The Hemiptera (Insecta) communities of tropical rain forest in Sulawesi

The structure and composition of Hemiptera communities of tropical rain forest in Dumoga-Bone National Park, Sulawesi, Indonesia were investigated over a 1-year period. The aim was to investigate the extent to which insect samples, obtained using six different techniques, were representative of the whole community, and to explore temporal and spatial variation in Hemiptera community composition. Sampling techniques employed were Rothamsted light trapping, canopy fogging, malaise trapping at both ground and canopy level, flight interception trapping and yellow water pan trapping. Overlap between faunas collected using different techniques was surprisingly low emphasizing the limitations of using any single method to sample and thereby describe the Hemiptera community. Differences were observed at the species, family and suborder levels. Similarly, there were major differences in faunal composition between sites and diversity appeared to peak at elevations between 600–1000 m. Seasonal changes were also significant but generally lower than between methods or sites. Results are discussed in relation to factors such as food availability and host specialization and the efficacy of each sampling method is reviewed in relation to the biology of the different Hemiptera groups and the composition of the samples obtained.     

Cladocera in space and time: Analysis of lake sediments

Shells of Bosminidae and Chydoridae are quantitatively preserved in lake sediments. The chronological deposition of these remains provides the means for longterm observation of these Cladocera, both in terms of species and communities. Chydorid analysis, as based on subfossil assemblages, is an analysis of community and provides direct observation of community dynamics over extended periods of time. It has proved to be a valuable method to obtain information on the influence of environmental factors and time on community characteristics. Morphological variation inBosmina (Eubosmina) has been followed for some thousand years. This is of special interest for the evaluation of taxonomic rank (species, forms) if closely related taxa have co-existed. Bosmina successions, as well as shifts in the chydorid fauna, are related to environmental change. Thus, cladoceran analysis of lake sediments provides information on the developmental history of lakes and allows observation of the effects of longterm environmental changes, such as climatic changes and eutrophication.     

Benthic algal response to N and P enrichment along a pH gradient

Nutrient enrichment and its effect on benthic algal growth, community composition, and average cell size was assessed across two sites of differing pH within a single habitat. Nutrients were added using in situ substrata, which released either N, P, or no additional nutrients (controls) at each site for 21 days. Upon collection, chlorophyll and biovolume standing stocks of the attached algal microflora were measured. Chlorophyll concentration was different among all treatments, accumulating greatest on P, followed by N, and the least on C substrata (P < 0.001) and was highest at site-2 (P < 0.001), while total algal biovolume was highest on P compared to both N and C substrata (P < 0.05) and did not vary between sites. Increased growth on P substrata was due to the enhanced biovolume of filamentous green algae, although the affected taxa varied between sites. Biovolume to cell density ratios (as a measure of average cell size) were highest on P substrata over both N-enriched and control substrata (P < 0.05) and this pattern was similar between sites. Progression towards a community composed of larger cells following P enrichment observed along this pH gradient, seems to be related to the dominance of larger celled filamentous green algae. Thus, nutrients exhibited greater control on benthic algal growth than did changes in hydrogen ion concentration.Contribution number 581, Great Lakes Environmental Research LaboratoryContribution number 581, Great Lakes Environmental Research Laboratory     

Relative importance of temporal and spatial heterogeneity in the zooplankton community of an artificial reservoir

Zooplankton samples were collected monthly at three stations in Ogochi Reservoir during 1980, and the temporal and horizontal variations in the density of dominant taxa were evaluated by a standard 2-way ANOVA with random effects. The analysis revealed that horizontal is greater than temporal variation in the warm water season (> 18 °C), whereas temporal variation is greater in the cold water season (< 18 °C). Horizontal heterogeneity of the zooplankton community found in the warm water season seems to be associated with differences in site-specific conditions.     

Are galling insects better protected against parasitoids than exposed feeders?: a test using tenthredinid sawflies

ABSTRACT.

• 1 Data mostly from the published literature were used to assess the effect of galling on the number of parasitoid species per host species in the phylogeny of nematine sawflies from free external feeders (colonial and solitary) to leaf gallers and shoot gallers.
• 2 The strongest effects of galling were the total elimination of the species-rich cocoon-attacking guild of parasitoids, and eonymphal parasitoids, from the parasitoid community on shoot gallers, all of which are in the genus Euura.
• 3 All tachinid larval parasitoids were also eliminated by the galling habit.
• 4 The cumulative effects of these exclusions resulted in a decline in mean number of parasitoid species per host species from almost sixteen species on external colonial feeders to 4.0 species on shoot gallers.
• 5 General patterns in per cent parasitism by non-tachinid and tachinid larval parasitoids, eonymphal and cocoon parasitoids, on exposed feeders to shoot gallers, showed declines in non-tachinid attack and elimination of tachinid, eonymphal and cocoon parasitoids. But leaf gallers tended to be attacked more than exposed feeders by non-tachinid larval parasitoids.
• 6 The galling habit had a long-term impact by reducing the number of parasitoid species attacking nematine sawfly gallers and per cent mortality inflicted, so that natural enemies may have been important as a selective factor in the evolution of galling nematine sawflies.

     

Morphological dispersion of introduced Hawaiian finches: evidence for competition and a Narcissus effect

Summary Morphological analyses were conducted on finch species introduced to Oahu, Hawaii. As many as 25 species of finches representing four families (Emberizidae, Fringillidae, Ploecidae, Estrildidae) have been introduced to Oahu. Of these, 15 species currently have established wild populations. When compared with pools of 25 and 23 species introduced to Oahu, the 15 surviving species are morphologically overdispersed. This result is consistent with the hypothesis that competition has influenced the outcome of these introductions. We also tested the hypothesis that surviving introduced finches in one habitat (sugarcane fields) were morphologically overdispersed. When the seven surviving finch species found in sugarcane were compared with the pools of 25 and 23 species, they too were morphologically overdispersed. However, when the seven sugarcane species were compared with a species pool consisting of only the surviving 15 species found across Oahu, they were not morphologically overdispersed. This result suggests that morphological analyses of community structure based only on comparisons of assemblages of surviving species may be biased by a Narcissus effect.     

Buried seed population in the herbaceous lomas on Loma Ancon in the coastal desert of central Peru

Herbaceous lomas in the Peruvian coastal desert, of South America establish in spring, and its habitat is limited to the southern or southwestern slopes along the coast that are affected by thick fog. The time of appearance, the duration and the thickness of the fog vary greatly from year to year, so the lomas can grow only in habitats with enough water to, sustain seed germination and plant growth. This paper studies the species composition and density of the buried seed population, of the herbaceous lomas of Loma Ancon in order to clarify the mechanisms of the lomas' establishment. The mean number of species with viable seeds was about, 12 spp. m⁻² and that of dead seeds was about 22 spp. m⁻². The dominant species wereSolanum tuberiferum, S. pinnatifidum andNolana humifusa, both in viable and dead seeds. Viable seed density was about 5000–8000 seeds m⁻², which is comparable with the seed densities of other herbaceous communities. Dead seed density was about 15000–27000 seeds m⁻², or nearly three times the viable seed density, because the rate of decomposition was slow in the extremely dry conditions. The net increase of viable seeds by seed production was estimated at about 5000 seeds m⁻² in 1980, and the increase in the number of dead seeds was 2200 seeds m⁻².     

Fish size and habitat depth relationships in headwater streams

Summary Surveys of 262 pools in 3 small streams in eastern Tennessee demonstrated a strong positive relationship between pool depth and the size of the largest fish within a pool (P<0.001). Similarly, the largest colonizers of newly-created deep pools were larger than the colonizers of shallow pools. We explored the role of predation risk in contributing to the bigger fish — deeper habitat pattern, which has been noted by others, by conducting five manipulative field experiments in two streams. Three experiments used stoneroller minnows (Campostoma anomalum); one used creek chubs (Semotilus atromaculatus); and one used striped shiners (Notropis chrysocephalus). The stoneroller experiments showed that survival of fish approximately 100 mm in total length (TL) was much lower in shallow pools (10 cm deep) than in deep (40 cm maximum) pools (19% versus 80% survival over 12 d in one experiment) and added cover markedly increased stoneroller survival in shallow pools (from 49% to 96% in an 11-d experiment). The creek chub experiment showed that, as for stonerollers, pool depth markedly influenced survival: the chubs survived an average of 4.9 d in shallow pools and >10.8 d in deep pools. In the striped shiner experiment in shallow artificial streamside troughs, no individuals 75–100 mm TL survived as long as 13 d, where-as smaller (20–25 mm) fish had 100% survival over 13 d. The results of the experiments show that predation risk from wading/diving animals (e.g., herons and raccoons) is much higher for larger fishes in shallow water than for these fishes in deeper water or for smaller fish in shallow water. We discuss the role of predation risk from two sources (piscivorous fish, which are more effective in deeper habitats, and diving/wading predators, which are more effective in shallow habitats) in contributing to the bigger fish — deeper habitat pattern in streams.     

Observations on the relation between phytoplankton diversity and environmental factors in the Vaal River at Balkfontein,South Africa

The relationship between specific environmental factors as independent variables and temporal changes in phytoplankton community structure in the Vaal River (a turbid system) during 1984 was investigated by employing different diversity indices. Temporal changes in community structure reflected temporal changes in certain environmental factors. Phytoplankton diversity, measured with Shannon-Wie H' and Hurlbert PIE indices, was related firstly to discharge and discharge derived variables (such as SO₄, Si, N and P loading) and secondly to turbidity derived variables (such as euphotic zone depth). Discharge appears to be of prime importance in affecting diversity. Observations were made that shed new light on conditions contributing to the development of an August peak (dominated by Stephanodiscus hantzschii fo. tenuis and Micractinium pusillum) in phytoplankton concentration. Increased environmental stress may reduce the number of sensitive species, thus reducing interspecific competition between tolerant species which could then exploit the — for them — more favourable conditions resulting in an increase in their numbers to peak concentrations.