Behavioural flexibility predicts invasion success in birds introduced to New Zealand

A fundamental question in ecology is whether there are evolutionary characteristics of species that make some better than others at invading new communities. In birds, nesting habits, sexually selected traits, migration, clutch size and body mass have been suggested as important variables, but behavioural flexibility is another obvious trait that has received little attention. Behavioural flexibility allows animals to respond more rapidly to environmental changes and can therefore be advantageous when invading novel habitats. Behavioural flexibility is linked to relative brain size and, for foraging, has been operationalised as the number of innovations per taxon reported in the short note sections of ornithology journals. Here, we use data on avian species introduced to New Zealand and test the link between forebrain size, feeding innovation frequency and invasion success. Relative brain size was, as expected, a significant predictor of introduction success, after removing the effect of introduction effort. Species with relatively larger brains tended to be better invaders than species with smaller ones. Introduction effort, migratory strategy and mode of juvenile development were also significant in the models. Pair-wise comparisons of closely related species indicate that successful invaders also showed a higher frequency of foraging innovations in their region of origin. This study provides the first evidence in vertebrates of a general set of traits, behavioural flexibility, that can potentially favour invasion success.     

Behavioural flexibility and invasion success in birds

Behavioural flexibility has long been thought to provide advantages for animals when they invade novel environments. This hypothesis has recently received empirical support in a study of avian species introduced to New Zealand, but it remains to be determined whether behavioural flexibility is a general mechanism influencing invasion success. In this study, we examined introduction success of 69 bird species in different regions of the world as a function of their degree of behavioural flexibility. Specifically, we predicted that species with relatively large brains and a high frequency of foraging innovations in their area of origin should show a higher probability of establishing themselves where they were introduced than species with small brains and low innovation frequencies. An analysis with general linear modelling (GLM) supported the prediction for relative brain size, even when controlling for phylogenetic biases and potential confounding variables. The only covariates that remained with relative brain size were plumage dimorphism, human commensalism and nest site. A pairwise comparison of closely related species also revealed that successful invaders showed a higher frequency of foraging innovations in their region of origin. This result held even when differences in research effort between species were considered. Overall, the results confirm and generalize the hypothesis that behavioural flexibility is a major determinant of invasion success in birds.     

Nestling telomere shortening,but not telomere length,reflects developmental stress and predicts survival in wild birds

Developmental stressors often have long-term fitness consequences, but linking offspring traits to fitness prospects has remained a challenge. Telomere length predicts mortality in adult birds, and may provide a link between developmental conditions and fitness prospects. Here, we examine the effects of manipulated brood size on growth, telomere dynamics and post-fledging survival in free-living jackdaws. Nestlings in enlarged broods achieved lower mass and lost 21% more telomere repeats relative to nestlings in reduced broods, showing that developmental stress accelerates telomere shortening. Adult telomere length was positively correlated with their telomere length as nestling (r = 0.83). Thus, an advantage of long telomeres in nestlings is carried through to adulthood. Nestling telomere shortening predicted post-fledging survival and recruitment independent of manipulation and fledgling mass. This effect was strong, with a threefold difference in recruitment probability over the telomere shortening range. By contrast, absolute telomere length was neither affected by brood size manipulation nor related to survival. We conclude that telomere loss, but not absolute telomere length, links developmental conditions to subsequent survival and suggest that telomere shortening may provide a key to unravelling the physiological causes of developmental effects on fitness.     

Native species richness buffers invader impact in undisturbed but not disturbed grassland assemblages

Many systems are prone to both exotic plant invasion and frequent natural disturbances. Native species richness can buffer the effects of invasion or disturbance when imposed in isolation, but it is largely unknown whether richness provides substantial resistance against invader impact in the face of disturbance. We experimentally examined how disturbance (drought/burning) influenced the impact of three exotic invaders (Centaurea stoebe, Linaria dalmatica, or Potentilla recta) on native abundance across a gradient of species richness, using previously constructed grassland assemblages. We found that invaders had higher cover in experimentally disturbed plots than in undisturbed plots across all levels of native species richness. Although exotic species varied in cover, all three invaders had significant impacts on native cover in disturbed plots. Regardless of disturbance, however, invader cover diminished with increasing richness. Invader impacts on native cover also diminished at higher richness levels, but only in undisturbed plots. In disturbed plots, invaders strongly impacted native cover across all richness levels, as disturbance favoured invaders over native species. By examining these ecological processes concurrently, we found that disturbance exacerbated invader impacts on native abundance. Although diversity provided a buffering effect against invader impact without disturbance, the combination of invasion and disturbance markedly depressed native abundance, even in high richness assemblages.     

Prehistoric species richness of birds on oceanic islands

Using data on prehistoric and modern birds from seven islands in the Kingdom of Tonga, we demonstrate that there is no positive relationship between species richness (S) and island area (A) over the observed range of A (1.8–259 km²). The uniform S‐values occur across more than three orders of magnitude of A when prehistoric data are included, and the strongest predictor of S on any island is the level of fossil sampling (number of identified bones). Below a minimum value for A (in Tonga < 1.8 km²), S declines to zero as A does the same. Within the ranges of island elevation (E) and inter‐island isolation (I) among the seven islands, neither E (11–312 m) nor I (0.6–38 km) has much if any effect on S. Under natural (pre‐human) conditions, a positive species‐area relationship may not be a valid generalization for birds on oceanic islands.     

The relationship among area, elevation, and regional species richness in neotropical birds

The elevational gradient of species richness is often claimed to mirror the latitudinal gradient and has traditionally been explained by assuming a decrease in productivity with elevation and more recently by Rapoport's rule. The influence of area on the pattern has rarely been considered. Analyses of all South American tropical land birds (more than one-fourth of the extant bird species on Earth) are used to examine four species richness/elevation models: null model, Rapoport's rule, and monotonic or hump-shaped productivity/species richness relationships. To quantify the area effect, species-area curves were created for seven elevational zones. Not accounting for area, species richness declined monotonically with elevation, but area accounted for 67%-91% of the variation in species richness per zone. When area was factored out, a hump-shaped pattern emerged, with more species in the 500-1,000-m (P<.005) and 1,000-1,500-m zones (P<.10) than in the 0-500-m zone. Rapoport's rule and the monotonic productivity/species richness relationship were thus not supported. Instead, elevational turnover rates and numbers of shared species between zones suggested that the hump-shaped pattern reflects geometric constraints (as predicted by the null model) imposed by the narrow span of the gradient, and it is suggested that midelevational zones may represent sink habitats.     

Predicting extinction risk in declining species

What biological attributes predispose species to the risk of extinction? There are many hypotheses but so far there has been no systematic analysis for discriminating between them. Using complete phylogenies of contemporary carnivores and primates, we present, to our knowledge, the first comparative test showing that high trophic level, low population density slow life history and, in particular, small geographical range size are all significantly and independently associated with a high extinction risk in declining species. These traits together explain nearly 50% of the total between-species variation in extinction risk. Much of the remaining variation can be accounted for by external anthropogenic factors that affect species irrespective of their biology.     

Sexual selection and the risk of extinction in birds

The relationship between sexual selection and extinction risk has rarely been investigated. This is unfortunate because extinction plays a key role in determining the patterns of species richness seen in extant clades, which form the basis of comparative studies into the role that sexual selection may play in promoting speciation. We investigate the extent to which the perceived risk of extinction relates to four different estimates of sexual selection in 1030 species of birds. We find no evidence that the number of threatened species is distributed unevenly according to a social mating system, and neither of our two measures of pre-mating sexual selection (sexual dimorphism and dichromatism) was related to extinction risk, after controlling for phylogenetic inertia. However, threatened species apparently experience more intense post-mating sexual selection, measured as testis size, than non-threatened species. These results persisted after including body size as a covariate in the analysis, and became even stronger after controlling for clutch size (two known correlates of extinction risk). Sexual selection may therefore be a double-edged process-promoting speciation on one hand but promoting extinction on the other. Furthermore, we suggest that it is post-mating sexual selection, in particular, that is responsible for the negative effect of sexual selection on clade size. Why this might be is unclear, but the mean population fitness of species with high intensities of post-mating sexual selection may be especially low if costs associated with multiple mating are high or if the selection load imposed by post-mating selection is higher relative to that of pre-mating sexual selection.     

Root quality and decomposition environment,but not tree species richness,drive root decomposition in tropical forests

Plant and Soil - Tropical forests contribute significantly to the global carbon cycle, yet the relative importance of tree diversity on key ecosystem processes such as root decomposition remains...     

Latitudinal gradients in North American avian species richness,turnover rates and extinction probabilities

A decline in species richness moving from equatorial regions to polar regions is a common, but not universal, macroecological pattern. Many studies have focused on this pattern, but few have focused on how the vital rates responsible for species richness patterns, local rates of species extinction and turnover, vary with latitude. We examine patterns of richness, turnover and extinction in North American avian communities inhabiting three ecoregions, using methods that account for failure to detect all species present. We use breeding bird point count data from > 1000 routes in the Breeding Bird Survey collected from 1982 to 2001 to estimate richness, extinction probability and turnover rates. Our analyses differ from others in 1) the use of annual estimates derived at specific locations rather than index data accumulated over numbers of years, 2) the use of estimators that incorporated detection probabilities and 3) a focus on dynamical processes (colonization, extinction) in addition to static patterns (species richness). We find average species richness estimates (48 to 135 species) increasing with latitude for all three regions, contradicting predictions based on the latitudinal diversity gradient. The estimated rates of extinction and turnover declined with latitude across the three ecoregions. We speculate that higher richness might be linked to periods of superabundant food supply in northern areas that support greater numbers of resident and migrant species. Our primary ecological conclusions are that the latitudinal gradient in species richness is reversed for North American birds in the studied ecoregions, and that both local extinction and turnover decrease from southern to northern latitudes. Thus, the vital rates that determine richness show evidence of greater stability and reduced dynamics in northern areas of higher richness. We recommend additional studies examining patterns of colonization, extinction and turnover in communities, that use clearly defined estimators that deal with detection probability.     

Numbers,species richness and equitability of coastal birds at Darwin,Northern Territory

Studies of the species richness and equitability were made of coastal birds at Darwin, Northern Territory, following censusing. A general decrease in numbers and species richness of indigneous and palaearctic migrants occurred in the wet season. Equitability values were depressed at the beginning of the wet season indicating an ecologically disturbed situation Freshwater discharge and its complex mixing patterns in neritic and estuarine water may be responsible for such a disturbance through its effects on the bird's food supply.     

Phylogenetic correlates of extinction risk in mammals: species in older lineages are not at greater risk

Phylogenetic information is becoming a recognized basis for evaluating conservation priorities, but associations between extinction risk and properties of a phylogeny such as diversification rates and phylogenetic lineage ages remain unclear. Limited taxon-specific analyses suggest that species in older lineages are at greater risk. We calculate quantitative properties of the mammalian phylogeny and model extinction risk as an ordinal index based on International Union for Conservation of Nature Red List categories. We test for associations between lineage age, clade size, evolutionary distinctiveness and extinction risk for 3308 species of terrestrial mammals. We show no significant global or regional associations, and three significant relationships within taxonomic groups. Extinction risk increases for evolutionarily distinctive primates and decreases with lineage age when lemurs are excluded. Lagomorph species (rabbits, hares and pikas) that have more close relatives are less threatened. We examine the relationship between net diversification rates and extinction risk for 173 genera and find no pattern. We conclude that despite being under-represented in the frequency distribution of lineage ages, species in older, slower evolving and distinct lineages are not more threatened or extinction-prone. Their extinction, however, would represent a disproportionate loss of unique evolutionary history.     

Livestock settlement affects shrub abundance via plant functional diversity but not species richness in arid environments

Plant Ecology - Recent theoretical and empirical studies have assumed that livestock grazing acts as a biotic filter favouring plant species with functional traits that confer resistance to...     

Litter species traits, but not richness, contribute to carbon and nitrogen dynamics in an alpine meadow on the Tibetan Plateau

Aims

Litter, as afterlife of plants, plays an important role in driving belowground decomposition processes. Here we tested effects of litter species identity and diversity on carbon (C) and nitrogen (N) dynamics during litter decomposition in N-limited alpine meadow soil from the Qinghai–Tibet Plateau.

Methods

We incubated litters of four meadow species, a sedge (“S”, Kobresia humilis), a grass (“G”, Elymus nutans), a herb (“H”, Saussurea superba), and a legume (“L”, Oxytropis falcata), in monoculture and in mixture with meadow soil. CO₂ release was measured 21 times during the incubation, and soil available N and microbial biomass C and N were measured before and after the experiment.

Results

The organic C decay rate did not differ much among soils amended with monocultures or mixtures of litter, except in the H, S, L, and S+H treatments, which had much higher decay rates. Potential decomposable C pools were lowest in the control, highest in the L treatment, and intermediate in the S treatment. Mineralized N was completely immobilized by soil microbes in all treatments except the control, S+L, and S+G+L treatments. Litter mixtures had both additive and non-additive effects on CO₂-C emission (mainly antagonistic effects), net N mineralization (mainly synergistic), and microbial biomass C and N (both). Overall, these parameters were not significantly correlated with litter species richness. Similarly, microbial C or N was not significantly correlated with litter N content or C/N. However, cumulative CO₂-C emission and net N mineralization were positively correlated with litter N content and negatively correlated with litter C/N.

Conclusions

Litter N content and C/N rather than litter species richness drove the release of CO₂-C and net available N in this ecosystem. The antagonistic effects of litter mixtures contributed to a modest release of CO₂-C, but their synergistic effects enhanced net available N. We suggest that in alpine meadow communities, balancing species with high and low N contents will benefit soil carbon sequestration and plant competition for available N with soil microbes.     

Host ecology and life-history traits associated with blood parasite species richness in birds

Identifying host traits associated with the number of different parasite species or strains harboured by a particular host species can have important implications for understanding the impact of parasitism on hosts. We investigated associations between host ecology and life history, and parasite richness and prevalence of the four major avian blood parasite genera. We used an extensive data on blood parasite infections and host ecology in 263 bird species from the Western Palearctic, combining species-specific data with a comparative approach to control for similarity in phenotype among host species due to the effects of common phylogenetic descent. Adult survival rate negatively correlated with the number of parasite species infecting a host species when controlling for similarity due to common descent and body mass. In addition, the prevalence of Haemoproteus, Plasmodium and Leucocytozoon was higher in species harbouring a richer parasite assemblage. These results suggest that the impact on host fitness caused by avian haematozoa may be underestimated in natural populations if the exacerbated virulence associated with exposure to multiple parasites is not taken into account.     

Theoretical habitat templets, species traits, and species richness: birds in the Upper Rhône River and its floodplain

• 1 To test predictions of the river habitat templet and the patch dynamics concept, twenty species traits and the species richness of eighty-one bird species were examined in the context of the spatial – temporal variability of ninety-one sites at Jons, a section of the Upper Rhône River, France.
• 2 The basic information was obtained either from the literature (for species traits) or by observation, then structured by a fuzzy coding technique, and examined using multivariate analyses.
• 3 The relationships between species traits separated three groups of birds: (i) large species that are long lived, have long breeding cycles, and use open sites to feed, breed, and sing (e.g. Podicipidae, Laridae); (ii) medium-sized species with intermediate longevities and breeding cycles that use less open sites (e.g. Columbidae, Corvidae); and (iii) small species that are short lived, have short breeding cycles, and use closed sites (e.g. Sylviidae).
• 4 The distribution of birds in the floodplain habitats of the river was closely related to the spatial–temporal variability of sites.
• 5 No trends in species traits were observed along a gradient of spatial–temporal variability of the sites.
• 6 Species richness of birds was relatively constant over the gradient of spatial–temporal variability of the ninety-one sites, but decreased at low spatial and high temporal variability because of human activities and vegetation changes that occurred at these sites.
• 7 These observations on species traits and richness were related to the high mobility of birds (which is a scale phenomenon) and the high intercorrelation between parameters used to determine the spatial and temporal variability of the sites (which makes separation of the spatial from the temporal variability impossible).

     

Voice pitch predicts electability,but does not signal leadership ability

Voice pitch, the perceived “highness” or “lowness” of a voice, influences how humans perceive and treat each other in various ways. One example is the selection of leaders. A growing number of studies, both experimental and observational, show that individuals with lower-pitched voices are more likely to win elected office. This leads to the yet untested question of whether individuals with lower voices are actually better leaders. That is, is voice pitch a reliable signal of leadership ability? Here we address this question with an observational study of the vocal pitch and leadership ability of elected officials, and an experiment where subjects were asked to respond to persuasive political policy statements made by speakers with different pitched voices. Both studies lead to the same conclusion: voice pitch does not correlate with leadership ability.