An altitudinal comparison of caterpillar (Lepidoptera) assemblages on Ficus trees in Papua New Guinea

Aim This analysis of caterpillar (Lepidoptera) beta‐diversity between tropical lowlands and highlands attempts to separate the effects of between‐site (1) turnover of herbivore species on particular host plants, (2) changes in host use by herbivores, and (3) turnover of plant species on changes in herbivore assemblages. Location Two rain forest areas 130 km and 1700 altitudinal metres apart were studied in Papua New Guinea: one in the lowlands (100 m a.s.l.) on the northern coast of the island and one in the central New Guinean cordillera at 1800 m a.s.l. Methods The analysis is based on caterpillar feeding records obtained by quantitative sampling and rearing of caterpillars from four Ficus species studied in the mountains and 21 Ficus species and 62 plant species from other genera and families studied in the lowlands, including three Ficus species studied in both areas. Results Only 17% of species feeding on Ficus in the highlands also occurred in the lowlands. These species represented 1–46% of individuals in caterpillar assemblages on particular Ficus hosts. Widespread species included both Ficus specialists and generalists feeding on numerous plant families. Some of the Ficus specialists changed their preferred host species with altitude. High species turnover was not explained by changes in the species composition of host plants with altitude as lowland and montane assemblages feeding on the same Ficus species showed high turnover. Despite the rarity of widespread caterpillars, the lowland and montane Ficus assemblages were remarkably similar in their dominance structure, species richness, host specificity, generic composition and familial composition. Main conclusions Ficus‐feeding Lepidoptera assemblages between tropical lowlands and highlands are characterized by substantial species turnover not explained by altitudinal changes in the composition of the vegetation. Further, species‐rich plant genera can support caterpillar assemblages with relatively low beta‐diversity compared with species‐poor genera as caterpillars can switch their host preferences from one congeneric host species to another along an altitudinal gradient. Closely related plant species can thus represent a broad, continuously distributed resource along such gradients.     

Community structure of arboreal caterpillars within and among four tree species of the eastern deciduous forest

Abstract.  1. A seasonally replicated experimental design was used to address the question of how differences within and among host tree species affect arboreal caterpillar communities.
2. Seasonal variation influenced caterpillar community composition most significantly, and the similarity among caterpillar assemblages did not necessarily follow the pattern of phylogenetic relatedness among host trees.
3. Species richness and abundance of caterpillars were higher on oaks and maples than on American beech. Diversity partitioning models revealed that β diversity was only occasionally greater or less than expected by chance alone.
4. When β diversity was significant, values tended to be greater than expected by chance among replicate trees within each species and lower than expected by chance among the four tree species.
5. Differences among trees appeared important for determining patterns of species presence/absence for rare species and influencing patterns of species dominance within caterpillar assemblages. Differences among tree species had a significant effect on overall lepidopteran community composition and mean species diversity (i.e. α diversity).
6. Because β diversity of caterpillars among host trees was lower than expected by chance, host specificity within the Lepidoptera may be less prevalent than thought previously.     

Predictably simple: assemblages of caterpillars (Lepidoptera) feeding on rainforest trees in Papua New Guinea

Predictability in the composition of tropical assemblages of insect herbivores was studied using a sample of 35,952 caterpillars (Lepidoptera) from 534 species, feeding on 69 woody species from 45 genera and 23 families in a lowland rainforest in Papua New Guinea. Caterpillar assemblages were strongly dominated by a single species (median 48% of individuals and 49% of biomass). They were spatially and temporally constant (median normalized expected species shared (NESS) similarity between assemblages from the same host was greater than or equal to 0.85 for three sites 8-17 km apart as well as for three four-month periods of the year). Further, the median presence of species was 11 months per year. Assemblages on hosts from different families and genera were virtually disjunct (NESS similarity less than 0.05) as the caterpillars were mostly specialized to a single plant family (77% of species) and, within families, to a single genus (66% of species), while capable of feeding on multiple congeneric hosts (89% of species). The dominance of caterpillar assemblages by a small number of specialized species, which also exhibited low spatial and temporal variability, permitted robust and reliable estimates of assemblage composition and between-assemblage similarity from small samples, typically less than 300 individuals per host plant. By contrast, even considerably larger samples were insufficient for estimates of species richness. A sample of 300 individuals was typically obtained from 1,050 m(2) of foliage sampled during 596 tree inspections (i.e. a particular tree sampled at a particular time) in the course of 19 sampling days (median values from 69 assemblages). These results demonstrate that, contrary to some previous suggestions, insect herbivore assemblages in tropical rainforests have a predictable structure and, as such, are amenable to study.     

Plant phylogeny drives arboreal caterpillar assemblages across the Holarctic

1. Assemblages of insect herbivores are structured by plant traits such as nutrient content, secondary metabolites, physical traits, and phenology. Many of these traits are phylogenetically conserved, implying a decrease in trait similarity with increasing phylogenetic distance of the host plant taxa. Thus, a metric of phylogenetic distances and relationships can be considered a proxy for phylogenetically conserved plant traits and used to predict variation in herbivorous insect assemblages among co‐occurring plant species.
2. Using a Holarctic dataset of exposed‐feeding and shelter‐building caterpillars, we aimed at showing how phylogenetic relationships among host plants explain compositional changes and characteristics of herbivore assemblages.
3. Our plant–caterpillar network data derived from plot‐based samplings at three different continents included >28,000 individual caterpillar–plant interactions. We tested whether increasing phylogenetic distance of the host plants leads to a decrease in caterpillar assemblage overlap. We further investigated to what degree phylogenetic isolation of a host tree species within the local community explains abundance, density, richness, and mean specialization of its associated caterpillar assemblage.
4. The overlap of caterpillar assemblages decreased with increasing phylogenetic distance among the host tree species. Phylogenetic isolation of a host plant within the local plant community was correlated with lower richness and mean specialization of the associated caterpillar assemblages. Phylogenetic isolation had no effect on caterpillar abundance or density. The effects of plant phylogeny were consistent across exposed‐feeding and shelter‐building caterpillars.
5. Our study reveals that distance metrics obtained from host plant phylogeny are useful predictors to explain compositional turnover among hosts and host‐specific variations in richness and mean specialization of associated insect herbivore assemblages in temperate broadleaf forests. As phylogenetic information of plant communities is becoming increasingly available, further large‐scale studies are needed to investigate to what degree plant phylogeny structures herbivore assemblages in other biomes and ecosystems.

     

An alien in an archipelago: Spathodea campanulata and the geographic variability of its moth (Lepidoptera) communities in the New Guinea and Bismarck Islands

Aim This analysis of moth (Lepidoptera) communities colonizing an alien tree invading secondary rain forest vegetation in Melanesia examines the predictability of insect herbivorous communities across distances of tens to thousands of km and the effect of dispersal barriers on community composition in the tropics. Location Six secondary rain forest sites were studied within four equidistant yet distinct geographic areas of the New Guinea mainland and the Bismarck Archipelago, including two watershed areas (Madang and Sepik) on mainland New Guinea and the adjacent large island of New Britain and small island of Unea. Methods The analysis is based on feeding records obtained by quantitative sampling and rearing of caterpillars from the alien host Spathodea campanulata (Bignoniaceae). It examines the variation in Lepidoptera community composition at six study sites distributed on three adjacent islands ranging in size from 30 to 865,000 km². Results Spathodea campanulata was colonized by 54 folivorous species of Lepidoptera. Most of them were generalists, feeding on > 1 native plant family. However, the three most abundant species representing 83% of all individuals (Acherontia lachesis, Hyblaea puera complex and Psilogramma menephron) were relatively host specific, feeding predominantly on a single native family that is not the Bignoniaceae. Most of the 23 species analysed in detail had a wide geographic distribution, including 13 species spanning the entire 1000‐km study transect. While the Lepidoptera in two New Guinea areas 280 km apart were similar to each other, there was a discontinuity in species composition between New Guinea and the smaller islands. However, no negative effect of small islands on species richness was detected. Main conclusions Spathodea campanulata was rapidly colonized by folivorous Lepidoptera communities with species richness and dominance structure indistinguishable from the assemblages feeding on native hosts, despite its phylogenetic isolation from the native vegetation. Although most species were generalists, the highest population densities were reached by relatively specialized species, similar to the communities on native hosts. The species turnover across distances from 10 to 1000 km was relatively low as most of the species had wide geographic ranges.     

The importance of sward architectural complexity in structuring predatory and phytophagous invertebrate assemblages

Abstract.  1. Although the importance of plant community assemblages in structuring invertebrate assemblages is well known, the role that architectural complexity plays is less well understood. In particular, direct empirical data for a range of invertebrate taxa showing how functional groups respond to plant architecture is largely absent from the literature.
2. The significance of sward architectural complexity in determining the species richness of predatory and phytophagous functional groups of spiders, beetles, and true bugs, sampled from 135 field margin plots over 2 years was tested. The present study compares the relative importance of sward architectural complexity to that of plant community assemblage.
3. Sward architectural complexity was found to be a determinant of species richness for all phytophagous and predatory functional groups. When individual species responses were investigated, 62.5% of the spider and beetle species, and 50.0% of the true bugs responded to sward architectural complexity.
4. Interactions between sward architectural complexity and plant community assemblage indicate that the number of invertebrate species supported by the plant community alone could be increased by modification of sward architecture. Management practices could therefore play a key role in diversifying the architectural structure of existing floral assemblages for the benefit of invertebrate assemblages.
5. The contrasting effects of sward architecture on invertebrate functional groups characterised by either direct (phytophagous species) or indirect (predatory species) dependence on plant communities is discussed. It is suggested that for phytophagous taxa, plant community assemblage alone is likely to be insufficient to ensure successful species colonisation or persistence without appropriate development of sward architecture.     

Application of an index of biological integrity (IBI) to fish assemblages of the rivers Khan and Kshipra (Madhya Pradesh), India

1. A multimetric index of fish assemblage integrity was developed and similarity analyses were conducted on fish species in two central Indian rivers and the effects of distance from municipal and industrial effluents on those indices then evaluated.
2. Five metrics from Karr et al . (1986 , Illinois Natural History Survey Special Publication 5 , Urbana, IL) were adopted: intolerant species richness, % omnivorous individuals, % top carnivore individuals, total number of individuals and % individuals with anomalies. Seven new metrics (native species richness, native family richness, benthic species richness, water column species richness, % non-native individuals, % tolerant individuals and % herbivorous individuals) were added.
3. Non-native individuals represented 1–55% of the assemblages at sampled sites which held fish.
4. Fish were present at eleven sites and not collected at two sites, despite heavy metal concentrations exceeding U.S. Environmental Protection Agency acute criteria at all sites.
5. Two types of metric scoring were examined. The traditional 5–3–1 method showed the same pattern as continuous scoring from 0 to 10, but produced a higher integrity class at one site.
6. Scores on our modified index of fish assemblage integrity increased with distance downstream from a major effluent source in each river. Jaccard similarity scores between the least disturbed downstream site and all other sites decreased with increasing distance and disturbance.
7. It was concluded that Karr's original index and its theoretical foundations are easily adaptable, even to an ichthyofauna containing no species, and only two families (Cyprinidae, Poeciliidae), in common with the midwestern United States.     

No tree an island: the plant–caterpillar food web of a secondary rain forest in New Guinea

We characterized a plant–caterpillar food web from secondary vegetation in a New Guinean rain forest that included 63 plant species (87.5% of the total basal area), 546 Lepidoptera species and 1679 trophic links between them. The strongest 14 associations involved 50% of all individual caterpillars while some links were extremely rare. A caterpillar randomly picked from the vegetation will, with ≥ 50% probability, (1) feed on one to three host plants (of the 63 studied), (2) feed on < 20% of local plant biomass and (3) have ≥ 90% of population concentrated on a single host plant species. Generalist species were quantitatively unimportant. Caterpillar assemblages on locally monotypic plant genera were distinct, while sympatric congeneric hosts shared many caterpillar species. The partitioning of the plant–caterpillar food web thus depends on the composition of the vegetation. In secondary forest the predominant plant genera were locally monotypic and supported locally isolated caterpillar assemblages.     

Host Plant Specialization and Species Turnover of Caterpillars Among Hosts in the Brazilian Cerrado

Decrease in the species composition similarity of herbivore assemblages with increasing phylogenetic distance between host plants is a widespread pattern. Here we used data for caterpillars in the Brazilian Cerrado to investigate how the similarity in caterpillar species composition decreases as the taxonomic level and genetic distance (GD) of their host plants increases. In addition, we elucidate the plant taxonomic level that provides the greatest contribution to turnover in the caterpillar species composition among host taxa. Adult Lepidoptera were reared from caterpillars collected from 52 plants over 13 yr in the same area, with each host plant sampled for 1 yr. Most species were specialists, with 66 percent of genus specialists among the nonsingleton species. The similarity in caterpillar species composition across plant taxa decreased from host species to genera, and from host genera to orders. Above this level, the similarity was consistently low. The GD between plants explained 82 percent of the variation in the similarity of caterpillar species composition. The contribution of caterpillar species turnover among host orders from the same superorder and among host superorders from the same subclass explained 70 percent of the caterpillar species richness as a whole. Our results lend support to the view that most tropical caterpillars are host specialists. Our findings further indicate that the number of orders and superorders of plants provide the greatest contribution to the total caterpillar richness compared with all of the other host taxonomic levels combined. Abstract in Portuguese is available at http://www.blackwell‐synergy.com/loi/btp .     

Species richness of phytophagous beetles in the tropical tree Brosimum utile (Moraceae): the effects of sampling strategy and the problem of tourists

Abstract.  1. Phytophagous beetles on six mature living trees and two dead trees of Brosimum utile (Moraceae) were surveyed during 1 year in a tropical wet forest in Panama. The dead trees were surveyed both as suspended in the canopy and after falling down to the understorey.
2. Canopy access was provided by a construction crane and sampling was performed by beating and hand-collecting. The same amount of time was spent on each tree in order to standardise sampling effort. A list of all species associated with the tree is presented.
3. A total of 3009 individuals representing 364 species were collected. Tourists were excluded from the analyses by recording host associations directly and by probability assessments of host associations based on abundance categories. A total of 2603 individuals and 244 species were associated with the tree. The proportion of tourists in the trees increased with sample size.
4. A single mature living tree had on average 58.5 ± 6.5 species. The local species richness of B. utile was estimated as 2.5 times higher than in a single mature tree; however, a substantial increase in species richness was attained when dead wood habitats were included. Saproxylic species made up 82% of the total material.
5. The investigated habitat types of B. utile constituted distinct, complementary species assemblages. Similarity between saproxylic species of dead suspended wood and dead understorey wood of the same tree was 0.2 (Morisita–Horn index), confirming a prominent vertical stratification among this guild.     

Impact of avian and arthropod predation on lepidopteran caterpillar densities and plant productivity in an ephemeral agroecosystem

Abstract.  1. Most studies evaluating the combined impact of spiders and other predators on herbivore densities in agroecosystems have focused primarily on their trophic connections with invertebrate predators (e.g. carabids, chrysopids); however linkages among spiders and vertebrate predators may also help structure the population dynamics of insect herbivores. A field experiment was conducted to examine the impact of avian and spider predation on lepidopteran caterpillar densities and plant productivity within a Brassica agroecosystem.
2. Arthropod abundance, leaf-chewing damage, and final plant productivity associated with broccoli, Brassica oleracea L. (var. italica ), were recorded for four treatments: (1) bird present but spiders removed; (2) both birds and spiders present; (3) birds excluded, spiders present; and (4) birds and spiders both excluded.
3. Densities of Artogeia rapae L. (Lepidoptera: Pieridae) and Trichoplusia ni Hübner (Lepidoptera: Noctuidae) large caterpillars and post feeding stages were reduced significantly by bird predation. The abundance of large caterpillars was also reduced on spider-inhabited plants during early plant growth; however the assemblage of birds and spiders did not suppress caterpillar densities more significantly than either predator alone.
4. Plants protected by birds, spiders, and birds plus spiders sustained less folivory attributable to leaf chewing caterpillars than check plants. Plant productivity was also greater for predator-protected plants than check plants.
5. Although spiders and parasitoids were responsible for some of the mortality inflicted upon lepidopteran caterpillars, it was concluded that in this study system, birds are the most important natural enemies of folivores.     

High local species richness of parasitic wasps (Hymenoptera: Ichneumonidae; Pimplinae and Rhyssinae) from the lowland rainforests of Peruvian Amazonia

Abstract.  1. The parasitic wasp family Ichneumonidae (Hymenoptera) is of great interest because it has been claimed that its species richness does not increase with decreasing latitude.
2. No extensive studies of the family have been conducted in South American localities.
3. Arthropods were sampled using 27 Malaise traps in the Allpahuayo–Mishana National Reserve (56 000 ha) in the north-eastern Peruvian Amazonian lowland rainforest. The total duration of the sampling programme was 185 Malaise trap months.
4. Altogether, 88 species were collected. This is one of the highest local pimpline and rhyssine species numbers ever recorded. A comparison with results from Mesoamerica revealed that at equal numbers of individuals sampled, the number of Pimplinae and Rhyssinae species in Peruvian Amazonia is at least twofold compared with lowland locations in Mesoamerica and somewhat higher than in the most species-rich Costa Rican higher altitude localities.
5. Non-parametric methods of estimating species richness were applied. These suggest that additional sampling would yield a considerable number of new Pimplinae and/or Rhyssinae species.     

Effects of catchment perturbations by logging and wildfires on zooplankton species richness and composition in Boreal Shield lakes

SUMMARY 1. Forest logging and wildfires are important perturbations of the boreal forest, but their effects on lake biota remain largely unknown. Here, we test whether zooplankton species richness and species assemblages differed among three groups of lakes in Eastern Canada characterised by different catchment conditions: logged in 1995 ( n =9); burnt in 1995 ( n =9); unperturbed ( n =20). Lakes were sampled in June, July and September 1 year after catchment perturbations.
2. Cumulative species richness in reference lakes averaged 46 (33–60) of which 63% were rotifers. Mean cumulative species richness and mean diversity in logged and burnt lakes did not differ from those in reference lakes.
3. Lake species assemblages were described by the density of 62 species (41 rotifers and 21 crustaceans). Among-group differences in species assemblages were not significant. Eighteen per cent of the total variability in species assemblages could be explained by 13 environmental factors, among which dissolved oxygen concentration and cyanobacteria biovolume were the most important. About 5% of species assemblage variability was attributed to covariation between environmental factors and time of sampling, while 4.1% was attributed to temporal variation.
4. Variations in zooplankton species richness and assemblages in Boreal Shield lakes are important, both among lakes and among sampling dates. They seem to depend on environmental factors unrelated to catchment-based perturbations, at least on the short-term of 1 year.     

Environmental gradients shift the direction of the relationship between native and alien plant species richness

Aim

To assess how environmental, biotic and anthropogenic factors shape native–alien plant species richness relationships across a heterogeneous landscape.

Location

Banks Peninsula, New Zealand.

Methods

We integrated a comprehensive floristic survey of over 1200 systematically located 6 × 6 m plots, with corresponding climate, environmental and anthropogenic data. General linear models examined variation in native and alien plant species richness across the entire landscape, between native‐ and alien‐dominated plots, and within separate elevational bands.

Results

Across all plots, there was a significant negative correlation between native and alien species richness, but this relationship differed within subsets of the data: the correlation was positive in alien‐dominated plots but negative in native‐dominated plots. Within separate elevational bands, native and alien species richness were positively correlated at lower elevations, but negatively correlated at higher elevations. Alien species richness tended to be high across the elevation gradient but peaked in warmer, mid‐ to low‐elevation sites, while native species richness increased linearly with elevation. The negative relationship between native and alien species richness in native‐dominated communities reflected a land‐use gradient with low native and high alien richness in more heavily modified native‐dominated vegetation. In contrast, native and alien richness were positively correlated in very heavily modified alien‐dominated plots, most likely due to covariation along a gradient of management intensity.

Main conclusions

Both positive and negative native–alien richness relationships can occur across the same landscape, depending on the plant community and the underlying human and environmental gradients examined. Human habitat modification, which is often confounded with environmental variation, can result in high alien and low native species richness in areas still dominated by native species. In the most heavily human modified areas, dominated by alien species, both native and alien species may be responding to similar underlying gradients.

     

Biological invasion into the nested assemblage of tree–beetle associations on the oceanic Ogasawara Islands

Invasion by alien organisms is a common worldwide phenomenon, and many alien species invade native communities. Invasion by alien species is especially likely to occur on oceanic islands. To determine how alien species become integrated into island plant–insect associations, we analyzed the structure of tree–beetle associations using host plant records for larval feeding by wood-feeding beetles (Coleoptera: Cerambycidae) on the oceanic Ogasawara Islands in the northwestern Pacific Ocean. The host plant records comprised 109 associations among 28 tree (including 8 alien) and 26 cerambycid (including 5 alien) species. Of these associations, 41.3% involved at least one alien species. Most native cerambycid species feed on host trees that have recently died. Alien trees were used by as many native cerambycid species (but by significantly more alien cerambycid species) as were native trees. Native cerambycid species used as many alien tree species (but significantly more native tree species) as did alien cerambycids. Thus, we observed many types of interactions among native and alien species. A network analysis revealed a significant nested structure in tree–cerambycid associations regardless of whether alien species were excluded from the analysis. The original nested associations on the Ogasawara Islands may thus have accepted alien species.     

Species pool size and invasibility of island communities: a null model of sampling effects

The success of alien species on oceanic islands is considered to be one of the classic observed patterns in ecology. Explanations for this pattern are based on lower species richness on islands and the lower resistance of species‐poor communities to invaders, but this argument needs re‐examination. The important difference between islands and mainland is in the size of species pools, not in local species richness; invasibility of islands should therefore be addressed in terms of differences in species pools. Here I examine whether differences in species pools can affect invasibility in a lottery model with pools of identical native and exotic species. While in a neutral model with all species identical, invasibility does not depend on the species pool, a model with non‐zero variation in population growth rates predicts higher invasibility of communities of smaller pools. This is because of species sampling; drawing species from larger pools increases the probability that an assemblage will include fast growing species. Such assemblages are more likely to exclude random invaders. This constitutes a mechanism through which smaller species pools (such as those of isolated islands) can directly underlie differences in invasibility.     

Differences in composition of macroinvertebrate communities with invasive and native Gammarus spp. (Crustacea: Amphipoda)

SUMMARY 1. Assessing the effects on communities of invasive species is often confounded by environmental factors. In Irish rivers, the introduced amphipod Gammarus pulex replaces the native G. duebeni celticus in lowland stretches. The two amphipods are associated with different macroinvertebrate communities, which may in part be the result of natural longitudinal physicochemical change. However, this hinders assessment of any direct community impacts of the invasive as compared with the native species. Here, we report on a fortuitous circumstance that allowed us to uncouple the community effects of Gammarus species from environmental differences.
2. The lowland stretch of the River Lissan is dissected by a weir, which has slowed the upstream invasion by G. pulex . We took physicochemical measurements and macroinvertebrate samples from three contiguous 150 m reaches of this stretch with G. pulex only, mixed Gammarus and G. d. celticus only communities.
3. We found no biologically significant differences in physicochemistry among the three reaches. Overall invertebrate densities did not differ among reaches. However, G. pulex numerically dominated its reach, whilst G. d. celticus abundance was relatively low in its reach. The G. pulex reach had significantly higher overall biomass because of high invader abundance. In addition, both diversity and species richness of macroinvertebrate communities were lower in the G. pulex than the G. d. celticus reach, with the mixed Gammarus reach intermediate.
4. Ordination indicated distinctly different associations of invertebrate community samples and taxa that were best explained by the distributions of the Gammarus species. Again, the mixed Gammarus species samples were intermediate.
5. This study indicates that the invasive G. pulex has a greater impact on macroinvertebrate community composition than the native G. d. celticus , probably through biotic interactions such as predation.     

Seasonal fluctuation, phenology and turnover of chafer assemblages – insight to the structural plasticity of insect communities in tropical farmlands

1 Studies on chafer assemblages were conducted on two farmland sites in the Terai lowland of Nepal (200 m above sea level) using light traps. During the course of a 2-year field monitoring program, a total of 4503 specimens was captured and an unexpectedly high number of syntopically co-occurring species was found: 52 from Gunganagar (GN) and 36 from Gaindakot (GK), respectively. Highest species abundances and species numbers were found during April and May.
2 Species occurrence was strongly correlated with air temperature and the maximum soil temperature, at least during the pre-monsoon season. However, assemblage structure from the two sites showed significant qualitative and quantitative changes seasonally, as well as from 1 year to the next. Turnover rates between adjacent months were in the range 26–62% (GN) and 37–70% (GK), whereas the turnover from 2004 to 2005 was 25.8% (GN) and 21.4% (GK) respectively.
3 When only dominant and subdominant taxa are considered, the seasonal change in species composition was even more striking.
4 Strong fluctuation in chafer assemblage over time suggests: (i) a possible influence of patchy habitat types and soil working on seasonal assemblage structure and (ii) colonization of suitable habitats (fields) in great part by chance.     

Elevational diversity patterns of small mammals on Mount Kinabalu, Sabah, Malaysia

1 Diversity patterns of small mammals were studied along an elevational transect on Mount Kinabalu, the highest mountain in South‐east Asia, utilizing data from previously existing sources and a new field study. A mark‐and‐release study (conducted during wet and dry seasons between November 1994 and April 1995) resulted in captures of 12 small mammal species, including two species of squirrels, two tree shrews, seven murid rodents and one gymnure. 2 Based on data compiled from this survey, museum specimens, and published and unpublished literature (analysed by locally weighted sums of squares and quadratic polynomial regressions), species richness of small mammals formed a middle elevation bulge, highest at about 1200–1400 m and declining at lower and higher elevations. Trapping during two seasons did not change the assessment of the pattern. 3 A cluster analysis of these data indicated that there are two elevationally associated faunas, one in the highlands and another in the lowlands. The transition between these two assemblages is at 1700–1800 m elevation. The lowland faunal assemblage has the highest number of species, with maximum species richness at about 1300 m for total small mammal species, about 1200 m for arboreal species and about 1400 m for terrestrial species. 4 The areas where much overlapping of species occurs are the elevations where climate and vegetation change rapidly from lowland to montane types. Tree species, gymnosperms, orchids and ferns showed a similar curvilinear pattern along the same elevational gradient, with maximum species richness at about 1400–1500 m. Temperature declined progressively with increasing elevation, but rainfall and humidity reached their highest levels at about 1700 m. 5 Maximum diversity of small mammals thus occurred at the elevation where a highland and a lowland assemblage overlapped, where several types of plants reached their maximum diversity, and where rainfall and humidity reached their maxima. Similar patterns have been documented for small mammals, plants, and climate at sites scattered in Indo‐Australia from Taiwan to New Guinea.     

Asymmetrical competition between Neotropical dung beetles and its consequences for assemblage structure

Abstract.  1. This study combines the results of laboratory experiments using representative assemblage components and pitfall trapping over a large geographical area to examine the hypothesis that ongoing interspecific competition structures Neotropical dung beetle assemblages.
2. From Guatemala to Panama assemblages of large to medium-sized, fast-tunnelling dung beetles include a single large, nocturnal dichotomiine species, Dichotomius annae (Kohlmann & Solís, 1997). In competition experiments, this species out-competed the medium-sized coprine species, Copris lugubris Boheman and Phanaeus demon Laporte-Castelnau, for dung and nesting space, in spite of earlier colonisation by the diurnal species, P. demon .
3. Differences in the abundance of D. annae at Central American sites did not affect total fast-tunnelling dung beetle assemblage richness over the rainy season. However, D. annae rank order was directly related to the probability of interspecific encounters (Hurlbert's Δ ₁) among species. These trends were also observed when species lists from published and unpublished studies of other large allopatric dichotomiine species, with a more northerly distribution, were included in the analyses.
4. The results obtained suggest that where large dichotomiine species are abundant, their efficient pre-emption of a considerable proportion of available resources drives all, or most, other fast-tunnelling species to a lower population density, thereby decreasing assemblage diversity.