Oceanographic significance of Pacific late miocene calcareous nannoplankton

An analysis of the variability in the composition and distribution of Pacific Late Miocene calcareous nannoplankton about their average biogeography shows that there are primarily two environmental factors causing that variability, climate and dissolution. Climate produces a latitudinal, biogeographic differentiation of the Late Miocene nannoflora, while selective dissolution superimposes a bathymetric differentiation of the nannoflora on that due to climate. Together, these two factors produce three distinct Late Miocene nannofloral assemblages, a high-latitude, temperate assemblage characterized by Reticulofenestra pseudoumbilica and Coccolithus pelagicus, and two tropical assemblages, their differences in composition depending on water depth and surface-water productivity: (1) in shallower water and beneath areas of higher organic production and sedimentation of calcite there is an undissolved assemblage characterized by sphenoliths, small elliptical placoliths and Coccolithus pataecus; (2) in deeper water and areas of lower productivity there is a dissolved assemblage dominated by discoasters.Selective dissolution produces most of the apparent biogeographic variation in Pacific Late Miocene nannoplankton compositions, the variation in compositions observed between the seventeen sites studied. Dissolution preferentially removes the more soluble constituents of the tropical nannoflora so that increasing dissolution tends to give tropical nannoflora a cooler, more temperate aspect. At the same time, selective dissolution shifts the composition of the warmer, tropical component towards its more resistant taxa.Nannoplankton records show a period of greatly decreased calcite dissolution in deep tropical and temperate South Pacific sites between about 8 and 10 m.y. ago. This decrease is strongly correlated with a temporary increase in the ¹³C composition of Pacific deep waters. Calcite dissolution increased during this same period in the deep North Pacific.Nannoplankton records of Late Miocene climate in the tropics are distinctly different from those at higher, south temperate latitudes. Tropical records show a sharp warming in the earliest Late Miocene after a generally cool late Middle Miocene. This was followed by a temporary cooling, nearly to Middle Miocene levels, about 7 m.y. ago. Toward the end of the Late Miocene, the tropical Pacific warmed again and remained warm into the Pliocene. Warming of temperate climates occurred much later. Not until latest Miocene did the southern the Pliocene. Warming of temperate climates occurred much later. Not until latest Miocene did the southern temperate latitudes warm appreciably. Southern subpolar climate cooled continuously through the Late Miocene. We attribute the resulting increases in the latitudinal climatic contrast across the southern Pacific Ocean to the development and migration of a strong subtropical convergence.On the basis of the nannoplankton oceanographic records we postulate that beginning about 10.5 m.y. ago Pacific surface circulation became primarily zonal and the production of deep and bottom waters in the Southern Ocean increased sharply. This produced a northward decrease in calcite preservation, an increase in benthic ¹³C, and a strong climatic gradient across southern latitudes. The period of most vigorous deep Pacific circulation ended 7 m.y. ago in response, we speculate, to the reduced ocean salinities during the Messinian.     

Climate change creates rapid species turnover in montane communities

Recent decades have seen substantial changes in patterns of biodiversity worldwide. Simultaneously, climate change is producing a widespread pattern of species’ range shifts to higher latitudes and higher elevations, potentially creating novel assemblages as species shift at different rates. However, the direct link between species’ turnover as a result of climate‐induced range shifts has not yet been empirically evaluated. We measured rates of species turnover associated with species’ range shifts in relatively undisturbed montane areas in Asia, Europe, North America, South America, and the Indo‐Pacific. We show that species turnover is rapidly creating novel assemblages, and this can be explained by variable changes in species’ range limits following warming. Across all the areas we analyzed, mean species’ turnover was 12% per decade, which was nearly balanced between the loss of existing co‐occurrences and the gain of novel co‐occurrences. Turnover appears to be more rapid among ectothermic assemblages, and some evidence suggests tropical assemblages may be responding at more rapid rates than temperate assemblages.     

Climate‐driven substitution of habitat‐forming species leads to reduced biodiversity within a temperate marine community

Aim

In marine ecosystems, habitat‐forming species (HFS) such as reef‐building corals and canopy‐forming macroalgae alter local environmental conditions and can promote biodiversity by providing biogenic living space for a vast array of associated organisms. We examined community‐level impacts of observed climate‐driven shifts in the relative abundances of two superficially similar HFS, the warm‐water kelp Laminaria ochroleuca and the cool‐water kelp Laminaria hyperborea.

Location

Western English Channel, north‐east Atlantic

Methods

We compared algal and invertebrate assemblages associated with kelp stipes and holdfasts, across multiple sites and sampling events. Significant differences were recorded in the structure of assemblages between the host kelp species at each site and event.

Results

Assemblages associated with stipes of the cool‐water HFS were, on average, >12 times more diverse and supported >3600 times more biomass compared with the warm‐water HFS. Holdfast assemblages also differed significantly between species, although to a lesser extent than those associated with stipes. Overall, assemblages associated with the warm‐water HFS were markedly impoverished and comprised far fewer rare or unique taxa.

Main conclusions

While previous research has shown how climate‐driven loss of HFS can cause biodiversity loss, our study demonstrates that climate‐driven substitutions of HFS can also lead to impoverished assemblages. The indirect effects of climate change remain poorly resolved, but shifts in the distributions and abundances of HFS may invoke widespread ecological change, especially in marine ecosystems where facilitative interactions are particularly strong.     

Annual recurrence of prokaryotic climax communities in shallow waters of the North Mediterranean

In temperate coastal environments, wide fluctuations of biotic and abiotic factors drive microbiome dynamics. To link recurrent ecological patterns with planktonic microbial communities, we analysed a monthly-sampled 3-year time series of 16S rRNA amplicon sequencing data, alongside environmental variables, collected at two stations in the northern Adriatic Sea. Time series multivariate analyses allowed us to identify three stable, mature communities (climaxes), whose recurrence was mainly driven by changes in photoperiod and temperature. Mixotrophs (e.g., Ca. Nitrosopumilus, SUP05 clade, and Marine Group II) thrived under oligotrophic, low-light conditions, whereas copiotrophs (e.g., NS4 and NS5 clades) bloomed at higher temperatures and substrate availability. The early spring climax was characterised by a more diverse set of amplicon sequence variants, including copiotrophs associated with phytoplankton-derived organic matter degradation, and photo-auto/heterotrophic organisms (e.g., Synechococcus sp., Roseobacter clade), whose rhythmicity was linked to photoperiod lengthening. Through the identification of recurrent climax assemblages, we begin to delineate a typology of ecosystem based on microbiome composition and functionality, allowing for the intercomparison of microbial assemblages among different biomes, a still underachieved goal in the omics era.     

Temperate macroalgae impacts tropical fish recruitment at forefronts of range expansion

Warming waters and changing ocean currents are increasing the supply of tropical fish larvae to temperature regions where they are exposed to novel habitats, namely temperate macroalgae and barren reefs. Here, we use underwater surveys on the temperate reefs of south-eastern (SE) Australia and western Japan (~33.5°N and S, respectively) to investigate how temperate macroalgal and non-macroalgal habitats influence recruitment success of a range of tropical fishes. We show that temperate macroalgae strongly affected recruitment of many tropical fish species in both regions and across three recruitment seasons in SE Australia. Densities and richness of recruiting tropical fishes, primarily planktivores and herbivores, were over seven times greater in non-macroalgal than macroalgal reef habitat. Species and trophic diversity (K-dominance) were also greater in non-macroalgal habitat. Temperate macroalgal cover was a stronger predictor of tropical fish assemblages than temperate fish assemblages, reef rugosities or wave exposure. Tropical fish richness, diversity and density were greater on barren reef than on reef dominated by turfing algae. One common species, the neon damselfish (Pomacentrus coelestis), chose non-macroalgal habitat over temperate macroalgae for settlement in an aquarium experiment. This study highlights that temperate macroalgae may partly account for spatial variation in recruitment success of many tropical fishes into higher latitudes. Hence, habitat composition of temperate reefs may need to be considered to accurately predict the geographic responses of many tropical fishes to climate change.

     

Opposed latitudinal patterns of network‐derived and dietary specialization in avian plant–frugivore interaction systems

Latitudinal patterns of biodiversity have been studied for centuries, but it is only during the last decades that species interaction networks have been used to examine the proposed latitudinal gradient of biotic specialization. These studies have given idiosyncratic results, which may either be because of genuine biological differences between systems, different concepts and scales used to quantify biotic specialization or because the methodological approaches used to compare interaction networks were inappropriate. Here we carefully examine the latitudinal specialization gradient using a global dataset of avian plant–frugivore assemblages and interaction networks. In particular, we test whether network‐derived specialization patterns differ from patterns based on assemblage‐level information on avian dietary preferences on specific food types. We found that network‐derived measures of specialization (complementary specialization H₂′ and < d’>, modularity Q) increased with latitude, i.e. frugivorous birds divide the niche of fruiting plants most finely at high latitudes where they also formed more modular interaction networks than at tropical latitudes. However, the strength and significance of the relationship between specialization metrics and latitude was influenced by the methodological approach. On the other hand, assemblage‐level information on avian specialization on fruit diet (i.e. the proportion of obligate frugivorous bird species feeding primarily on fruit) revealed an opposed latitudinal pattern as more bird species were specialized on fruit diet in tropical than in temperate assemblages. This difference in the latitudinal specialization gradient reflects that obligate frugivores require a high diversity of fruit plants, as observed in tropical systems, and fulfil more generalized roles in plant–frugivore networks than bird species feeding on different food types. Future research should focus on revealing the underlying ecological, historical and evolutionary mechanisms shaping these patterns. Our results highlight the necessity of comparing different scales of biotic specialization for a better understanding of geographical patterns of specialization in resource–consumer interactions.     

‘Stick with your own kind,or hang with the locals?’ Implications of shoaling strategy for tropical reef fish on a range‐expansion frontline

Range shifts of tropical marine species to temperate latitudes are predicted to increase as a consequence of climate change. To date, the research focus on climate‐mediated range shifts has been predominately dealt with the physiological capacity of tropical species to cope with the thermal challenges imposed by temperate latitudes. Behavioural traits of individuals in the novel temperate environment have not previously been investigated, however, they are also likely to play a key role in determining the establishment success of individual species at the range‐expansion forefront. The aim of this study was to investigate the effect of shoaling strategy on the performance of juvenile tropical reef fishes that recruit annually to temperate waters off the south east coast of Australia. Specifically, we compared body‐size distributions and the seasonal decline in abundance through time of juvenile tropical fishes that shoaled with native temperate species (‘mixed’ shoals) to those that shoaled only with conspecifics (as would be the case in their tropical range). We found that shoaling with temperate native species benefitted juvenile tropical reef fishes, with individuals in ‘mixed’ shoals attaining larger body‐sizes over the season than those in ‘tropical‐only’ shoals. This benefit in terms of population body‐size distributions was accompanied by greater social cohesion of ‘mixed’ shoals across the season. Our results highlight the impact that sociality and behavioural plasticity are likely to play in determining the impact on native fish communities of climate‐induced range expansion of coral reef fishes.     

Diversification in tropics and subtropics following the mid‐Miocene climate change: A case study of the spider genus Nesticella

Caves may offer suitable refugia for troglophilic invertebrates during periods of unfavourable climatic conditions because of their stable microclimates. As a consequence, allopatric divergence from their epigean counterparts may occur, leading to formation of truly hypogean communities (the Climatic Relict Hypothesis). Unlike the well‐studied effects of Pleistocene glaciations, we know little about how ancient climate changes drove the development of cave‐dwelling organisms living at both middle and lower latitudes. We investigate the evolutionary history of the troglophilic spider genus Nesticella (Araneae, Nesticidae) in relation to Asian Neogene (23–2.6 Ma) climatic changes. Our analyses discern clear differences in the evolution of the two main clades of Nesticella, which occur in temperate/subtropical and tropical latitudes. Eastern Asian Nesticella gradually evolved greater sedentariness and a strict subterranean lifestyle starting from the middle Miocene Epoch (~15–14 Ma) in conjunction with the progressive deterioration of the climate and vegetational shifts. Caves appear to have acted as refugia because of their internally uniform temperature and humidity, which allowed these spiders to survive increasing external seasonality and habitat loss. In contrast, a uniform accumulation of lineages, long‐lasting times for dispersals and the lack of a comparable habitat shifting characterized the tropical lineage. This difference in pattern likely owes to the mild effects of climate change at low latitudes and the consequent lack of strong climatic drivers in tropical environments. Thus, the mid‐Miocene climatic shift appears to be the major evolutionary force shaping the ecological differences between Asian troglophilic invertebrates and the driver of the permanent hypogean communities in middle latitudes.     

Effects of forest degradation on microbial communities and soil carbon cycling: A global meta‐analysis

Aim

The aim was to explore how conversions of primary or secondary forests to plantations or agricultural systems influence soil microbial communities and soil carbon (C) cycling.

Location

Global.

Time period

1993–2017.

Major taxa studied

Soil microbes.

Methods

A meta‐analysis was conducted to examine effects of forest degradation on soil properties and microbial attributes related to microbial biomass, activity, community composition and diversity based on 408 cases from 119 studies in the world.

Results

Forest degradation decreased the ratios of K‐strategists to r‐strategists (i.e., ratios of fungi to bacteria, Acidobacteria to Proteobacteria, Actinobacteria to Bacteroidetes and Acidobacteria + Actinobacteria to Proteobacteria + Bacteroidetes). The response ratios (RRs) of the K‐strategist to r‐strategist ratios to forest degradation decreased and increased with increased RRs of soil pH and soil C to nitrogen ratio (C:N), respectively. Forest degradation increased the bacterial alpha‐diversity indexes, of which the RRs increased and decreased as the RRs of soil pH and soil C:N increased, respectively. The overall RRs across all the forest degradation types ranked as microbial C (?40.4%) > soil C (?33.3%) > microbial respiration (?18.9%) > microbial C to soil C ratio (qMBC; ?15.9%), leading to the RRs of microbial respiration rate per unit microbial C (qCO₂) and soil C decomposition rate (respiration rate per unit soil C), on average, increasing by +43.2 and +25.0%, respectively. Variances of the RRs of qMBC and qCO₂ were significantly explained by the soil C, soil C:N and mean annual precipitation.

Main conclusions

Forest degradation consistently shifted soil microbial community compositions from K‐strategist dominated to r‐strategist dominated, altered soil properties and stimulated microbial activity and soil C decomposition. These results are important for modelling the soil C cycling under projected global land‐use changes and provide supportive evidence for applying the macroecology theory on ecosystem succession and disturbance in soil microbial ecology.     

The biogeographical distribution of microfungi associated with three palm species from tropical and temperate habitats

The microfungi of three palm species were investigated in their natural habitats and in habitats where the palms were cultivated outside their natural ranges. The palms that were selected differed in their habitats and ecology. Archontophoenix alexandrae is endemic to tropical rainforests in Australia, Cocos nucifera is pan‐tropical and Trachycarpus fortunei occurs in warm‐temperate China. Different assemblages of fungi were found in association with palms in temperate regions as compared to those in tropical regions. These differences were more related to climatic influences than to the hosts sampled, as few fungi were host‐species specific. The status of the hosts at the site, i.e. indigenous or introduced, and the degree of disturbance of the habitats within which the palms grew were also influential. When sampled in its natural habitat, Archontophoenix alexandrae had a distinct palmicolous mycota typical of other palms in tropical rainforests. Outside of the palm’s natural habitat, a widely different mycota were recorded that comprised tropical species of a more plurivorous nature. A similar plurivorous assemblage characterized the fungi associated with Cocos nucifera, probably due to the palm’s long history of cultivation. Similarly, plurivorous, but temperate or widespread fungi were associated with Trachycarpus fortunei, both within and outside of its natural habitat. This palm is also highly cultivated. A reduction in palm fungi associated with palms in disturbed habitats has implications for conservation of these fungi. However, it is acknowledged that the data for fungal diversity and distribution is incomplete and fragmentary.     

Leaf Quality of Some Tropical and Temperate Tree Species as Food Resource for Stream Shredders

We tested the hypotheses that (1) plant defenses against consumers increase in the tropics, and that these differences in quality are perceived by detritivores; and (2) microbial conditioning of leaf litter is important for the feeding ecology of shredders from both geographical regions. We compared quality parameters of 8 tree species from Portugal and 8 from Venezuela. The tropical leaves were tougher, but did not differ from temperate leaves in terms of N, C: N, and polyphenols. In multiple‐choice experiments, shredders from Portugal (Sericostoma vittatum and Chaetopteryx lusitanica) and from Venezuela (Nectopsyche argentata and Phylloicus priapulus) discriminated among conditioned leaves, preferentially consuming softer leaves. In another set of experiments, all shredders preferentially fed on conditioned rather than unconditioned leaves, grew faster when fed conditioned than unconditioned leaves and fed more on temperate than tropical leaves. We conclude that leaf litter from the tropics is a low‐quality resource compared to leaves in temperate systems, because of differences in toughness, and that tropical shredders benefit from microbial colonization, as previously demonstrated for temperate systems. We suggest that leaf toughness could be one explanation for the reported paucity of shredders in some tropical streams. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Plankton dynamics under different climate conditions in tropical freshwater systems (a reply to the comment by Sarmento,Amado & Descy, )

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Phytoplankton distribution along trophic gradients within and among reservoirs in Catalonia (Spain)

1. Longitudinal gradients in the epilimnetic waters of stratified reservoirs provide a useful database to study changing environmental conditions. The spatial distribution, assemblage structure and specific adaptations of phytoplankton assemblages can be analysed along these gradients over short time scales. 2. Four reservoirs with a similar typology, located along an altitudinal gradient in the same eco‐region, were sampled along their longitudinal axes. In total, 19 sampling stations provided a trophic spectrum, ranging from oligo‐mesotrophy to hypertrophy, which was quantified by calculating the trophic state index of each sampling station in the four reservoirs. 3. Several patterns in phytoplankton assemblage structure were detected. Total chlorophyll‐a (Chl‐a), biovolume, abundance and the relative biomass contribution of the main algal groups (chlorophytes, cyanobacteria, cryptophytes and diatoms) were highly correlated with their location along the trophic gradient. 4. We also adopted the functional classification of Reynolds et al. (2002) : this effectively summarized differences among phytoplankton assemblages under varying resource‐limiting combinations, especially nutrients and underwater light climate. 5. In terms of relationships with the trophic gradient, diatoms and cyanobacteria exhibited significant opposing trends in both their relative chlorophyll contribution to total Chl‐a and biovolume. Chlorophytes were more abundant at an intermediate position along the trophic spectrum. 6. The identified patterns are consistent with models of self‐organization of phytoplankton assemblages. In particular, light availability was a strong determinant of size and shape diversity, especially in hypertrophic conditions, where ‘R‐strategist’, needle shaped species, dominated the system. In contrast, under decreased availability of nutrients and higher light extinction coefficients (K_d), the system was co‐dominated by C‐ and S‐strategist species, having shapes with a higher surface/volume ratio.     

Diversity and assemblage structure of phytophagous Hemiptera along a latitudinal gradient: predicting the potential impacts of climate change

Aims The aims were (1) to assess the species richness and structure of phytophagous Hemiptera communities along a latitudinal gradient, (2) to identify the importance of rare species in structuring these patterns, and (3) to hypothesize about how phytophagous Hemiptera communities may respond to future climate change. Location East coast of Australia. Methods Four latitudes within the 1150 km coastal distribution of Acacia falcata were selected. The insect assemblage on the host plant Acacia falcata was sampled seasonally over two years. Congeneric plant species were also sampled at the sites. Results Ninety‐eight species of phytophagous Hemiptera were collected from A. falcata. Total species richness was significantly lower at the most temperate latitude compared to the three more tropical latitudes. We classified species into four climate change response groups depending on their latitudinal range and apparent host specificity. Pairwise comparisons between groups showed that the cosmopolitan, generalist feeders and specialists had a similar community structure to each other, but the climate generalists had a significantly different structure. Fifty‐seven species were identified as rare. Most of these rare species were phloem hoppers and their removal from the dataset led to changes in the proportional representation of all guilds in two groups: the specialist and generalist feeders. Main conclusions We found no directional increase in phytophagous Hemiptera species richness. This indicates that, at least in the short term, species richness patterns of these communities may be similar to that found today. As the climate continues to change, however, we might expect some increases in species richness at the more temperate latitudes as species migrate in response to shifting climate zones. In the longer term, more substantial changes in community composition will be expected because the rare species, which comprise a large fraction of these communities, will be vulnerable to both direct climatic changes, and indirect effects via changes to their host's distribution.     

Refugia under threat: Mass bleaching of coral assemblages in high‐latitude eastern Australia

Environmental anomalies that trigger adverse physiological responses and mortality are occurring with increasing frequency due to climate change. At species' range peripheries, environmental anomalies are particularly concerning because species often exist at their environmental tolerance limits and may not be able to migrate to escape unfavourable conditions. Here, we investigated the bleaching response and mortality of 14 coral genera across high‐latitude eastern Australia during a global heat stress event in 2016. We evaluated whether the severity of assemblage‐scale and genus‐level bleaching responses was associated with cumulative heat stress and/or local environmental history, including long‐term mean temperatures during the hottest month of each year (SST_LTMAX), and annual fluctuations in water temperature (SST_VAR) and solar irradiance (PARZ_VAR). The most severely‐bleached genera included species that were either endemic to the region (Pocillopora aliciae) or rare in the tropics (e.g. Porites heronensis). Pocillopora spp., in particular, showed high rates of immediate mortality. Bleaching severity of Pocillopora was high where SST_LTMAX was low or PARZ_VAR was high, whereas bleaching severity of Porites was directly associated with cumulative heat stress. While many tropical Acropora species are extremely vulnerable to bleaching, the Acropora species common at high latitudes, such as A. glauca and A. solitaryensis, showed little incidence of bleaching and immediate mortality. Two other regionally‐abundant genera, Goniastrea and Turbinaria, were also largely unaffected by the thermal anomaly. The severity of assemblage‐scale bleaching responses was poorly explained by the environmental parameters we examined. Instead, the severity of assemblage‐scale bleaching was associated with local differences in species abundance and taxon‐specific bleaching responses. The marked taxonomic disparity in bleaching severity, coupled with high mortality of high‐latitude endemics, point to climate‐driven simplification of assemblage structures and progressive homogenisation of reef functions at these high‐latitude locations.     

Abrupt changes in Great Britain vegetation carbon projected under climate change

Past abrupt ‘regime shifts’ have been observed in a range of ecosystems due to various forcing factors. Large‐scale abrupt shifts are projected for some terrestrial ecosystems under climate change, particularly in tropical and high‐latitude regions. However, there is very little high‐resolution modelling of smaller‐scale future projected abrupt shifts in ecosystems, and relatively less focus on the potential for abrupt shifts in temperate terrestrial ecosystems. Here, we show that numerous climate‐driven abrupt shifts in vegetation carbon are projected in a high‐resolution model of Great Britain's land surface driven by two different climate change scenarios. In each scenario, the effects of climate and CO₂ combined are isolated from the effects of climate change alone. We use a new algorithm to detect and classify abrupt shifts in model time series, assessing the sign and strength of the non‐linear responses. The abrupt ecosystem changes projected are non‐linear responses to climate change, not simply driven by abrupt shifts in climate. Depending on the scenario, 374–1,144 grid cells of 1.5 km × 1.5 km each, comprising 0.5%–1.5% of Great Britain's land area show abrupt shifts in vegetation carbon. We find that abrupt ecosystem shifts associated with increases (rather than decreases) in vegetation carbon, show the greatest potential for early warning signals (rising autocorrelation and variance beforehand). In one scenario, 89% of abrupt increases in vegetation carbon show increasing autocorrelation and variance beforehand. Across the scenarios, 81% of abrupt increases in vegetation carbon have increasing autocorrelation and 74% increasing variance beforehand, whereas for decreases in vegetation carbon these figures are 56% and 47% respectively. Our results should not be taken as specific spatial or temporal predictions of abrupt ecosystem change. However, they serve to illustrate that numerous abrupt shifts in temperate terrestrial ecosystems could occur in a changing climate, with some early warning signals detectable beforehand.     

Pelagic phytoplankton community change‐points across nutrient gradients and in response to invasive mussels

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Does morphology predict behavior? Correspondence between behavioral and morphometric data in a Tyrant‐flycatcher (Tyrannidae) assemblage in the Santa Marta Mountains,Colombia

ABSTRACT Morphology is commonly used as a predictor of ecological relationships among species when studying local assemblages of Neotropical birds. Nevertheless, most evidence supporting ecomorphological correspondence in birds comes from studies of communities and not from local assemblages and, moreover, from temperate latitudes. To increase our understanding of ecomorphological correspondence in Neotropical assemblages, we used three multivariate approaches to evaluate correspondence between morphological and foraging behavior data in a tyrant‐flycatcher assemblage (N= 12 species) in the Santa Marta Mountains in Colombia. Principal components analyses revealed similar species ordinations when using morphological measurements (beak size and shape, tarsus length, wing length, and tail length) or behavioral data (behavioral types of searching for prey and prey capture) separately. Discriminant function analyses tested the ability of morphological traits to predict foraging behavior, showing that more than 90% of all measured individuals (N= 267) were correctly classified in previously defined categories of search and attack behavior. Finally, Canonical correlation analyses revealed a significant correlation between morphological data and two independent datasets of search and attack behavior. Our results demonstrate that morphology can accurately predict ecology in an assemblage of Neotropical tyrannids, and similar results have been reported in previous studies of temperate Tyrant‐flycatchers. Our results also show that bill size and shape, wing length, and tarsus length are the best predictors of foraging behavior in this assemblage. Testing for ecomorphological correspondence in other Neotropical taxa would help identify subsets of phenotypic traits that could be used for a practical, but reliable, determination of ecological relationships within different assemblages.     

Environmental controls on the distribution and diversity of lentic Chironomidae (Insecta: Diptera) across an altitudinal gradient in tropical South America

To predict the response of aquatic ecosystems to future global climate change, data on the ecology and distribution of keystone groups in freshwater ecosystems are needed. In contrast to mid‐ and high‐latitude zones, such data are scarce across tropical South America (Neotropics). We present the distribution and diversity of chironomid species using surface sediments of 59 lakes from the Andes to the Amazon (0.1–17°S and 64–78°W) within the Neotropics. We assess the spatial variation in community assemblages and identify the key variables influencing the distributional patterns. The relationships between environmental variables (pH, conductivity, depth, and sediment organic content), climatic data, and chironomid assemblages were assessed using multivariate statistics (detrended correspondence analysis and canonical correspondence analysis). Climatic parameters (temperature and precipitation) were most significant in describing the variance in chironomid assemblages. Temperature and precipitation are both predicted to change under future climate change scenarios in the tropical Andes. Our findings suggest taxa of Orthocladiinae, which show a preference to cold high‐elevation oligotrophic lakes, will likely see range contraction under future anthropogenic‐induced climate change. Taxa abundant in areas of high precipitation, such as Micropsectra and Phaenopsectra, will likely become restricted to the inner tropical Andes, as the outer tropical Andes become drier. The sensitivity of chironomids to climate parameters makes them important bio‐indicators of regional climate change in the Neotropics. Furthermore, the distribution of chironomid taxa presented here is a vital first step toward providing urgently needed autecological data for interpreting fossil chironomid records of past ecological and climate change from the tropical Andes.     

Contrasting responses to water deficits of Nothofagus species from tropical New Guinea and high‐latitude temperate forests: can rainfall regimes constrain latitudinal range?

Aim Comparative responses of Nothofagus species to water deficits were studied to determine whether rainfall regimes could limit the latitudinal ranges of tropical and temperate forest species. Location The study species are native to New Guinea, New Caledonia, Australia, New Zealand, Chile and Argentina. Methods Seedlings of Nothofagus species from a broad latitudinal range were grown in a common environment. Changes in conductance, relative water content and water potential were measured in detached shoots, and together with measurements of tissue injury and biomass allocation, were compared between tropical and temperate species. Results Differences in responses to water deficits between tropical and temperate species appear to reflect differences in climate regimes. In particular, species native to ever‐wet rainfall regimes in New Guinea, where water deficits are generally likely to be short‐lived, were effective at conserving water by reduced stomatal conductance. In contrast, high‐latitude evergreen species on average showed greater development of traits that should enhance water uptake. This was particularly evident in Nothofagus cunninghamii from southern Australia, which developed low water potentials at moderate levels of tissue water deficit and higher root:leaf biomass than tropical species, potentially allowing carbon assimilation to be maximized during warmer, but drier, summer months. However, water relations varied among high‐latitude species. In particular, deciduous species on average showed higher rates of conductance, even during moderate levels of tissue water deficit, than evergreen species. Main conclusions The tropical species appear to conserve water during periods of water deficit (relative to temperate species), which is unlikely to have substantial opportunity costs for growth in ever‐wet climates. However, spread of tropical species to higher latitudes may be limited by water conservation strategies that limit carbon gain in climates in which temperature seasonality is often paired with drier summers. Evergreen species from high latitudes, such as N. cunninghamii, commonly showed traits that should increase water uptake. However, this strategy, while probably maximizing growth in temperate climates with cool winters and drier summers, must limit competitiveness at lower latitudes in summer‐wet climates. We conclude that responses to water regimes may make a significant contribution to the latitudinal limits of some evergreen rain forest species.