Leaf Litter Arthropods Research Articles

Response of soil and leaf litter microarthropods to forest application of diflubenzuron

The objective of this study was to assess the effects of forest application of diflubenzuron (Dimilin®), a gypsy moth suppressant, on nontarget invertebrates in litter and soil on the forest floor. Four experimental watersheds (two treatment and two reference) in the Fernow Experimental Forest, West Virginia, were sampled for two years before and one year after application of diflubenzuron (70 g ha−1, AI). Soil and leaf litter arthropods were monitored before and after application using soil cores and litter bag colonization samplers. Frequency analysis, BACIP, and ANOVA were used to analyse the data for diflubenzuron treatment effects. During the 36 month study, soil core samples were dominated by mites (49%) and springtails (28%). A total of 19 taxonomic groups were suitable for statistical analysis. We detected no significant treatment effects based on total organism counts or counts by trophic categories (p < 0.05). There were no significant treatment effects for populations of major taxonomic groups, except for Araneae (spiders). Analysis of leaf litter bags also showed no significant differences in total numbers of invertebrates or in trophic categories between treated and reference watersheds during the 12 month post-treatment study. Density of one species of springtail (Sminthurus purpurescens) and springtails as a group were significantly lower in treated watersheds. High variation was associated with both soil core and leaf bag samples; because of this variation, a significance level of 0.05 should be considered very conservative. Long-term trends in soil biota were evident, demonstrating the need for well-established pre-treatment baseline data for pesticide impacts on soil organisms

Dietary source for skin alkaloids of poison frogs (Dendrobatidae)?

A wide range of alkaloids, many of which are unknown elsewhere in nature, occur in skin of frogs. Major classes of such alkaloids in dendrobatid frogs are the batrachotoxins, pumiliotoxins, histrionicotoxins, gephyrotoxins, and decahydroquinolines. Such alkaloids are absent in skin of frogs (Dendrobates auratus) raised in Panama on wingless fruit flies in indoor terraria. Raised on leaf-litter arthropods that were collected in a mainland site, such terraria-raised frogs contain tricyclic alkaloids including the beetle alkaloid precoccinelline, 1,4-disubstituted quinolizidines, pyrrolizidine oximes, the millipede alkaloid nitropolyzonamine, a decahydroquinoline, a gephyrotoxin, and histrionicotoxins. The profiles of these alkaloids in the captive-raised frogs are closer to the mainland population ofDendrobates auratus at the leaf-litter site than to the parent population ofDendrobates auratus from a nearby island site. Extracts of a seven-month sampling of leaf-litter insects contained precoccinelline, pyrrolizidine oxime236 (major), and nitropolyzonamine (238). The results indicate a dietary origin for at least some "dendrobatid alkaloids," in particular the pyrrolizidine oximes, the tricyclic coccinellines, and perhaps the histrionicotoxins and gephyrotoxins.

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.

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

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.

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.