Merlijn Jocque

Dominant predators mediate the impact of habitat size on trophic structure in bromeliad invertebrate communities

Local habitat size has been shown to influence colonization and extinction processes of species in patchy environments. However, species differ in body size, mobility, and trophic level, and may not respond in the same way to habitat size. Thus far, we have a limited understanding of how habitat size influences the structure of multitrophic communities and to what extent the effects may be generalizable over a broad geographic range. Here, we used water-filled bromeliads of different sizes as a natural model system to examine the effects of habitat size on the trophic structure of their inhabiting invertebrate communities. We collected composition and biomass data from 651 bromeliad communities from eight sites across Central and South America differing in environmental conditions, species pools, and the presence of large-bodied odonate predators. We found that trophic structure in the communities changed dramatically with changes in habitat (bromeliad) size. Detritivore : resource ratios showed a consistent negative relationship with habitat size across sites. In contrast, changes in predator: detritivore (prey) ratios depended on the presence of odonates as dominant predators in the regional pool. At sites without odonates, predator: detritivore biomass ratios decreased with increasing habitat size. At sites with odonates, we found odonates to be more frequently present in large than in small bromeliads, and predator: detritivore biomass ratios increased with increasing habitat size to the point where some trophic pyramids became inverted. Our results show that the distribution of biomass amongst food-web levels depends strongly on habitat size, largely irrespective of geographic differences in environmental conditions or detritivore species compositions. However, the presence of large-bodied predators in the regional species pool may fundamentally alter this relationship between habitat size and trophic structure. We conclude that taking into account the response and multitrophic effects of dominant, mobile species may be critical when predicting changes in community structure along a habitat-size gradient.

Toward a Global Phylogeny of the “Living Fossil" Crustacean Order of the Notostraca

Tadpole shrimp (Crustacea, Notostraca) are iconic inhabitants of temporary aquatic habitats worldwide. Often cited as prime examples of evolutionary stasis, surviving representatives closely resemble fossils older than 200 mya, suggestive of an ancient origin. Despite significant interest in the group as ‘living fossils’ the taxonomy of surviving taxa is still under debate and both the phylogenetic relationships among different lineages and the timing of diversification remain unclear. We constructed a molecular phylogeny of the Notostraca using model based phylogenetic methods. Our analyses supported the monophyly of the two genera Triops and Lepidurus, although for Triops support was weak. Results also revealed high levels of cryptic diversity as well as a peculiar biogeographic link between Australia and North America presumably mediated by historic long distance dispersal. We concluded that, although some present day tadpole shrimp species closely resemble fossil specimens as old as 250 mya, no molecular support was found for an ancient (pre) Mesozoic radiation. Instead, living tadpole shrimp are most likely the result of a relatively recent radiation in the Cenozoic era and close resemblances between recent and fossil taxa are probably the result of the highly conserved general morphology in this group and of homoplasy.

Anostracan monopolisation of early successional phases in temporary waters

The length of the hydrocycle restrains the development of communities in temporary aquatic habitats. Little information is available on the importance of biotic interactions in shaping the communities in these temporary habitats. A common observation in the freshwater rock pool community assembly process is the clearly separated density peaks over time of fairy shrimp (Anostraca) and cladocerans (Anomopoda). Fairy shrimp (Anostraca), the fl agship group and dominant fi lter feeders of temporary waters hatch early after inundation. This contrasts with the occurrence pattern of coexisting cladocerans, which despite higher chances of abortive hatching occur later during the hydroperiod. To study this apparent succession pattern and test the possible presence of a biotic interaction, we set up enclosure experiments in freshwater rock pools in Western Australia and monitored cladoceran (Macrothrix hardingii) densities in the presence of variable densities or absence of fairy shrimp (Branchinella longirostris). The anomopod cladoceran populations decreased with increasing anostracan densities revealing a negative biotic interaction. The competitive dominance of anostracans most probably was mainly due to exploitation competition, with possibly elements of interference competition or predation included. Early hatching and competitive superi- ority may help anostracans in temporary pools to monopolize the habitat with respect to small and/or other fi lter feeding invertebrates. As such they infl uence succession dynamics and invertebrate community structure, making anostracans keystone species of temporary pools.

Aquatic invertebrate communities in tank bromeliads:how well do classic ecological patterns apply?

Tank bromeliads (Bromeliaceae) often occur in high densities in the Neotropics and represent a key freshwater habitat in montane forests, housing quite complex invertebrate communities. We tested the extent to which there are species richness–altitude, richness–environment, richness–size, richness–habitat complexity and richness–isolation relationships for the aquatic invertebrate communities from 157 bromeliads in Cusuco National Park, Honduras. We found that invertebrate species richness and abundance correlated most strongly, and positively, with habitat size, which accounted for about a third of the variance in both. Apart from bromeliad size (equivalent of the species–area relationship), we found remarkably little evidence of classic biogeographic and ecological relationships with species richness in this system. Community composition correlated with altitude, bromeliad size and position, though less than 20% of the variation was accounted for by the tested variables. The turnover component of dissimilarity between the communities correlated with altitude, while the nestedness-resultant component was related to bromeliad size. The unexplained variance could reflect a large stochastic component in the system, associated with the ephemerality of the habitat patches (both the plants themselves and the fluctuations in their water content) and stochasticity due to the dispersal dynamics in the system. We conclude that there is a small contribution of classic biogeographic factors to the diversity and community composition of aquatic invertebrates communities in bromeliads. This may be due to the highly dynamic nature of this system, with small patch sizes and high emigration rates. The patterns may mostly be driven by factors affecting colonisation success.

Modelling hurricane exposure and wind speed on a mesoclimate scale: a case study from Cusuco NP, Honduras

High energy weather events are often expected to play a substantial role in biotic community dynamics and large scale diversity patterns but their contribution is hard to prove. Currently, observations are limited to the documentation of accidental records after the passing of such events. A more comprehensive approach is synthesising weather events in a location over a long time period, ideally at a high spatial resolution and on a large geographic scale. We provide a detailed overview on how to generate hurricane exposure data at a meso-climate level for a specific region. As a case study we modelled landscape hurricane exposure in Cusuco National Park (CNP), Honduras with a resolution of 50 m×50 m patches. We calculated actual hurricane exposure vulnerability site scores (EVVS) through the combination of a wind pressure model, an exposure model that can incorporate simple wind dynamics within a 3-dimensional landscape and the integration of historical hurricanes data. The EVSS was calculated as a weighted function of sites exposure, hurricane frequency and maximum wind velocity. Eleven hurricanes were found to have affected CNP between 1995 and 2010. The highest EVSS’s were predicted to be on South and South-East facing sites of the park. Ground validation demonstrated that the South-solution (i.e. the South wind inflow direction) explained most of the observed tree damage (90% of the observed tree damage in the field). Incorporating historical data to the model to calculate actual hurricane exposure values, instead of potential exposure values, increased the model fit by 50%.

Nutrient- and sediment-induced macroinvertebrate drift in Honduran cloud forest streams

AbstractnMontane cloud forests are hydrologically unique, critically endangered ecosystems and frequently major sources of potable water, which have come under increasing pressure from human activities. It is therefore of vital importance that our understanding of the effects of anthropogenic stressors on the aquatic biota in these ecosystems is improved. To this end, a series of flow channel-based field experiments was performed to quantify the effects of nutrient enrichment and deposited fine sediment (two stressors commonly observed in tropical regions) on river macroinvertebrate assemblages in a cloud forest park in Honduras. Macroinvertebrate communities responded to the addition of nutrients (released from struvite) through an increased percentage abundance drifting and to elevated sediment levels with an increased percentage abundance and richness drifting in the first 24xa0h following treatment. A shift in community structure was also observed in response to elevated nutrients with lower abundances of some taxa and an overall decrease in richness. Our results indicate that increased nutrient loading and sedimentation can alter benthic macroinvertebrate community composition in high-altitude neotropical streams. Macroinvertebrate communities may be impacted via direct toxicity of nutrients and clogging of interstitial spaces and/or reductions in refugia due to sedimentation.

Host niche may determine disease-driven extinction risk

The fungal pathogen Batrachochytrium dendrobatidis (Bd) drives declines and extinctions in amphibian communities. However, not all regions and species are equally affected. Here, we show that association with amphibian aquatic habitat types (bromeliad phytotelmata versus stream) across Central America results in the odds of being threatened by Bd being five times higher in stream microhabitats. This differential threat of Bd was supported in our study by a significantly lower prevalence of Bd in bromeliad-associated amphibian species compared to riparian species in Honduran cloud forests. Evidence that the bromeliad environment is less favorable for Bd transmission is exemplified by significantly less suitable physicochemical conditions and higher abundance of Bd-ingesting micro-eukaryotes present in bromeliad water. These factors may inhibit aquatic Bd zoospore survival and the development of an environmental reservoir of the pathogen. Bromeliad phytotelmata thus may act as environmental refuges from Bd, which contribute to protecting associated amphibian communities against chytridiomycosis-driven amphibian declines that threaten the nearby riparian communities.

A new biogeographically disjunct giant gecko ( Gehyra : Gekkonidae: Reptilia) from the East Melanesian Islands

The East Melanesian Islands have been a focal area for research into island biogeography and community ecology. However, previously undescribed and biogeographically significant new species endemic to this region continue to be discovered. Here we describe a phylogenetically distinct (~20% divergence at the mitochondrial ND2 gene) and biogeographically disjunct new species of gecko in the genus Gehyra, from the Admiralty and St Matthias Islands. Gehyra rohan sp. nov. can be distinguished from all congeners by the combination of its very large size, ring of bright orange scales around the eye, moderate degree of lateral folding on the limbs and body, and aspects of head, body and tail scalation. Molecular data indicate mid to late Miocene divergence of the new species from nearest relatives occurring nearly 2000 kilometres away in Vanuatu and Fiji. Large Gehyra have not been recorded on the intervening large islands of the Bismark Archipelago (New Britain and New Ireland) and the Solomon Islands, suggesting this dispersal pre-dated the current configuration of these islands, extinction in intervening regions, or potentially elements of both. Conversely, low genetic divergence between disjunct samples on Manus and Mussau implies recent overseas dispersal via either natural or anthropogenic means.

Microdrile Oligochaeta in bromeliad pools of a Honduran cloud forest

Phytotelmata, or plant-held water bodies, often house complex aquatic invertebrate communities. Microdrile oligochaetes (Clitellata, Annelida) are known to be part of that community, but specimens are rarely identified to species level. Here we report three species of Enchytraeidae and three species of Naididae from a collection sampled in phytotelms of bromeliads in Cusuco National Park, Honduras. Two species of enchytraeids are new to science. Bryodrilus hondurensis sp. nov. is distinguished from other members of the genus by the high number of ventral chaetae, up to 11 per bundle. The genus is Holarctic and this is the southernmost record so far of a Bryodrilus species. Hemienchytraeus phytotelmatus sp. nov. is distinguished by a combination of characters, among which the huge spermathecae and seminal vesicles are most conspicuous. The genus is common in tropical and subtropical soils around the world. A third species of enchytraeids in the collection, Cernosvitoviella atrata (Bretscher), is redescribed, together with three known species of Naididae, Pristina jenkinae (Stephenson), Pristina osborni (Walton) and Pristina terrena Collado & Schmelz. Presence of ingested debris and humus in the intestine of most specimens suggests that the collected animals live and reproduce in the phytotelms. We provide a list of oligochaete species recorded so far from bromeliad pools in Central and South America.

A new genus of Psychodinae (Diptera, Psychodidae) from phytotelmata in a Honduran cloud forest

Larvae of a new species of Psychodinae, Moruseodina cusucoensis gen. et sp. nov., were collected during a biodiversity survey of aquatic invertebrates in plant held water bodies (phytotelmata) in Cusuco National Park, Honduras. The fourth instar larva, pupa and adult male are described based on reared material. The new species was difficult to place in an existing genus, thus a new genus name is proposed. Based on similarities in morphological characteristics, ecology and distribution, the species Moruseodina superba comb. nov. and Moruseodina conspicua comb. nov. are transferred from Telmatoscopus Eaton, 1904 to the new genus.xa0