Divergent drivers of leaf trait variation within species, among species, and among functional groups.

Understanding variation in leaf functional traits-including rates of photosynthesis and respiration and concentrations of nitrogen and phosphorus-is a fundamental challenge in plant ecophysiology. When expressed per unit leaf area, these traits typically increase with leaf mass per area (LMA) within species but are roughly independent of LMA across the global flora. LMA is determined by mass components with different biological functions, including photosynthetic mass that largely determines metabolic rates and contains most nitrogen and phosphorus, and structural mass that affects toughness and leaf lifespan (LL). A possible explanation for the contrasting trait relationships is that most LMA variation within species is associated with variation in photosynthetic mass, whereas most LMA variation across the global flora is associated with variation in structural mass. This hypothesis leads to the predictions that (i) gas exchange rates and nutrient concentrations per unit leaf area should increase strongly with LMA across species assemblages with low LL variance but should increase weakly with LMA across species assemblages with high LL variance and that (ii) controlling for LL variation should increase the strength of the above LMA relationships. We present analyses of intra- and interspecific trait variation from three tropical forest sites and interspecific analyses within functional groups in a global dataset that are consistent with the above predictions. Our analysis suggests that the qualitatively different trait relationships exhibited by different leaf assemblages can be understood by considering the degree to which photosynthetic and structural mass components contribute to LMA variation in a given assemblage

Divergent drivers of leaf trait variation within species, among species, and among functional groups

Understanding variation in leaf functional traits—including rates of photosynthesis and respiration and concentrations of nitrogen and phosphorus—is a fundamental challenge in plant ecophysiology. When expressed per unit leaf area, these traits typically increase with leaf mass per area (LMA) within species but are roughly independent of LMA across the global flora. LMA is determined by mass components with different biological functions, including photosynthetic mass that largely determines metabolic rates and contains most nitrogen and phosphorus, and structural mass that affects toughness and leaf lifespan (LL). A possible explanation for the contrasting trait relationships is that most LMA variation within species is associated with variation in photosynthetic mass, whereas most LMA variation across the global flora is associated with variation in structural mass. This hypothesis leads to the predictions that (i) gas exchange rates and nutrient concentrations per unit leaf area should increase strongly with LMA across species assemblages with low LL variance but should increase weakly with LMA across species assemblages with high LL variance and that (ii) controlling for LL variation should increase the strength of the above LMA relationships. We present analyses of intra- and interspecific trait variation from three tropical forest sites and interspecific analyses within functional groups in a global dataset that are consistent with the above predictions. Our analysis suggests that the qualitatively different trait relationships exhibited by different leaf assemblages can be understood by considering the degree to which photosynthetic and structural mass components contribute to LMA variation in a given assemblage

Climate sensitive size-dependent survival in tropical trees

Survival rates of large trees determine forest biomass dynamics. Survival rates of small trees have been linked to mechanisms that maintain biodiversity across tropical forests. How species survival rates change with size offers insight into the links between biodiversity and ecosystem function across tropical forests. We tested patterns of size-dependent tree survival across the tropics using data from 1,781 species and over 2 million individuals to assess whether tropical forests can be characterized by size-dependent life-history survival strategies. We found that species were classifiable into four ‘survival modes’ that explain life-history variation that shapes carbon cycling and the relative abundance within forests. Frequently collected functional traits, such as wood density, leaf mass per area and seed mass, were not generally predictive of the survival modes of species. Mean annual temperature and cumulative water deficit predicted the proportion of biomass of survival modes, indicating important links between evolutionary strategies, climate and carbon cycling. The application of survival modes in demographic simulations predicted biomass change across forest sites. Our results reveal globally identifiable size-dependent survival strategies that differ across diverse systems in a consistent way. The abundance of survival modes and interaction with climate ultimately determine forest structure, carbon storage in biomass and future forest trajectories

Identifying indicator species of elevation: Comparing the utility of woody plants, ants and moths for long-term monitoring

© 2016 Ecological Society of Australia. Ecologists have found the distributions of many groups of organisms to be elevationally stratified. Consequently, various taxa (or species) have been proposed as indicators for inclusion within long-term monitoring programmes to quantify the ecological impacts of future climatic change. Ideal indicators should be restricted to a particular elevational range (i.e. have high specificity) and be readily detectable across space and time (i.e. have high fidelity). This, however, has not been rigorously tested for elevational studies. We employed a spatially and temporally replicated sampling design to test the utility of tree, ant, and canopy and understorey moth species as indicators of elevation within continuous subtropical rainforest of eastern Australia. Using the classical indicator value protocol, we tested (i) whether the number of indicator species (all taxa) found in the observed data was significantly greater than the number obtained by chance; (ii) whether the indicator species (ants and moths) identified from one sampling season responded to elevation in a similar way in samples obtained from other seasons; and (iii) whether the indicator species (ants) identified from one elevational transect responded to elevation in a similar way in a nearby transect that incorporated similar elevational ranges. All groups had significantly greater numbers of indicator species than expected by chance. Temporal fidelity of moth indicator species was lower than that of ants as the suite of moth indicator species showed high seasonal variation. In contrast, ants showed high spatial and temporal fidelity. Most ant indicator species were, however, indicative of low and mid-elevations, and only one species was indicative of the highest elevation, suggesting their relatively low conservation significance in relation to climate warming in this region. It is essential that we understand how spatial and temporal variation affects the distributions of different taxonomic groups when incorporating multiple taxa for long-term monitoring programmes.Link_to_subscribed_fulltex

Occurrence of ants, beetles, cockroaches, flies and spiders on islands of the Capricorn and Bunker Group, Queensland coast

Recent progress in island biogeography indicates that classical island biogeography alone cannot encapsulate the complex and dynamic nature of island biogeographical processes. Factors such as habitat complexity and connectivity, and in the face of the Anthropocene, human disturbance and invasive species, may influence insular communities. The relative importance of these factors, however, may differ among groups of biota. Here we employed an information theoretic approach to investigate factors likely to explain patterns in species richness and assemblage composition of five different groups of arthropods (ants, beetles, flies, spiders and cockroaches) and native and exotic plants within an insular community