorganisms ultimately determine the rates and pathways of decomposition. Four such systems are defined, i.e., the litter and surface roots system, the rhizosphere, the drilosphere and the termitosphere in which the regulating macroorganisms are respectively litter arthropods and surface roots, live subterranean roots, endogeic earthworms, and termites. In the humid tropics, this general model is often altered because climatic and edaphic constraints are in many cases not important and because high temperature and moisture conditions greatly enhance the activity of mutualistic biological systems of regulation which exert a much stronger control on litter and soil organic matter dynamics. This general hypothesis is considered in the light of available information from tropical rain forests and humid savannas. Theoretical and practical implications regarding the biodiversity issue and management practices are further discussed. It is concluded that biodiversity is probably determined, at least partly, by soil biological processes as a consequence of enhanced mutualistic interactions, which enlarge the resource base available to plants. It is also concluded that any effort to restore or rehabilitate degraded soils in the humid tropics is promised to fail unless optimum levels of root and invertebrate activities are promoted and the resulting regulation effects operate in the four abovedescribed biological systems of regulation. Research required to substantiate and adequately test the present set of concepts and hypotheses are expressed.

Responses of litter arthropods to major natural or artificial ecological disturbances in mountain ash forest

AbstractPitfall trapping was used in commercial Mountain Ash (Eucalyptus regnans) regrowth forest to study the effects on epigeal arthropods of high‐intensity wildfire plus salvage logging, and of harvesting by clearfelling plus slash burning, followed by fire‐induced natural or artificially established regeneration respectively. The study, the first of its kind in the Victorian Central Highlands, 60 km east of Melbourne, was based on 146 922 specimens of 30 ordinal or lower level taxa collected over a 3‐year period. The abrupt replacement of the ecologically complex regrowth forest by ecologically much simpler even‐aged regeneration caused appreciable instability among the litter‐frequenting arthropods. An immediate decline in diversity occurred due to short‐term boosts in activity of some common ‘major’ taxa (notably a species of seed‐harvesting ant) and the suppression of other taxa. A broad mix of functionally diverse taxa reappeared within two years of regeneration, and all but three rarely trapped ‘minor’ taxa present in undisturbed 43–46 year old regrowth (‘control’) forest had returned within 5 years. Epigeal arthropods therefore appeared to be affected only over a short period relative to the nominal 80–150 year rotation of the E. regnans ecosystem. Research is needed at the species level to achieve a more precise assessment of arthropod responses to major ecological disturbances.

Seasonal variation in concentration of cadmium in litter arthropods from a metal contaminated site

Seasonal variation in concentration of cadmium in litter arthropods from a metal contaminated site

HABITAT OF A NEW MYMAROMMATIDAE FOUND IN SOUTHERN QUEBEC, CANADA (HYMENOPTERA: TEREBRANTES)

During a study on the litter arthropods of the natural forests of southern Quebec, Mymarommatidae specimens were found near Lachute, northwest of Montreal. Fewer than 200 specimens of Mymarommatidae have been collected throughout the world (Huber 1987); there are only nine species, all in the genus Palaeomymar Meunier (Yoshimoto 1984). Morphologically, the insects are characterized by a two-segmented abdominal petiole and atrophied posterior wings attached to the anal margin of entirely reticulated anterior wings (Huber 1987). Their biology is still unknown (J.T. Huber, pers. comm.), although it is thought that they may be insect egg parasites (Yoshimoto 1984). Yoshimoto (1984) included the Mymarommatidae in the Chalcidoidea. However, Gibson (1986) proposed not to include them in a superfamily until the phyletic relationships of the Terebrantes are better defined.

Food Supplementation in a Tropical Mainland Anole, Norops Humilis: Demographic Effects

The concept of food limitation has played a key role in the theoretical framework of population and community ecology, especially for anoline lizards. A common hypothesis is that food is limited for island anoles but is relatively unlimited for mainland anoles. In this study I manipulated prey availability of investigate how food affects population parameters for Norops humilis at a site in the Atlantic lowland wet forest of Costa Rica. Mark—recapture data were collected on control and experimental plots over a 9—mo pretest and 7—mo test period during which 9910 observations were made on 1582 individuals. Manipulation (increase) of food resulted in an approximate doubling of population density. Significant increases in the numbers of hatchlings, immigrants, and survivors resulted in increased numbers of juveniles. However, I observed no increase in the numbers of juveniles recruited to adulthood. Instead, losses of juveniles due to death and emigration were significantly increased. The juveniles population represented a "doomed surplus" that had little direct effect on increasing the size of the reproductive population int he presence of extra food. The density of adult males and females increased survival and immigration. Population density increased proportionally more for adult females than for males and for juveniles than for adults. Increased female population density resulted in a significant increase in the number of eggs laid. Loss (mortality plus emigration) of adults was not affected by supplemental feeding. As the increased number of juveniles did not increase the number of adults recruited from these juveniles, must have increased in severity on experimental plots. These effects of food on N. humilis demography suggest a conceptual model for cycles of abundance of this species and other predators of arthropods within the leaf litter of primary wet forest. The cyclic increase in arthropod food resources later in the dry season appears to be triggered by leaf drop of forest trees, which in turn triggers demographic responses in predators of leaf—litter arthropods, such as N. humilis.

Importance of Body-Size for Cadmium Accumulation By Forest Litter Arthropods

To determine the role of soil arthropods in the cycling of cadmium, the influence of body weight on cadmium accumulation was studied using nine species of arthropods sampled for four seasons from a metal contaminated forest soil. The relationship between weight and body burden was described by a power function, the parameters of which were estimated by functional regression methods according to Ricker. A clear relationship between weight and cadmium burden has been found in 26 out of 39 samples. The slopes of the regression lines varied between 0.57 and 5.97. Variation within a species occurred throughout the year, but the differences were significant in a few cases only. Age, growth and activity appear to be the main factors determining seasonal variation in slope coefficient. Slopes calculated for single life stages appeared to be steeper than slopes calculated for the whole population. This phenomenon may be attributed to the ability of species to loose cadmium between the life stages. The analysis shows that the relationship between body-size and cadmium level cannot be interpreted as a simple accumulation phenomenon, since there are opposite effects of age, weight and season. These factors must be taken into account when calculating the annual flow of cadmium through a soil arthropod community.

Effect of Increased Soil Moisture and Reduced Soil Temperature on a Desert Soil Arthropod Community

The effects of soil moisture and temperature on arthropod communities were experimentally examined in the northern Chihuahuan Desert of New Mexico. Shaded plots were established which lowered the soil temperature several degrees; some plots received artificial rainfall to increase soil moisture. Shading reduced soil temperature at 5-cm depth 7-10 C. Soil moisture at 5 cm accounted for most of the variation in surface activity of subterranean termites (r values between 0.3 and 0.7). Termites did not respond to temperature differences. When all soils were at field capacity, there was no difference in termite activity in shaded and unshaded plots. There were higher densities of microarthropods in litter bags on the shaded plots than on the unshaded plots. Numbers of microarthropods were an order of magnitude larger in litter bags on watered and shaded plots than on other plots. Lower litter temperatures apparently affect litter arthropods more than increased soil moisture. Shade had no effect on ant colonies but there were fewer colonies on the watered plots. There was between 40 to 50% mass loss from creosotebush leaf litter after 7 months on all plots. Water and soil temperature had no effect on decomposition rates. INTRODUCTION Temperature extremes and water availability are considered to be the most important factors limiting production, activity of desert organisms and ecosystem processes in deserts (Noy-Meir, 1973, 1974; Whitford et al., 1981, Whitford et al., 1983). The frequency, amount and seasonal occurrence of precipitation are thought to affect productivity, litter decomposition and behavior of soil biota (Whitford et al., 1981). Noy-Meir (1973) proposed a pulse-reserve hypothesis for desert organisms in which rainfall sets off a of activity that is rapidly reduced, but some energy is stored reserved to await the next pulse. If desert organisms behave as predicted by the pulse reserve hypothesis, simulated rainfall events should trigger intense activity of various groups of soil organisms. Recent work indicates that moisture may not be as important as once thought as a regulator of the activity of soil biota. Whitford et al. (1982a) found no effect of rainfall on disappearance of leaf litter. They suggested that the desert soil decomposer community has evolved adaptations that allow those organisms to process surface litter independently of rainfall, and that soil temperature could be the most important parameter affecting the rate of litter removal. Hence, rates of decomposition in North American deserts are considerably greater than predicted based on the actual evapotranspiration and lignin content, which are good predictors of decomposition in more mesic environments (Whitford et al., 1983). Subterranean termites Gnathamitermes tubiformans are the most important processors of dead plant material and dung in the northern Chihuahuan desert (Johnson and Whitford, 1975; Whitford et al., 1982b). Termites are active aboveground during the rainy seasons, especially in the autumn, when they can be found in accumulations of litter or producing mud galleries on dead plant material (MacKay et al., 1985). Ettershank et al. (1980) reported that termites locate large food objects such as cow dung 'Send reprint requests to W. G. Whitford.

Some Biological and Chemical Changes in a North Queensland Soil Following Replacement of Rainforest with Araucaria cunninghamii (Coniferae: Araucariaceae)

(1) The soil nutrient levels, standing crop of litter and populations of soil and litter arthropods of a tropical Australian rainforest on the Atherton Tableland in north Queensland are compared with those of an adjacent 41-year-old hoop pine (Araucaria cunninghamdi D. Don) plantation. (2) Organic carbon levels in the rainforest soil were markedly higher than in the hoop-pine plantation as were the levels of nitrogen, acid-extractable phosphorus and exchangeable calcium, magnesium and potassium. (3) The standing crop of litter was markedly higher in the hoop-pine plantation than in the rainforest and showed strong seasonal variation related to the seasonality of litterfall and climatic events. Turnover rates (k) were lowest in the hoop-pine plantation. (4) Large litter arthropods were less abundant in the hoop-pine plantation while Acari and Collembola were more abundant in the rainforest soils. (5) It is suggested that the decline in organic matter and associated nutrients in the hoop-pine forest soil results from the loss of a large proportion of the plant nutrients from the ecosystem when the original rainforest was cleared. The subsequent establishment and growth of a hoop-pine plantation then lowered the existing soil nutrient supplies by transfer of nutrients into the vegetation.

The Effect of Foraging Army Ants on Leaf-Litter Arthropods

The effect of Eciton burchelli army ants (Hymenoptera: Formicidae) on leaf-litter arthropods was studied at Finca La Selva, Costa Rica. Analyses of leaf-litter samples indicated that both arthropod abundance and the number of taxa were reduced following the passage of foraging army ant swarms. Many of the arthropods in the path of an ant swarm escape; the escape tactics that we observed are presented. Full evaluation of the impact of army ant swarms on the arthropod community requires quantification of the rates of capture by both the army ants and the associated swarm-following birds, and of the rate of parasitization by flies that follow the ant swarms. ECITON BURCHELLI (FORMICIDAE: ECITONINAE) IS A COMMON, swarm-raiding army ant of the neotropical forests; its foraging swarms cover broad area and capture wide diversity of arthropods. Because colonies of E. burchelli have large daily intake of food, they presumably have substantial impact on litter arthropods in the areas in which they forage (Wilson 1971, Rettenmeyer et al. 1983). Their effectiveness in prey capture is not clear, however. In an early publication, Schneirla commented that they clear insect life rather completely from terrain over which they pass (1934, based partly on observations of Bates 1863 and Belt 1874). More recently, Schneirla (1949, 1971) and Rettenmeyer (1963) estimated that 30-50 percent of the litter arthropods escape E. burchelli swarms. In study of tropical leaf-litter arthropods, Williams (1941) analyzed the fauna from two plots the day after they were raided by army ants Labidus praedator and indicated that arthropod densities were reduced to a minimum. Franks (1982a, b; Franks & Bossert 1983; Franks & Fletcher 1983) has studied the effects of E. burchelli ants on leaf-litter communities in detail; his results will be referenced below when appropriate. In this study, we investigated the impact of foraging E. burchelli by measuring the densities of leaf-litter arthropods before and after the passage of army ant

Heavy metal content of forest litter arthropods as related to body-size and trophic level

Lead, zinc and cadmium concentrations were measured in thirteen species of small forest floor arthropods, inhabiting an area polluted by zinc factory emissions in the Netherlands. The species covered three orders of magnitude in body-sizes (3 μg to 6 mg), and a variety of feeding habits. Analysis of covariance was used to correct for weight effects on body burden. Metal analysis on an individual basis revealed large differences between species, even with similar feeding habits. The data are discussed in the light of two conflicting ecotoxicological theories which state that residues of chemicals either depend on body-size, or on the trophic level. The results show that, although body-size considerations may be relevant with respect to lead, both theories are inadequate with respect to zinc and cadmium. The concentrations of these metals seem to be connected to the physiological equipment of species, rather than to body-size or trophic level.

Litter Arthropod Populations in a Tropical Deciduous Forest: Relationships between Years and Arthropod Groups

Etude sur 40 mois de la variation des modalites de fluctuations des populations au cours des annees et des groupes d'arthropodes dans une foret tropicale humide de la Barro Colorado Island, Panama

Litter Moisture Content as a Determinant of Litter Arthropod Distribution and Abundance During the Dry Season on Barro Colorado Island, Panama

Animals generally are patchy in time and space. The causes of this pattern have been explored in only a few cases. We here present data on the relative amounts of migration and activity by litter arthropods during the dry season in artificially watered vs unmanipulated patches of litter on the forest floor of Barro Colorado Island, Panama. Watering significantly changed the physical environment of the litter. Litter moisture content increased by 37-70 percent (absolute increase 8-16%) and soil moisture content by 16-24 percent (absolute increase 4-8%). More and smaller arthropods were found in wetter patches. This effect was weak or variable in watered patches that had unmanipulated arthropod populations and strong in patches from which we had removed arthropods at the beginning of the experiment. Ant colonies were much more likely to migrate into wetter, empty areas, and more individuals were collected in these plots. Overall, more species of ants and more groups of arthropods were found in watered, empty plots. We thus demonstrate that at least part of the variance in plot-to-plot abundance of litter arthropods is related to litter moisture content. This may have strong effects on the community structure of litter arthropods. PATCHY SPECIES DISTRIBUTIONS are a common subject of biological investigations (review in Wiens 1976). Many species or groups are patchily distributed, often with no obvious biological explanation (Hairston and Byers 1954, Lloyd 1967). Litter and soil arthropods have been used as examples of this phenomenon (e.g., Macfadyen 1952, Lloyd 1963, Usher 1975). Soil or litter moisture content, insolation, or other abiotic factors frequently are suggested to be important in the formation of uneven distributions among sites (Usher 1970, 1975), but there have been only scattered experimental approaches to this question (Lloyd 1963, Gill 1969, Lussenhop 1976, Vandermeer et al. 1980, Whitford et al. 1981). We here present experimental data on arthropod abundance in leaf litter under a tropical semideciduous forest. Using 30 months of data, we previously suggested that the length of the rainy season and the distribution of rain showers in the dry season strongly affect litter arthropods (Levings and Windsor 1982). More litter arthropods were collected (1) when there was a short wet season with low late-wet-season rainfall and (2) when the dry season was punctuated with frequent, small rainshowers. Litter moisture content is more variable in the dry season than the wet season (Levings and Windsor 1982); wetter areas of litter are common on the forest floor during the dry season (pers. obs.). Small areas of moist litter may provide refuges from locally dry conditions for desiccation-intolerant species, permit continued reproduction or foraging activity, or be necessary for successful aesti-

Effect of Structure and Nutritional Quality of Litter on Abundances of Litter-dwelling Arthropods

Field manipulations of forest litter were conducted to measure effects of litter structure on abundances of forest floor arthropods in natural and artificial leaf litter. Artificial litter was made of nondecomposable vinyl. Both artificial and natural litter occurred in three structural treatments: flat, natural and complex. Using this design we could compare the interacting effects of litter as a trophic base and as a spatially heterogeneous environment on litter arthropods. In 1 of 4 months of the study, microAraneae were significantly (p< 0.05) more abundant in litter with complex structure: both natural and artificial. In contrast, Collembola and Acari abundances were unaffected by structural complexity of litter but were significantly (p<0.05) higher in natural leaves compared to artificial leaves. Abundances of dominant macroarthropod predators (Araneae) increased significantly (p<0.05) with increased litter structural heterogeneity in 1 of 4 study-months. Non-Araneae predators showed weak or no responses to litter complexity. Diplopods and isopods were more abundant in natural litter, while other nonpredatory macroarthropods were equally abundant in natural and artificial litter. INTRODUCTION Comparison of litter-dwelling arthropods from different forests shows arthropod abundance increased with increased litter depth and complexity (Lowrie, 1948; Luczak, 1963; Duffey, 1966; Berry, 1967; Huhta, 1971, 1976; Jocque, 1973; Uetz, 1975, 1976; McBrayer et al., 1971; Seastedt and Crossley, 1981; Bultman et al., 1982). Unfortunately, interpretation of these correlative studies is hampered because forests with structurally complex litter (composed of curly and twisted leaves rather than flat ones) tend also to have deep litter. [This correlation, however, does not always hold; litter of beech-maple forests is structurally simple (being primarily flat beech leaves) but often quite deep.] As a consequence of this general trend between litter depth and complexity, effects of these litter parameters on arthropod abundance were confounded. Further, effects of changes in litter depth on arthropod abundance may be caused by factors associated with litter depth, such as the habitat space or nutritional base available to arthropods. In sum, from previous work we cannot determine whether abundances of litter-dwelling arthropods are affected by the depth, structural complexity or nutritional quality of litter. To elucidate effects of litter complexity and nutritional quality on arthropod abundance, we conducted field experiments using natural and artificial leaves of varied structure and constant depth. Artificial, nonnutritive leaves provided a control for litter acting as a trophic base for the arthropod community; thus, influences of structure and nutritional content could be separated. We compared arthropod faunas inhabiting artificial leaves of varied structure (flat, natural and complex) to those of natural leaves of identical structural regimes.

Seasonal, Annual, and Among‐site Variation in the Ground Ant Community of a Deciduous Tropical Forest: Some Causes of Patchy Species Distributions

I examined patterns of species distributions in ground ants on Barro Colorado Island (BCI), Republic of Panama, using baited transect samples and Berlese extraction of litter arthropods. I sampled during wet and dry seasons in 1976 and 1977. All sites sampled were under closed—canopy rain forest at least 75 yr old. More species and more individuals were collected in wet than dry season using either method. Evenness of species abundance at baits also increased during the wet season. Ant activity was higher in 1977 than 1976 at all periods; this was correlated with increased rainfall during the dry season. Measures of species abundance and activity were positively correlated with protection from physical stresses. Over all seasons, fewer species and fewer individuals were collected at drier, sunnier sites. Patterns of seasonal and annual change were similar at bait transects and in Berlese samples. Species that were both active at baits and collected in Berlese samples varied in abundance the same way in both sampling methods. Several lines of evidence suggest that moisture availability is an important contributor to these patterns of among—site and among—season variation. First, ant activity, measured in several different ways, increased rapidly when moisture availability was increased, either through rainfall or through experimental watering during the dry season. Second, moisture availability may affect the distribution of suitable nest sites. This hypothesis was supported by differences in the number of colonies collected in Berlese samples from sites which differ in moisture availability. Third, the availability of food among sites may be correlated positively with soil moisture content, but there was not enough evidence to test this possibility. Fourth, there is some evidence that reduction of army ant raids in drier parts of the island during the dry season may concentrate the effects of these ant predators in moist, sheltered areas of BCI. Establishment and persistence of a given species in an area is a complex function of the availability of suitable food and nest sites and the strength of competitors and predators. Patchy species distributions were more the result of changes in the frequency of a species' occurrence among areas, than due to the existence of unique groups of species at separate sites, at least during the periods I sampled. Thus physical conditions were probably at least marginally acceptable to a large fraction of the fauna at all sites. However, differences in abundance and activity of ant species were correlated with changes in moisture availability. I have considered four hypotheses to account for these patterns, but they are by no means exhaustive. Moisture availability, acting through many intermediate steps, has major effects on the small—scale composition of ant faunas, even in a relatively sheltered environment like a tropical forest floor.

Distributions of Galapagos Ground Finches Along An Altitudinal Gradient: The Importance of Food Supply

I investigated the abundance, diet and food supply of ground finch species (Geospiza Gould) at different altitudes over a calendar year on Isla Pinta, Galapagos. The primary purpose of the study was to evaluate which of three alternative hypotheses best explains the present distributions of species along the vegetation gradient: habitat structure, food supply, or current interspecific competition. Isla Pinta was specifically chosen because Lack (1947) thought that on this island one species, G. difficilis, was competitively restricted to the highlands by the morphologically very similar species, G. fuliginosa. Four of the five species present were broadly distributed among habitats, and their altitudinal ranges overlapped considerably. The fifth, G. scandens, was rare and little was learned of its habit. G. difficilis ate mainly litter arthropods and gastropods, especially at high elevations. The remaining three species, G. fuliginosa, G. fortis, and G. magnirostris, were primarily granivorous, but each species consumed a different range of seed sizes. Diet overlap between species was highest when food production was high, and lowest when food was scarce. Seasonal declines in overlap seemed to be mainly due to finches' response to asynchronous food production and a gradual broadening of the available food spectrum. In the dry season the abundance and distribution of the four common species matched to varying degrees the abundance and distribution of the foods they consumed. Effects of current competition on these distributional patterns were not detected. Most Geospiza species did not seem to possess strict habitat requirements, and it is unlikely that variation in habitat structure greatly influenced distributions. One possible exception to this is G. difficilis, where litter supply may be important. Overall, the data suggest that while competition may be occurring between species, variation in food supply is currently a far more important determinant of distributions on Pinta.

The Effect of a Single Species of Avian Predator on the Arthropods of Aerial Leaf Litter

Recent studies have shown that insectivorous birds can have an effect on their arthropod prey populations. Holmes et al. (1979) found that enclosures in the understory of a temperate deciduous forest had a pronounced effect on Lepidoptera larvae. Solomon et al. (1976) showed that codling moth larvae had higher survivorship inside cages in an apple orchard in England. Dahlston and Copper (1979) found that birds reduced the population of overwintering tussock moth pupal egg masses, and Askenmo et al. (1977) reported the impact of birds on spider populations in a spruce forest. In all of these studies, many sympatric bird species may have been responsible for the observed increased mortality of arthropods. Here we report on an exclosure experiment conducted in moist tropical forest understory in Panama. The results indicate that predation by one species of insectivorous bird, Myrmotherula fulviventris (Checker-throated Antwren, Formicariidae), had a pronounced effect upon the arthropod prey populations in a single, easily sampled microhabitat. On our study area Myrmotherulafulviventris spends 98% of its foraging time searching aerial leaf litter for arthropods. Aerial leaf litter consists of dead leaves that fall from canopy trees and get caught in vegetation and vine tangles. As the leaves dry and curl they are colonized by many types of arthropods. These arthropods are abundant and many species appear to be unique to aerial leaf litter (J. A. Gradwohl, personal observation). While two or more species of aerial leaf litter foragers often occur in lowland Neotropical forests (Ridgely 1976, Munn and Terborgh 1979, Wiley 1980), on our study site there is only one, M. fulviventris. We have observed two species of antbird that usually forage by gleaning live foliage, checking dead leaves on our study site (Myrmotherula axillaris and Thamnophilus punctatus, Greenberg and Gradwohl 1980), but this behavior is very rare (<5% of total foraging repertoire). Myrmotherula fulviventris lives in pairs or small family groups on small (: 1.5-3 ha) territories which are co-defended with Microrhopias quixensis (Formicariidae). These areas are traversed several times daily, and areas of high use correspond with the presence of dense vine tangles (Gradwohl and Greenberg 1980). The density of aerial leaf litter is greater in vine tangles because tangles catch more falling leaves than vegetation in the open understory. In this study we exclosed vine tangles for 6 wk and found that aerial leaf litter arthropods were nearly twice as common inside the enclosures as outside. Because they experience heavy use by antwrens and contain high densities of dead leaves, we made vine tangles the focus of our exclosure experiment.

The Relation of Sodium and Water Balance to Survival in Sea Water of Estuarine and Freshwater Races of the Snakes Nerodia fasciata, N. sipedon and N. valida

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Feeding ecology of thirteen syntopic species of anurans in a seasonal tropical environment.

Thirteen species of anurans belonging to three families forage diurnally for arthropods in the leaf litter of the lowland rainforest at the Río Llullapichis in Amazonian Perú. This paper investigates the diets and patterns of coexistence in this group of ecologically similar species. All thirteen species use the forest floor habitat without apparent differentiation. Most species take prey in proportions significantly different from those occurring in the leaf litter and comprise two specialist guilds: dendrobatids and bufonids that eat hard-bodied, slow-moving arthropods such as ants and mites; and leptodactylids that eat soft-bodied, mobile arthropods, primarily orthopterans and large spiders. Dendrobates femoralis (Boulenger) is a generalist, taking prey in proportions not significantly different from those in the leaf litter. Within specialist guilds, body sizes of species vary and are correlated with the size of prey taken. Foraging behavior and predator defense also correlate with the type and sizes of prey taken. Ant specialists tend to be poisonous and active searchers, taking many small prey per day. Non-ant specialists are cryptic, sit-and-wait foragers that take few large prey per day. Similarity in diet within guilds tends tobe lowest in the dry season when food is less abundant, suggesting that food is in short supply in the dry season.

Seasonal variation in populations of panamanian litter frogs and their prey: A comparison of wetter and drier sites.

Various species of frogs and toads, belonging to the genera Bufo, Atelopus, Dendrobates, Colostethus, and Eleutherodactylus, occur in the leaf litter in rainforest in Panamá. This study compares the litter communities at two sites in Panamá: Pipeline Road, the drier site, and Carti Road, the wetter site. At both sites, frog abundance is greater in the dry season, when abundance of their prey, the litter arthropods, is greater. Species diversity does not change seasonally at either site; however, species diversity differs strikingly between sites, with Carti Road having the greater species diversity. Similarity in diet does not vary consistently with seasonal changes in food abundance at a single site or with differences in species diversity between sites. These results suggest that neither moisture nor food abundance alone influences the abundance or the diversity of litter frogs at these two sites in Panamá.