Effects of capacity on resource input and the aquatic metazoan community structure in phytotelmata

Aquatic metazoan communities in treeholes and bamboo stumps were studied on Tsushima Island, Japan, in March and June in relation to the habitat size and the resouce amount. The amount of leaf detritus increased with an increase in the capacity (volume) of the phytotelma. The input rate of leaves depended upon the opening area of the phytotelma. Twenty-one metazoan inhabitant taxa consisted of 17 dipteran saprophages, a helodid beetle larva, a nematoda, a naidid, and a predator,Toxorhynchites towadensis mosquito larva. Treeholes harbored 17 taxa and bamboo stumps 20; 16 taxa were common in both phytotelmata. The number of taxa and the biomass of metazoa per phytotelma was positively correlated with the capacity. The densities of dominant saprophages such as helodid, chironomid, andCulicoides larvae were positively correlated with the capacity of phytotelmata, and the variation in their abundance contributed much to the variation in the species composition in individual phytotelmata. With an increase in capacity, treeholes harbored more helodids andCulicoides, whereas bamboo stumps harbored more chironomids andDasyhelea. Thus, the amount of resource, species richness and biomass per phytotelma largely depended upon the capacity, and the difference in community structure between treeholes and bamboo stumps was attributable to the differential colonization patterns of different taxa.     

Searching clusters of community composition along multiple spatial scales: a case study on aquatic invertebrate communities in bamboo stumps in West Timor

We examined spatial heterogeneity at multiple scales in composition of the aquatic invertebrate communities in bamboo stumps in a mountainous area of West Timor. We partitioned the study area (ca. 15,000 m²) at five levels of patchiness: two sites, four sub-sites, eight super-clumps, 14 clumps, and 84 stumps. Similarity of community composition between stumps varied more than expected from independent occurrence of each taxon in comparisons within any levels of patches. Negative association was frequently detected among taxa. These results indicate heterogeneity in community composition at a stump level. At higher levels, similarity among stumps within each site was greater than expected from null models which assumed no spatial heterogeneity, and similarities among super-clumps, sub-sites and between sites in a whole area were lower than expected from the null models. The observed patterns in similarities among subsets of the community and distribution of each taxon were mostly consistent with the models which assumed site-level heterogeneity. Therefore, we conclude that the community in this area was spatially heterogeneous at stump and site levels. The relationship between mean intra- and inter-specific crowding suggested that the site level habitat heterogeneity might reduce the chance of encounters between two predators, the larvae of the Toxorhynchites mosquito and the Brachyceran fly.     

Microhabitat size distribution affects local difference in community structure: Metazoan communities in treeholes

I studied the effect of treehole (microhabitat) size distribution in local habitats on geographic difference in aquatic metazoan community structure by comparing differences between two sites on Iriomote Island, and between Iriomote Island (subtropical) and Tsushima Island (temperate), in southwestern Japan. In treeholes at each local site, the amount of litter, the species richness and total biomass of metazoa were positively correlated with treehole capacity. Between the two sites on Iriomote Island (Shirahama and Komi), the amount of litter, biomass and species number per treehole was greater at Komi where the mean and variance of treehole size were greater, while the dependencies of these parameters on treehole capacity were common to both sites. Total species number was larger at Komi (2 predators and 20 saprophages) than at Shirahama (1 predator and 19 saprophages). Most of the dominant taxa colonized larger treeholes with higher probabilities, although one taxa showed the opposite trend. Treeholes on Tsushima were smaller than those on Iriomote. The metazoan fauna in treeholes consisted of 15 saprophages on Tsushima, being less richer than that on Iriomote Island which had 2 predators and 21 saprophages. However, the dependencies of litter amount and biomass on treehole capacity did not differ significantly between the islands, although treeholes on Iriomote harbored a greater number of species per treehole than those on Tsushima. This study indicated that there are general correlates between community structure within individual treeholes (infracommunity structure) and treehole capacity (microhabitat size). Therefore, microhabitat-size distribution is potentially a significant constraint of local community structure, and its variation may contribute to the variation in local and regional species richness.     

Habitat stability and the larval mosquito community in treeholes and other containers on a temperate Island

The temporal fluctuation of water levels and the presence of mosquito larvae were investigated for four types of small container habitats (treeholes, bamboo stumps, cemetery stone vases, and cemetery stone vessels) on Kabeshima Island in Kyushu, southwestern Japan. The probability that containers held water was positively correlated with the quantity of the preceding rainfall and with the depth and volume of the containers. It was estimated that dehydration occurred more regularly in autumn and winter than in summer. The probability that mosquito larvae were present in each type of container was positively correlated with habitat stability in terms of the probability of the existence of standing water and the coefficient of variation of the water level. Twelve species of mosquito larvae, including two rare predators, were found. Species composition differed between the different types of container. Although 4 to 10 species used each type of container, the median number of species per container was two for treeholes and bamboo stumps, and one for the others. The dominant species wasTripteroides bambusa in treeholes and bamboo stumps,Aedes albopictus in stone vases, andA. japonicus in stone vessels. The larval mosquito community, which lacked major predators, possessed the following features that may facilitate the coexistence of many species: (1) niche segregation amongst species in terms of their selection of container types; (2) an aggregated distribution of the individual species among containers of the same type; (3) high intraspecific mean crowding (and hence probably intense intraspecific competition) in the dominant species in each type of container; (4) independent species associations within the same type of container; and (5) low interspecific mean crowding (and hence probablynot intense interspecific competition) between species in the same type of container.     

Attracted to the enemy: Aedes aegypti prefers oviposition sites with predator-killed conspecifics

Oviposition habitat choices of species with aquatic larvae are expected to be influenced by both offspring risk of mortality due to predation, and offspring growth potential. Aquatic predators may indirectly influence growth potential for prey by reducing prey density and, for filter-feeding prey, by increasing bacterial food for prey via added organic matter (feces, partially eaten victims), creating the potential for interactive effects on oviposition choices. We tested the hypothesis that the mosquito Aedes aegypti preferentially oviposits in habitats with predatory Toxorhynchites larvae because of indirect effects of predation on chemical cues indicating bacterial abundance. We predicted that A. aegypti would avoid oviposition in sites with Toxorhynchites, but prefer to oviposit where bacterial food for larvae is abundant, and that predation by Toxorhynchites would increase bacterial abundances. Gravid A. aegypti were offered paired oviposition sites representing choices among: predator presence; the act of predation; conspecific density; dead conspecific larvae; and bacterial activity. A. aegypti preferentially oviposited in sites with Toxorhynchites theobaldi predation, and with killed conspecific larvae, but failed to detect preferences for other treatments. The antibiotic tetracycline eliminated the strongest oviposition preference. Both predation by Toxorhynchites and killed larvae increased bacterial abundances, suggesting that oviposition attraction is cued by bacteria. Our results show the potential for indirect effects, like trophic cascades, to influence oviposition choices and community composition in aquatic systems. Our results suggest that predators like Toxorhynchites may be doubly beneficial as biocontrol agents because of the attraction of ovipositing mosquitoes to bacterial by-products of Toxorhynchites feeding.     

Testing the nest-homing abilities of a phytotelm-breeding frog, Chirixalus eiffingeri (Rhacophoridae)

We conducted a manipulative experiment to assess the homing of female Chirixalus eiffingeri to the nest. There were three experimental treatments and a control. For the control treatment, bamboo stumps were cut off at the base and reattached. In the first experimental treatment, when stumps were displaced 1 m, the proportion of stumps attended by females and the growth of tadpoles did not differ from the results of the control treatment, suggesting the 1-m stump displacement did not affect the nest homing of female frogs. In the second experimental treatment, when a bamboo stump was displaced 1 m and a new bamboo stump with tadpoles was put in its place, some females fed tadpoles in the displaced stump (3/12), but some fed tadpoles in the stump (3/12) at the original site. This finding suggests that the addition of a new stump confused the female frogs spatially, which resulted in females feeding the tadpoles in either stump. In the third experimental treatment, when a bamboo stump was displaced 1 m and a new stump without tadpoles was added at the original site, some female frogs fed tadpoles in the displaced stump (5/12) but some laid trophic eggs in the stump (4/12) at the original site, also indicating the female frogs were confused spatially. The overall results support the hypothesis that females rely on the spatial distribution of a nest stump, relative to other bamboo stumps, for nest homing to feed their offspring, and that stump location is an important cue to the nest homing of females.     

Association of immature mosquitoes and predatory insects in urban rain pools

Distribution among pools of six mosquito species and 23 predatory insect taxa were studied in temporary rain pools during the summer and fall season in Buenos Aires city. Both mosquito immatures and predators were disproportionally more abundant in pools with high flooded surface, depth, and duration. Mosquito immatures differed in their habitat use with respect to predators. Among mosquitoes, Ochlerotatus albifasciatus showed a different pattern when compared to the remaining culicids. More culicid and predatory insect taxa colonized the pools in those flooding events of longer duration. Ochlerotatus albifasciatus was the only mosquito species recorded during short duration events and the first one in colonizing the pools in long duration events. This species shared the pools mainly with early arriving adult predators. Three Culex species were recorded later and showed higher coexistence with most of the predatory taxa, mainly immatures of the genera Tropisternus, Rhantus, Liodessus, and Belostoma. A high heterogeneity between pools and seasons was observed. Multiple regression analyses showed a negative relationship of per capita change of Culex species with large-sized predators only in those cases where predators were collected in high abundances during the summer. No negative relationship of predators was detected in relation to per capita change and abundance of Ochlerotatus albifasciatus. Differences in duration of about two to three weeks seemed to significantly affect the abundance of both culicid and predatory taxa, suggesting that the urban pools analyzed in this study are on the extreme of suitable conditions for these aquatic insects.     

Predatory fish loss affects the structure and functioning of a model marine food web

The rate of species loss is increasing on a global scale and predators are most at risk from human-induced extinction. The effects of losing predators are difficult to predict, even with experimental single species removals, because different combinations of species interact in unpredictable ways. We tested the effects of the loss of groups of common predators on herbivore and algal assemblages in a model benthic marine system. The predator groups were fish, shrimp and crabs. Each group was represented by at least two characteristic species based on data collected at local field sites. We examined the effects of the loss of predators while controlling for the loss of predator biomass. The identity, not the number of predator groups, affected herbivore abundance and assemblage structure. Removing fish led to a large increase in the abundance of dominant herbivores, such as Ampithoids and Caprellids. Predator identity also affected algal assemblage structure. It did not, however, affect total algal mass. Removing fish led to an increase in the final biomass of the least common taxa (red algae) and reduced the mass of the dominant taxa (brown algae). This compensatory shift in the algal assemblage appeared to facilitate the maintenance of a constant total algal biomass. In the absence of fish, shrimp at higher than ambient densities had a similar effect on herbivore abundance, showing that other groups could partially compensate for the loss of dominant predators. Crabs had no effect on herbivore or algal populations, possibly because they were not at carrying capacity in our experimental system. These findings show that contrary to the assumptions of many food web models, predators cannot be classified into a single functional group and their role in food webs depends on their identity and density in 'real' systems and carrying capacities.     

Pigeons as seed predators and dispersers of figs in a Malaysian lowland forest

Seven pigeon species fed on figs from at least 22 Ficus taxa at a lowland forest site in Peninsular Malaysia. Forest pigeons of the genus Treron are fig-eating specialists. Although these are important fig-seed predators, at least some of the population, and pigeons from other genera, potentially disperse Ficus seeds to distant sites.     

Local and Regional-Scale Food Web Structure in Nepenthes alata Pitchers1

Tropical Nepenthes pitcher plants provide small, isolated aquatic habitats. We examined inter-pitcher variation in the community structure of the inhabitants of Nepenthes alata Blanco in West Sumatra, focusing on the conditions of the pitchers, bacterial density in the pitcher fluid, density and biomass of metazoan inhabitants, and the frequencies of interspecific encounters. Older pitchers contained more insect carcasses. The bacterial density increased with the age of the pitchers, but decreased in withered pitchers that contained finely decomposed detritus. In live pitchers, the bacterial density, the density, mass and species richness of metazoa, and the number of trophic levels per pitcher were positively correlated with detrital mass, which was correlated with volume of pitcher fluid. The metazoan fauna from N. alata consisted of 4 predators and 12 saprophages, among the richest known for Nepenthes species. However, each individual pitcher harbored a limited numbers of species, owing to (1) the low incidence of many species, and (2) the aggregated distribution and different temporal colonization pattern of major species. Six dipteran taxa (one predator and five saprophages) accounted for the bulk of metazoan inhabitant biomass. Of 48 combinations of predator-prey encountered, only four occurred frequently (in > 30% of pitchers), which included two predators and three saprophages. Thus, individual pitchers harbored relatively simple communities despite the regional species richness, and only limited kinds of predator-prey encounters seemed to occur frequently in the regional food web. The local-scale properties of the subdivided communities presented here provide the basic information for understanding the maintenance of regional species richness and food web complexity.     

Analysis of population dynamics of diamondback moth, (Plutella xylostella (Lepidoptera: Plutellidae)) at two sites in central Ethiopia, with particular reference to parasitism

Change in diamondback moth (DBM) (Plutella xylostella L.) numbers and level of parasitism on head cabbage (Brassica oleracea var. capitata) was monitored for two seasons in two different agroecological zones representing the highland and lowland brassica-producing areas of central Ethiopia in 2001 and 2002. Two to three generations in the highland site and three to five generations in the lowland site per cabbage growing season were observed. Three parasitoids were recorded at both locations. These were Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae), Diadegma sp. (Hymenoptera: Ichneumonidae), and Apanteles sp. (Hymenoptera: Braconidae). Diadegma sp. was the dominant parasitoid at the highland site and O. sokolowskii was dominant at the lowland site. Rainfall and maximum temperature significantly influenced DBM numbers and parasitoid activity at the highland experimental site.     

Biomass distribution of different-aged needles in young and old Pinus cembra trees at highland and lowland sites

Conifer needles of different ages perform differently in ecophysiology. However, no study has investigated the biomass distribution of different-aged needles in a tree crown or/and a stand canopy. We carried out a study on young (∼50 years old) and old (∼200 years) Pinus cembra L. trees at highland (2100–2300 m a.s.l.) and lowland (570 m) sites in Switzerland. We found that both the young and the old trees living in the highlands had more needle biomass per tree than the same-aged trees of the same species living in the lowlands. This is mainly due to the greater longevity of needles in highland trees. It reflects the strategic responses of trees to low resource availability or high abiotic stress level. Having older needles increases the time that nutrients are resident in trees in less favorable environments, and compensates for shorter growing period in cold temperatures.     

Comparative study of the breeding success of Whooper Swans Cygnus cygnus nesting in upland and lowland regions of Iceland

The study assessed the reproductive success at different stages of the breeding season of Whooper Swans Cygnus cygnus from two geographically distinct areas of Iceland, one an upland and the other a lowland region. Censuses made at both sites indicated that the majority of the birds did not attempt to breed and that annual recruitment came from 30 to 40% of the population. Individual females tended to lay more eggs in the lowlands, with a mean clutch-size of 4.7 eggs, compared with 3.8 eggs per clutch in the highlands. A mean brood-size of 3.1 cygnets was obtained at both the highland and the lowland sites in August but the highland cygnets were significantly smaller and lighter. The difference in cygnet size could be attributable to one or a combination of factors including age differences and habitat variables. Lowland adults were significantly heavier than those from the highlands, which reinforced the view that habitat quality was superior at the lowland site. There was no difference in the feather length recorded for adult swans moulting in the two study areas, indicating that the moult occurred concurrently in the highlands and lowlands. The number of cygnets lost per brood between ringing and resighting in the wintering range was significantly higher for the highland swans, although the number of highland families relocated was small. The results indicate that birds from different breeding areas may contribute disproportionately to the percentage of juveniles reared annually in the population.     

Predation pressure shapes brain anatomy in the wild

There is remarkable diversity in brain anatomy among vertebrates and evidence is accumulating that predatory interactions are crucially important for this diversity. To test this hypothesis, we collected female guppies (Poecilia reticulata) from 16 wild populations and related their brain anatomy to several aspects of predation pressure in this ecosystem, such as the biomass of the four major predators of guppies (one prawn and three fish species), and predator diversity (number of predatory fish species in each site). We found that populations from localities with higher prawn biomass had relatively larger telencephalon size as well as larger brains. Optic tectum size was positively associated with one of the fish predator’s biomass and with overall predator diversity. However, both olfactory bulb and hypothalamus size were negatively associated with the biomass of another of the fish predators. Hence, while fish predator occurrence is associated with variation in brain anatomy, prawn occurrence is associated with variation in brain size. Our results suggest that cognitive challenges posed by local differences in predator communities may lead to changes in prey brain anatomy in the wild.     

The Lethal Fungus Batrachochytrium dendrobatidis Is Present in Lowland Tropical Forests of Far Eastern Panamá

The fungal disease chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd), is one of the main causes of amphibian population declines and extinctions all over the world. In the Neotropics, this fungal disease has caused catastrophic declines in the highlands as it has spread throughout Central America down to Panamá. In this study, we determined the prevalence and intensity of Bd infection in three species of frogs in one highland and four lowland tropical forests, including two lowland regions in eastern Panamá in which the pathogen had not been detected previously. Bd was present in all the sites sampled with a prevalence ranging from 15–34%, similar to other Neotropical lowland sites. The intensity of Bd infection on individual frogs was low, ranging from average values of 0.11–24 zoospore equivalents per site. Our work indicates that Bd is present in anuran communities in lowland Panamá, including the Darién province, and that the intensity of the infection may vary among species from different habitats and with different life histories. The population-level consequences of Bd infection in amphibian communities from the lowlands remain to be determined. Detailed studies of amphibian species from the lowlands will be essential to determine the reason why these species are persisting despite the presence of the pathogen.     

Scorpion diversity in two different habitats in the Arid Chaco,Argentina

Scorpions are one of the most important taxa of predators in terms of density, biomass, and diversity in various areas of the world. In this study, we compared population- and community-level data between a mature and a secondary forest in the Chancaní Reserve (Córdoba, Argentina). Scorpions were collected using pitfall traps (54 nights per site), and their nocturnal activity was observed by means of UV light (26 nights per site) over 7 months. Seven species of scorpions (1964 individuals) were observed in the study area (Bothriuridae and Buthidae). Brachistosternus ferrugineus composed >74 % of all individuals and was numerically dominant in most months. It was the most common species sampled with UV light method in all months (85.73 % in mature and 81.80 % in secondary forest). Timogenes elegans was the most common species sampled with the pitfall traps method in secondary forest (48.58 %). General sex ratio (males:females) for B. ferrugineus was 1:1.24 and for T. elegans was 1:0.53. The Shannon index was not significantly different between sites. Species richness was similar, and the Jaccard index was Cs = 0.86, indicating that both sites share 86 % of the species. Tityus confluens was the only species not shared between sites. Our results indicate that species composition in regenerating forest resembles that of primary forest after c. 15 years, but the relative abundances of these species differ.     

Small stonefly predators affect microbenthic and meiobenthic communities in stream leaf packs

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Genetic analysis of adaptation differences between highland and lowland tropical maize using molecular markers

Molecular-marker loci were used to investigate the adaptation differences between highland and lowland tropical maize. An F₂ population from the cross of two inbred lines independently derived from highland and lowland maize germplasm was developed, and extracted F_3:4 lines were phenotype in replicated field trials at four thermally diverse tropical testing sites, ranging from lowland to extreme highland (mean growing season temperature range 13.2–24.6°C). Traits closely related with adaptation, such as biomass and grain yield, yield components, days from sowing to male and female flowering, total leaf number, plant height and number of primary tassel branches (TBN), were analyzed. A large line × environment interaction was observed for most traits. The genetic basis of this interaction was reflected by significant, but systematic, changes from lowland to highland sites in the correlation between the trait value and genomic composition (designated by the proportion of marker alleles with the same origin). Joint analysis of quantitative trait loci (QTLs) over sites detected 5–8 QTLs for each trait (except disease scores, with data only from one site). With the exception of one QTL for TBN, none of these accounted for more than 15% of the total phenotypic variation. In total, detected QTLs accounted for 24–61% of the variation at each site on average. For yield, yield components and disease scores, alleles generally favored the site of origin. Highland-derived alleles had little effect at lowland sites, while lowland-derived alleles showed relatively broader adaptation. Gradual changes in the estimated QTL effects with increasing mean site temperature were observed, and paralleled the observed patterns of adaptation in highland and lowland germplasm. Several clusters of QTLs for different traits reflected the relative importance in the adaptation differences between the two germplasm types, and pleiotropy is suggested as the main cause for the clustering. Breeding for broad thermal adaptation should be possible by pooling genes showing adaptation to specific thermal regimes, though perhaps at the expense of reduced progress for adaptation to a specific site. Molecular marker-assisted selection would be an ideal tool for this task, since it could greatly reduce the linkage drag caused by the unintentional transfer of undesirable traits. Received: 10 October 1998 / Accepted: 9 April 1999     

Distributions of larval mosquitoes among bamboo-stump pools which vary in persistence and resource input

We studied the seasonal occurrence and the distribution patterns of larval mosquitoes in a bamboo grove in northern Kyushu, Japan. The number of pools was large from June to August and was small in winter. Deep stumps and semi-closed-type stumps held water more persistently than shallow and open-type stumps, respectively. Open-type stumps trapped more leaves than semi-closed-type stumps and the number of leaves trapped in the open-type stump was positively correlated with the area of the pool. The incidences ofTripteroides bambusa andAedes albopictus were low early in their breeding season and gradually increased thereafter. In August, the density ofT. bambusa larvae per pool was higher in the old (>2 months) pools than in the new pools and was positively correlated with the depth of the stumps. In contrast, the density ofA. albopictus did not differ significantly between the new-and old pools and was not significantly correlated with the depth of the stump. The density ofA. albopictus was positively correlated with the number of leaves that had been trapped in the stump, whereas the density ofT. bambusa was not. In addition to the seasonal fluctuation in habitat-patch availability, the variations in habitat persistence and resource input among bamboo stumps may facilitate the coexistence of the two mosquitoes that were differentially limited by these factors.     

Biomass Harvest from Natural Willow Rings around Prairie Wetlands

The study followed the harvest of natural willow from three wetlands using a prototype modified agricultural round baler nicknamed a Bio-Baler. The study reports fuel characteristics and combustion testing of biomass harvested from natural willow rings. Composition of native willow species in the harvested willow rings was determined. We specifically measured regrowth of the biomass and number of regenerated stems per stump 1 year after harvest to determine how different willow species responded to mechanical biomass cutting with the Bio-Baler. The results of combustion testing for the natural willow were essentially similar to those with “conventional” wood chips or planted willows. The ash content was approximately 1.65%, slightly lower than for planted willow plantations. The calorific value of the natural willow was 19.6 MJ kg^?1 (dry basis) similar to what is expected for wood and planted willow. Four Salix species (Salix bebbiana Sarg., Salix petiolaris Sm., Salix eriocephala Michx., and Salix discolor Muhl) were identified in the willow rings. Stem biomass increased for all species except S. bebbiana after willow was harvested with the Bio-Baler. Overall, willow regeneration was not affected by mechanical harvesting compared to hand cutting. Regenerated stem density was 93 stems per square meter for mechanically harvested stumps compared to 105 stems per square meter for hand-pruned stumps. Based on the results, biomass harvested from natural willow rings has acceptable fuel characteristics when compared to purpose-grown willows and mechanical harvest with a Bio-Baler does not have a negative effect on willow regeneration.