Predation by odonates depresses mosquito abundance in water-filled tree holes in Panama

In the lowland moist forest of Barro Colorado Island (BCI), Panama, larvae of four common species of odonates, a mosquito, and a tadpole are the major predators in water-filled tree holes. Mosquito larvae are their most common prey. Holes colonized naturally by predators and prey had lower densities of mosquitoes if odonates were present than if they were absent. Using artificial tree holes placed in the field, we tested the effects of odonates on their mosquito prey while controlling for the quantity and species of predator, hole volume, and nutrient input. In large and small holes with low nutrient input, odonates depressed the number of mosquitoes present and the number that survived to pupation. Increasing nutrient input (and consequently, mosquito abundance) to abnormally high levels dampened the effect of predation when odonates were relatively small. However, the predators grew faster with higher nutrients, and large larvae in all three genera reduced the number of mosquitoes surviving to pupation, even though the abundance of mosquito larvae remained high. Size-selective predation by the odonates is a likely explanation for this result; large mosquito larvae were less abundant in the predator treatment than in the controls. Because species assemblages were similar between natural and artificial tree holes, our results suggest that odonates are keystone species in tree holes on BCI, where they are the most common large predators. Received: 4 November 1996 / Accepted: 11 April 1997     

Effects of leaf litter species on macroinvertebrate community properties and mosquito yield in Neotropical tree hole microcosms

Detritus quality and quantity affect macroinvertebrate productivity and distribution in many freshwater ecosystems. This study experimentally investigated the effects of leaf litter from Ceiba pentandra, Dipteryx panamensis, Ficus yoponensis, and Platypodium elegans on macroinvertebrate species composition, richness, and abundance in artificial water-filled tree holes in a lowland moist forest of Panama. Species composition was similar among treatments, but species richness and longevity differed among litter types and were consistently highest with Platypodium litter. Similar patterns were observed in natural tree holes of the focal tree species. The mosquito Culex mollis was the most abundant species in the field experiment. Average conductivity and dissolved oxygen concentration differed among leaf species, but pH did not. Leaf toughness was positively correlated with mean macroinvertebrate abundance and cumulative species richness. A laboratory experiment measured C. mollis yield and pupation time in tree hole microcosms containing the four litter species. Cumulative mosquito mass and time to pupation differed among leaf litter species, with Platypodium litter supporting the greatest yield. Pupation was slowest on Ceiba litter. Grazing by mosquito larvae facilitated leaf decomposition in all treatments. Results suggest that differences in macroinvertebrate species richness and mosquito yield can be attributed to differences in nutritional quality among litter species. Received: 14 October 1998 / Accepted: 21 February 1999     

The meiofauna of artificial water-filled tree holes: colonization and bottom-up effects

The meiofaunal community of artificial water-filled tree holes was determined, and the bottom-up effects of different amounts of leaf litter on abundance and diversity were estimated. We assume a positive impact of leaf litter on meiofaunal abundances, species diversity, and trophic links. Plastic cups with different amounts of leaf litter were placed in a beech forest (Teutoburg Forest, Bielefeld, Germany) for 24 weeks. As early as 1 week later, the artificial tree holes were colonized by bdelloid rotifers, tardigrades, and nematodes. Rotifers were dominant throughout the experiment, followed by nematodes and tardigrades. The 29 nematode species that were identified included bacterial and hyphal feeders, with common species such as Plectus cirratus/accuminatus and Aphelenchoides parietinus predominating. Impacts of water volume (up to complete desiccation), pH, and O₂ on the meiofaunal community were not detected, whereas the addition of leaf litter resulted in bottom-up effects. Nematode abundance, especially that of bacterial feeders, and species number increased with increasing leaf input. The predatory nematode Prionchulus muscorum was found only in treatments containing high leaf content. Rotifer abundances were partly negatively affected by the amount of added leaves and, like tardigrades, showed a reversal in their correlation at higher leaf inputs. Our study revealed the fast colonization of small water bodies by meiofaunal organisms and the importance of passively distribution. Furthermore, the results provide a comparison with the meiofaunal community in lakes and soil.     

Resource–consumer diversity: testing the effects of leaf litter species diversity on stream macroinvertebrate communities

1. Understanding relationships between resource and consumer diversity is essential to predicting how changes in resource diversity might affect several trophic levels and overall ecosystem functioning. 2. We tested for the effects of leaf litter species diversity (i.e. litter mixing) on litter mass remaining and macroinvertebrate communities (taxon diversity, abundance and biomass) during breakdown in a detritus‐based headwater stream (North Carolina, U.S.A.). We used full‐factorial analyses of single‐ and mixed‐species litter from dominant riparian tree species with distinct leaf chemistries [red maple (Acer rubrum), tulip poplar (Liriodendron tulipifera), chestnut oak (Quercus prinus) and rhododendron (Rhododendron maximum)] to test for additivity (single‐species litter presence/absence effects) and non‐additivity (emergent effects of litter species interactions). 3. Significant non‐additive effects of litter mixing on litter mass remaining were explained by species composition, but not richness, and litter‐mixing effects were variable throughout breakdown. Specifically, small differences in observed versus expected litter mass remaining were measured on day 14; whereas observed litter mass remaining in mixed‐species leaf packs was significantly higher on day 70 and lower on day 118 than expected from data for single‐species leaf packs. 4. Litter mixing had non‐additive effects on macroinvertebrate community structure. The number of species in litter mixtures (two to four), but not litter species composition, was a significant predictor of the dominance of particular macroinvertebrates (i.e. indicator taxa) within mixed‐species packs. 5. In addition, the presence/absence of high‐ (L. tulipifera) and low‐quality (R. maximum) litter had additive effects on macroinvertebrate taxon richness, abundance and biomass. The presence of L. tulipifera litter had both positive (synergistic) and negative (antagonistic) effects on invertebrate taxon richness, that varied during breakdown but were not related to litter chemistry. In contrast, the presence/absence of L. tulipifera had a negative relationship with total macroinvertebrate biomass (due to low leaf mass remaining when L. tulipifera was present and higher condensed and hydrolysable tannins associated with leaf packs lacking L. tulipifera). Macroinvertebrate abundance was consistently lower when R. maximum was present, which was partially explained by litter chemistry [e.g., high concentrations of lignin, condensed tannins, hydrolysable tannins and total phenolics and high carbon to nutrient (N and P) ratios]. 6. The bottom‐up effects of litter species diversity on stream macroinvertebrates and litter breakdown are different, which suggests that structural attributes of macroinvertebrate communities may only partially explain the effects of litter‐mixing on organic matter processing in streams. In addition, stream macroinvertebrates colonising decomposing litter are influenced by resource diversity as well as resource availability. Broad‐scale shifts in riparian tree species composition will alter litter inputs to streams, and our results suggest that changes in the diversity and availability of terrestrial litter may alter stream food webs and organic matter processing.     

The influence of nest availability on the abundance and diversity of twig-dwelling ants in a Papua New Guinea forest

Tropical ant communities are frequently diverse, but highly patchy in nature. The availability of suitable nest sites may be a regulating force in structuring litter ant communities. Our aim was to examine ant resource utilization in naturally occurring twigs, and to modify the availability of these resources in order to quantify the influence of nest availability on ant communities in a Papua New Guinean forest. First, we compared ant communities that assemble in artificial twigs (drilled, wooden dowels), naturally occurring twigs, and the leaf litter. A total of 55 ant species were captured: 33 from the leaf litter, 29 from naturally occurring twigs, and only 12 from artificial nests. Significantly different communities formed in each of the three nest types. Second, we examined how the density of natural or artificial nest material influenced the ant abundance and species richness. Plots had between 5 and 96 potential nest sites. An average of only 11.2% of these twigs was colonized. Both species richness and the total abundance of adult ants were significantly positively correlated with increasing naturally occurring twig density. Conversely, increasing the availability of artificial nests from 5 to 20 per plot had no significant effect on the proportion of artificial nests colonized, species richness, or the colony size. We observed that ant species richness and abundance increased with natural twig density, at least for naturally occurring communities. But why so many twigs remain vacant and available for ant colonization remains unknown. Other biotic and abiotic factors likely influence the use of nesting habitat in these ant communities.     

Effect of leaf litter and density on fitness and population performance of the hole mosquito Aedes triseriatus

Abstract.

• 1 We tested the effects of food, in the form of leaf litter, and density on population growth and fitness correlates of the tree hole mosquito Aedes triseriatus. Our field experiment used a 2 x 2 randomized block design, with three holes as blocks. In cages within three holes, we manipulated densities of Aedes triseriatus larvae, and presence of leaf litter. Our laboratory experiment used a 2 x 3 factorial design in which we also manipulated densities of larvae and availability of leaf litter within similar cages (inside, outside, or absent). For both experiments we determined effects on survival, days to and mass at eclosion of both sexes, and a composite index of population performance λ′, that estimates finite rate of increase.
• 2 In the field experiment, we found significant and large effects of leaf litter and of density on the performance of A. triseriatus. The effect of density did not depend on leaf litter availability. We documented significant variation among tree holes for most correlates of fitness. Often, the effects of treatments varied significantly depending on the tree hole tested.
• 3 In the laboratory experiment we found significant effects of density and litter, and that direct browsing on leaf litter is necessary for the effect of litter on performance of A. triseriatus. In the laboratory, the negative effect of increased density was dependent on leaf litter availability.
• 4 Our results demonstrate that leaf litter has important effects on population performance of tree hole mosquitoes in natural tree holes. Direct browsing on the surface of leaf litter is the most likely mechanism by which litter enhances population growth. The impact of litter on populations varies among tree holes.

     

Aggregation of Cricket Activity in Response to Resource Addition Increases Local Diversity

Crickets are often found feeding on fallen fruits among forest litter. Fruits and other sugar-rich resources are not homogeneously distributed, nor are they always available. We therefore expect that crickets dwelling in forest litter have a limited supply of sugar-rich resource, and will perceive this and displace towards resource-supplemented sites. Here we evaluate how sugar availability affects cricket species richness and abundance in old-growth Atlantic forest by spraying sugarcane syrup on leaf litter, simulating increasing availability, and collecting crickets via pitfall trapping. We found an asymptotic positive association between resource addition and species richness, and an interaction between resource addition and species identity on cricket abundance, which indicates differential effects of resource addition among cricket species. Our results indicate that 12 of the 13 cricket species present in forest litter are maintained at low densities by resource scarcity; this highlights sugar-rich resource as a short-term driver of litter cricket community structure in tropical forests. When resource was experimentally increased, species richness increased due to behavioral displacement. We present evidence that the density of many species is limited by resource scarcity and, when resources are added, behavioral displacement promotes increased species packing and alters species composition. Further, our findings have technical applicability for increasing sampling efficiency of local cricket diversity in studies aiming to estimate species richness, but with no regard to local environmental drivers or species-abundance characteristics.     

Interactive effects of pH and leaf litter on a shredder, the scirtid beetle, Helodes pulchella, inhabiting tree-holes

1. Scirtid beetles (Coleoptera: Scirtidae) are common inhabitants of water-filled treeholes and interact with other detritivores in a processing chain commensalism. The strength of the commensalism is determined by resource quantity and the organisms involved have different tolerances to low pH. To determine the effects and interactions of resource quantity and pH on one of these leaf-shredding scirtid beetles, Helodes pulchella (Guerin), leaf litter and pH were varied independently in experimental microcosms which mimic treehole habitats.
2. Helodes pulchella growth was affected by both resources and pH in two similar experiments conducted in different years. Scirtid larvae grew more slowly in low resource treatments and also grew more slowly in low pH treatments. Scirtid survival was not affected by pH, but was lower in high resource microcosms in the 1997 experiment. Consumption of leaf litter was much higher in high resource microcosms, even though not all leaf litter was consumed in low leaf litter treatments.
3. Thus, water chemistry and leaf litter quantity could have strong effects on resource availability through effects on these beetle facilitators, in turn affecting other insects living in these detritus-based communities.     

Concurrent effects of resource pulse amount, type, and frequency on community and population properties of consumers in detritus-based systems

Episodic resource inputs (i.e., pulses) can affect food web properties and community dynamics, but detailed mechanistic understanding of such effects remain elusive. Natural aquatic microsystems (e.g., tree holes, human-made containers) are colonized by invertebrates that form complex food webs dependent on episodic and sometimes sizeable inputs of allochthonous detritus from adjacent terrestrial environments. We investigated how variation in pulse frequency, amount, and resource type interacted to affect richness, abundance, composition, and population sizes of colonizing invertebrates in water-filled tires and tree hole analogs in a forest habitat. Different container types were used to assess the generality of effects across two environmental contexts. Containers received large infrequent or small frequent pulses of animal or leaf detritus of different cumulative amounts distributed over the same period. Invertebrates were sampled in June and September when cumulative detritus input was equal for the two pulse frequencies. Pulse frequency and detritus type interacted to affect the responses of richness and abundance in both months; pulse frequency alone in June affected the relationship between richness and abundance. Richness and abundance were also greater with more detritus regardless of detritus type. One group, the filter feeders, were most important in driving the response of abundance and richness to pulses, especially in June. This work highlights the potential complex nature of responses of communities and populations to resource pulses and implicates the ability of certain groups to exploit pulses of detrital resources as a key to understanding community-level responses to pulses.     

Organization of predator assemblages in Neotropical tree holes: effects of abiotic factors and priority

Abstract. 1. Water-filled tree holes in a lowland forest in Panama harbour an assemblage of large predators consisting of the larvae of five common species of Odonata, the mosquito Toxorhynchites theobaldi, and tadpoles of Dendrobates auratus. Odonate females oviposit in both large and small tree holes. However, the three largest species emerge from larger tree holes, on average, than do the two smallest species. Can assembly rules explain this and other patterns of predator distribution? 2. Past experiments suggested that fast growth of the largest, but later-colonizing odonates enabled them to out-compete the smaller, slower-growing Mecistogaster in large holes. In small holes, however, the first predator, regardless of species, should presumably kill any later arrivals. Priority effects in small holes were tested for their consistency across predator species. Two alternative explanations for differential odonate survivorship were also tested: abiotic conditions and the effect of non-odonate predators. 3. Diurnal fluctuations in oxygen content, pH, and temperature within holes were as great as the variation found between large and small tree holes; abiotic conditions were poor predictors of species occupancy. 4. Exchanging the largest and smallest odonate species from their original holes did not affect survivorship, suggesting that the observed patterns of emergence are unlikely to result from differential tolerance to abiotic factors that were not measured. 5. When larger and smaller predators were paired in 400-ml pots and provided with alternative prey, typically only the larger predator survived, regardless of species. The exception was T. theobaldi, which was often killed by odonates and tadpoles smaller than itself. 6. Between May and July, the occurrence of Mecistogaster in large tree holes declined, before larvae could have emerged. Neither abiotic effects nor differential predation by non-odonates could explain this habitat-specific decrease in survivorship. This temporal pattern is most consistent with the previous conclusion that in large holes, Mecistogaster suffer intraguild predation from later-colonizing, but faster-growing Megaloprepus and aeshnids. Whereas Mecistogaster can pre-empt guild members from small tree holes, they cannot do so in large holes where predators with fast initial growth realize a competitive advantage.     

乔木根系和凋落物对南亚热带3种人工林土壤线虫群落的差异化影响

根系分泌物和凋落物为土壤食物网提供了基础的养分资源。然而,不同树种纯林和混交林地下根系和地上凋落物对土壤线虫群落的影响机制尚不清楚。2019年9月在广西凭祥热带林业实验中心选取格木(Erythrophleum fordii Oliv.)纯林、马尾松(Pinus massoniana Lamb.)纯林和格木×马尾松混交林3种林分类型,分别设置对照、阻断乔木根系、去除地上凋落物和阻断乔木根系并去除地上凋落物四组实验处理,于2021年3月对3种林分类型不同处理下的土壤线虫群落和土壤理化性质进行了调查。研究结果表明,无论哪种林分类型,阻断根系改变了土壤线虫群落的营养类群组成,显著降低了食真菌线虫相对多度,增加了植物寄生线虫相对多度;去除凋落物显著降低了土壤线虫密度、类群数、线虫通路比值和结构指数,增加了基础指数,表明去除凋落物降低了土壤食物网的稳定性。无论哪种林分类型,人工林中树木地下根系输入是构建土壤线虫群落营养类群组成的主要驱动因素,地上凋落物在维持土壤食物网稳定性方面发挥着重要的作用。此外,阻断根系和去除凋落物对混交林中土壤线虫群落没有显著的影响,表明含固氮树种的格木×马尾松混交林比人工...     

Impact of habitat structure and fruit abundance on avian seed dispersal and fruit predation

So far, it is poorly understood how differential responses of avian seed dispersers and fruit predators to changes in habitat structure and fruit abundance along land-use gradients may translate into consequences for the seed dispersal of associated plants. We selected a gradient of habitat modification (forest, semi-natural, and rural habitat) characterized by decreasing tree cover and a high variation in local fruit availability. Along this gradient we quantified fruit removal by avian seed dispersers and fruit predators from 18 Sorbus aucuparia trees. We analyzed the relative importance of tree cover and fruit abundance in explaining species richness, abundance and fruit removal rates of both guilds from S. aucuparia trees. Species richness and abundance of seed dispersers decreased with decreasing tree cover, whereas fruit removal by seed dispersers decreased with decreasing fruit abundance independent of tree cover. Both variables had no effect on species richness, abundance and fruit removal by fruit predators. Consequently, seed dispersers dominated relative fruit removal in fruit-rich sites but the dispersal/predation ratio shifted in favor of predation in fruit-poor habitat patches. Our study demonstrates that variation in local habitat structure and fruit abundance can cause guild-specific responses. Such responses may result in a shift in fruit removal regimes and might affect the dispersal ability of dependent fruiting plants. Future studies should aim at possible consequences for plant recruitment and guild-specific responses of frugivores to disturbance gradients on the level of entire plant–frugivore associations.     

Bamboo dominance reduces tree regeneration in a disturbed tropical forest

Human disturbance may change dominance hierarchies of plant communities, and may cause substantial changes in biotic environmental conditions if the new dominant species have properties that differ from the previous dominant species. We examined the effects of bamboos (Bambusa tulda and Cephalostachyum pergracile) and their litter on the overall woody seedling abundance, species richness and diversity in a mixed deciduous forest in northeastern Thailand. These bamboo species are gaining dominance after human disturbance. Our results show that seedling abundance and species richness were reduced by bamboo canopies. Seedling abundance and species diversity under bamboo canopies were affected by bamboo litter, whereas seedling abundance and species diversity outside bamboo canopies did not respond to the mixed-tree litter manipulation. Removal of bamboo litter increased seedling abundance and species diversity. However, bamboo litter addition did not affect seedling abundance or species diversity compared to either control or litter removal. This may indicate that the effect of natural amount of bamboo litter is as high as for litter addition in preventing seedling establishment by woody species and hence in minimizing resource competition. We conclude that undergrowth bamboos and their litter affect tree seedling regeneration differently from mixed-tree litter, causing changes in plant community composition and species diversity. Increased human disturbance, causing a shift in dominance structure of these forests, may result in a concomitant reduction in their overall woody species abundance, richness and diversity. Thus, management of bamboos by controlling their distribution in areas of high bamboo density can be an important forest restoration method.     

Trees as templates for tropical litter arthropod diversity

Increased tree species diversity in the tropics is associated with even greater herbivore diversity, but few tests of tree effects on litter arthropod diversity exist. We studied whether tree species influence patchiness in diversity and abundance of three common soil arthropod taxa (ants, gamasid mites, and oribatid mites) in a Panama forest. The tree specialization hypothesis proposes that tree-driven habitat heterogeneity maintains litter arthropod diversity. We tested whether tree species differed in resource quality and quantity of their leaf litter and whether more heterogeneous litter supports more arthropod species. Alternatively, the abundance–extinction hypothesis states that arthropod diversity increases with arthropod abundance, which in turn tracks resource quantity (e.g., litter depth). We found little support for the hypothesis that tropical trees are templates for litter arthropod diversity. Ten tree species differed in litter depth, chemistry, and structural variability. However, the extent of specialization of invertebrates on particular tree taxa was low and the more heterogeneous litter between trees failed to support higher arthropod diversity. Furthermore, arthropod diversity did not track abundance or litter depth. The lack of association between tree species and litter arthropods suggests that factors other than tree species diversity may better explain the high arthropod diversity in tropical forests.     

Plant-mediated indirect effects of carpenterworms on the insect communities attracted to fermented tree sap

Carpenterworm (Lepidoptera, Cossidae) larvae bore into trunks of the oak Quercus acutissima, thereby promoting sap exudation, and prey on insects attracted to tree sap. We examined the interactions between carpenterworms and sap-attracted insects to elucidate community-level consequences of carpenterworms and to estimate the relative magnitudes of their direct and indirect effects on community structure. Species richness, total abundance, and Simpson’s index of diversity (1/D) in tree sap communities were all significantly higher in carpenterworm-associated patches (sap-exuding patches that contained either larvae or larval nests) than in patches without evidence of carpenterworms. Abundance was also significantly higher in carpenterworm-associated patches for 10 out of 14 taxonomic groups, and this difference was much greater in the following groups that are sensitive to resource increases: drosophilid flies (Drosophilidae), sap beetles (Nitidulidae), and rove beetles (Staphylinidae). These results indicate that carpenterworms increase community size indirectly by increasing resource abundance, which is supported by the results of structural equation modeling (SEM). SEM also revealed that the direct effect of carpenterworms on species richness was weaker than their indirect effect, suggesting that predation by carpenterworms does not determine community structure. Similarly, carpenterworms can increase the abundance of some taxa by increasing resource abundance, and the predation pressure from carpenterworms on most taxa may be minor. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The diversity of beetle assemblages in different habitat types in Sabah, Malaysia

The diversity of beetle assemblages in different habitat types (primary forest, logged forest, acacia plantation and oil palm plantation) in Sabah, Malaysia was investigated using three different methods based on habitat levels (Winkler sampling, flight-interception-trapping and mist-blowing). The overall diversity was extremely high, with 1711 species recorded from only 8028 individuals and 81 families (115 family and subfamily groups). Different degrees of environmental changes had varying effects on the beetle species richness and abundance, with oil palm plantation assemblage being most severely affected, followed by acacia plantation and then logged forest. A few species became numerically dominant in the oil palm plantation. In terms of beetle species composition, the acacia fauna showed much similarity with the logged forest fauna, and the oil palm fauna was very different from the rest. The effects of environmental variables (number of plant species, sapling and tree densities, amount of leaf litter, ground cover, canopy cover, soil pH and compaction) on the beetle assemblage were also investigated. Leaf litter correlated with species richness, abundance and composition of subterranean beetles. Plant species richness, tree and sapling densities correlated with species richness, abundance and composition of understorey beetles while ground cover correlated only with the species richness and abundance of these beetles. Canopy cover correlated only with arboreal beetles. In trophic structure, predators represented more than 40% of the species and individuals. Environmental changes affected the trophic structure with proportionally more herbivores (abundance) but fewer predators (species richness and abundance) in the oil palm plantation. Biodiversity, conservation and practical aspects of pest management were also highlighted in this study.     

Container-breeding mosquitoes and predator community dynamics along an urban-forest gradient: The effects of habitat type and isolation

Environmental disturbances such as deforestation, urbanization or pollution have been widely acknowledged to play a key role in the emergence of many infectious diseases, including mosquito-borne viruses. However, we have little understanding of how habitat isolation affects the communities containing disease vectors. Here, we test the effects of habitat type and isolation on the colonization rates, species richness and abundances of mosquitoes and their aquatic predators in water-filled containers in northwestern Thailand. For eight weeks water-filled containers were monitored in areas containing forest, urban and agricultural habitats and mixtures of these three. Mosquito larvae of the genera Aedes and Culex appeared to be differentially affected by the presence of the dominant predator; Toxorhynchites splendens (Culicidae). Therefore, a predation experiment was conducted to determine predator response to prey density and its relative effects on different mosquito prey populations. Colonization rates, species richness and abundances of mosquito predators were strongly related to forest habitat and to the distance from other aquatic habitats. Areas with more tree cover had higher predator species richness and abundance in containers. Containers that were close to surface water were more rapidly colonized than those further away. In all habitat types, including urban areas, when predators were present, the number of mosquito larvae was much lower. Containers in urban areas closer to water-bodies, or with more canopy cover, had higher predator colonization rates and species richness. T. splendens (Culicidae) preyed on the larvae of two mosquito genera at different rates, which appeared to be related to prey behaviour. This study shows that anthropogenic landscape modification has an important effect on the natural biological control of mosquitoes. Vector control programmes and urban planning should attempt to integrate ecological theory when developing strategies to reduce mosquito populations. This would result in management strategies that are beneficial for both public health and biodiversity.     

Laboratory studies of ant predation on parapatric reptile ticks

Abstract Two reptile tick species, Aponomma hydrosauri and Amblyomma limbatum, have a parapatric distribution in South Australia. Predation may play a role in maintaining the boundary. Laboratory colonies of Rhytidoponera and Iridomyrmex ants were collected from near Mt Mary, South Australia, close to the tick boundary. They were tested as predators of the two tick species. In the experiments, ticks in leaf litter were more protected from predation than those on bare soil. When comparing leaf litter types from the Mt Mary area, mallee litter was more protective than bluebush litter of equivalent depth. Ticks positioned at the base of the litter layer were more protected from predation than those at the litter surface, and Amb. limbatum ticks were more resistant to predation than Ap. hydrosauri ticks. These results contribute to our understanding of the mechanisms maintaining the abrupt parapatric boundary between the two tick species. Predators may contribute to preventing the more susceptible Ap. hydrosauri from spreading further north, where bluebush litter is more common, and so predation risk is higher. Predators probably have less influence in preventing Amb. limbatum from spreading further south.     

Aquatic islands in the sky: 100 years of research on water‐filled tree holes

Water‐filled tree holes are unique ecosystems that may occur high up in tree crowns and are essentially aquatic islands in the sky. Insect larvae, mesofauna, and other organisms colonize the waterbodies and feed on the accumulating detritus. Water‐filled tree holes are not only important habitats for these species but have been used as model systems in ecology. Here, we review more than 100 years of research on tree‐hole inhabiting organisms and show that most studies focus on selected or even single species (most of which are mosquitoes), whereas only few studies examine groups other than insects, especially in the tropics. Using a vote counting of results and a meta‐analysis of community studies, we show that the effects of tree‐hole size and resources on abundance and richness were investigated most frequently. Both were found to have a positive effect, but effect sizes were modulated by site‐specific environmental variables such as temperature or precipitation. We also show that parameters such as the height of the tree holes above ground, tree‐hole density, predation, and detritus type can be important drivers of organism abundance or richness but are less often tested. We identify several important research gaps and potential avenues for future research. Specifically, future studies should investigate the structure, functions, and temporal dynamics of tree‐hole food webs and their cross‐system interactions, for example, with terrestrial predators that act as a connection to their terrestrial surroundings in meta‐ecosystems. Global observational or experimental tree‐hole studies could contribute pivotal information on spatial variation of community structure and environmental drivers of community assembly. With a better understanding of these unique aquatic habitats in terrestrial ecosystems, natural and artificial tree holes can not only serve as model systems for addressing fundamental ecological questions but also serve as indicator systems of the impacts of environmental change on ecosystems.