Evaluating the population‐level impact of an invasive species,Ring‐necked Parakeet Psittacula krameri,on native avifauna

The introduction of exotic species to ecosystems can have severe consequences for populations of native organisms, but logistical limitations and shortage of historical data often hinder attempts to quantify the ecological implications of such relationships. The establishment and rapid expansion of Ring‐necked Parakeets Psittacula krameri in England therefore presents a rare opportunity to apply novel analytical methods to existing extensive national bird monitoring data from the UK Breeding Bird Survey for an invasive species. A previous study from Belgium suggests that Ring‐necked Parakeets have the potential to reduce the abundance of Eurasian Nuthatch Sitta europaea through competition for nesting cavities. Our analysis provides no evidence for a significant impact through competition on Nuthatch populations or those of any other cavity‐nesting species within the Parakeet’s current range in the UK. However, we cannot exclude the possibility that competitive exclusion could be occurring at a minority of sites at which availability of nest cavities is limiting. This may yet have significant implications for future conflict if Parakeets continue to increase in numbers and range.     

The demographic effects of functional traits: an integral projection model approach reveals population‐level consequences of reproduction‐defence trade‐offs

Quantitatively linking individual variation in functional traits to demography is a necessary step to advance our understanding of trait‐based ecological processes. We constructed a population model for Asclepias syriaca to identify how functional traits affect vital rates and population growth and whether trade‐offs in chemical defence and demography alter population growth. Plants with higher foliar cardenolides had lower fibre, cellulose and lignin levels, as well as decreased sexual and clonal reproduction. Average cardenolide concentrations had the strongest effect on population growth. In both the sexual and clonal pathway, the trade‐off between reproduction and defence affected population growth. We found that both increasing the mean of the distribution of individual plant values for cardenolides and herbivory decreased population growth. However, increasing the variance in both defence and herbivory increased population growth. Functional traits can impact population growth and quantifying individual‐level variation in traits should be included in assessments of population‐level processes.     

Individual‐ and population‐level personalities in a floriphilic katydid

Behaviour, including personality, informs us about the response of animals towards their changing environment. Despite the widespread occurrence of florivorous insects and the important but often underrated ecological roles that they play, the study of florivore behaviour is neglected relative to that of pollinators and other herbivores. Specifically, we do not know how different personality types can develop among florivores and enable them to persist in habitats with an ephemeral and dynamic availability of food resources. To address this knowledge gap, we investigated the following questions: whether the (a) inter‐individual differences of exploration and boldness are consistent; (b) inter‐population differences of exploration and boldness are consistent; (c) exploration and boldness are correlated. We collected individuals of the polyphagous floriphilic katydid, Phaneroptera brevis from four populations from wasteland sites in Singapore and performed a personality assay conducted in an insectary to investigate the exploratory and boldness levels of the individuals and populations. The major novel finding was that the floriphilic P. brevis katydids exhibit population‐level personality types for boldness, but not for exploration. Some katydid individuals were consistently more exploratory and bolder than other individuals. However, contrary to our predictions, we did not find any evidence of behavioural syndromes in the katydid individuals, as the boldness level for individuals was not significantly correlated with exploration for individuals. This suggests that an individual which is more exploratory may not be equally keen to take risks and consume novel food that it encounters. Our findings also suggest that boldness and exploration are linked to ecologically important behaviours, but more studies are needed to better understand population‐level personality and how and why natural selection may favour the evolution of personality in certain populations.     

Comparative genetic structure and demographic history in endemic galapagos weevils

The challenge of maintaining genetic diversity within populations can be exacerbated for island endemics if they display population dynamics and behavioral attributes that expose them to genetic drift without the benefits of gene flow. We assess patterns of the genetic structure and demographic history in 27 populations of 9 species of flightless endemic Galápagos weevils from 9 of the islands and 1 winged introduced close relative. Analysis of mitochondrial DNA reveals a significant population structure and moderately variable, though demographically stable, populations for lowland endemics (F(ST) = 0.094-0.541; π: 0.014-0.042; Mismatch P = 0.003-0.026; and D((Tajima)) = -0.601 to 1.203), in contrast to signals of past contractions and expansions in highland specialists on 2 islands (Mismatch P = 0.003-0.026 and D((Tajima)) = -0.601 to 1.203). We interpret this series of variable and highly structured population groups as a system of long-established, independently founded island units, where structuring could be a signal of microallopatric differentiation due to patchy host plant distribution and poor dispersal abilities. We suggest that the severe reduction and subsequent increase of a suitably moist habitat that accompanied past climatic variation could have contributed to the observed population fluctuations in highland specialists. We propose the future exploration of hybridization between the introduced and highland endemic species on Santa Cruz, especially given the expansion of the introduced species into the highlands, the sensitivity to past climatic variation detected in highland populations, and the potentially threatened state of single-island endemics.     

Impacts of an invasive ant species on roosting behavior of an island endemic flying‐fox

Introduced species can cause major disruptions to ecosystems, particularly on islands. On Christmas Island, the invasive yellow crazy ant (Anoplolepis gracilipes) has detrimental impacts on many animals ranging from the iconic red crabs (Gecarcoidea natalis) to the Christmas Island Thrush (Turdus poliocephalus erythropleurus). However, the full extent of its effects on the island's fauna is not yet known. In this study, we investigated the impact of the yellow crazy ants on the island's last native mammal: the Christmas Island flying‐fox (Pteropus natalis). This species has been described as a keystone species, but has recently experienced substantial population decline to the extent that it is now listed as Critically Endangered. We examined the impacts of the yellow crazy ants on the roosting behavior of the Christmas Island flying‐fox, and on its local and island‐wide distribution patterns. We showed that the crazy ants increased behaviors in the flying‐foxes that were associated with avoidance of noxious stimuli and decreased behaviors associated with resting. Roost tree selection and roost site location were not related to variation in the abundance of crazy ants on the island. Our results indicate that the crazy ants interfere with the activity budgets of the flying‐foxes. However, the flying‐foxes failed to relocate to ant‐free roost trees or roost sites when confronted with the noxious ant, suggesting that the flying‐foxes are either not sufficiently disturbed to override strong cultural attachment to roosts, or, are behaving maladaptively due to ecological naïveté.     

Evolutionary history shapes the association between developmental instability and population‐level genetic variation in three‐spined sticklebacks

Developmental instability (DI) is the sensitivity of a developing trait to random noise and can be measured by degrees of directionally random asymmetry [fluctuating asymmetry (FA)]. FA has been shown to increase with loss of genetic variation and inbreeding as measures of genetic stress, but associations vary among studies. Directional selection and evolutionary change of traits have been hypothesized to increase the average levels of FA of these traits and to increase the association strength between FA and population‐level genetic variation. We test these two hypotheses in three‐spined stickleback (Gasterosteus aculeatus L.) populations that recently colonized the freshwater habitat. Some traits, like lateral bone plates, length of the pelvic spine, frontal gill rakers and eye size, evolved in response to selection regimes during colonization. Other traits, like distal gill rakers and number of pelvic fin rays, did not show such phenotypic shifts. Contrary to a priori predictions, average FA did not systematically increase in traits that were under presumed directional selection, and the increases observed in a few traits were likely to be attributable to other factors. However, traits under directional selection did show a weak but significantly stronger negative association between FA and selectively neutral genetic variation at the population level compared with the traits that did not show an evolutionary change during colonization. These results support our second prediction, providing evidence that selection history can shape associations between DI and population‐level genetic variation at neutral markers, which potentially reflect genetic stress. We argue that this might explain at least some of the observed heterogeneities in the patterns of asymmetry.     

Demographic and population‐genetic tests provide mixed support for the abundant centre hypothesis in the endemic plant Leavenworthia stylosa

The abundant centre hypothesis (ACH) assumes that population abundance, population size, density and per‐capita reproductive output should peak at the centre of a species' geographic range and decline towards the periphery. Increased isolation among and decreased reproductive output within edge populations should reduce within‐population genetic diversity and increase genetic differentiation among edge relative to central populations. The ACH also predicts asymmetrical gene flow, with net movement of migrants from the centre to edges. We evaluated these ecological assumptions and population‐genetic predictions in the endemic flowering plant Leavenworthia stylosa. Although populations were more spatially isolated near range edges, the geographic centre was surrounded by and not coincident with areas of peak population abundance, and plant density increased towards range edges. Per‐capita seed number was not associated with distance to the range centre, but seed number/m² increased near range edges. In support of ACH predictions, allelic diversity at 12 microsatellite loci declined with distance from the range centre, and pairwise F_ST values were higher between edge populations than between central populations. Coalescent analyses confirmed that gene flow was most infrequent between edge populations, but there was not an asymmetric pattern of gene flow predicted by the ACH. This study shows that among‐population demographic variability largely did not support the ACH, while patterns of genetic diversity, differentiation and gene flow were generally consistent with its predictions. Such mixed support has frequently been observed in tests of the ACH and raises concerns regarding the generality of this hypothesis for species range limits.     

Influence of environmental heterogeneity on genetic diversity and structure in an endemic southern Californian oak

Understanding how specific environmental factors shape gene flow while disentangling their importance relative to the effects of geographical isolation is a major question in evolutionary biology and a specific goal of landscape genetics. Here, we combine information from nuclear microsatellite markers and ecological niche modelling to study the association between climate and spatial genetic structure and variability in Engelmann oak (Quercus engelmannii), a wind-pollinated species with high potential for gene flow. We first test whether genetic diversity is associated with climatic niche suitability and stability since the Last Glacial Maximum (LGM). Second, we use causal modelling to analyse the potential influence of climatic factors (current and LGM niche suitability) and altitude in the observed patterns of genetic structure. We found that genetic diversity is negatively associated with local climatic stability since the LGM, which may be due to higher immigration rates in unstable patches during favourable climatic periods and/or temporally varying selection. Analyses of spatial genetic structure revealed the presence of three main genetic clusters, a pattern that is mainly driven by two highly differentiated populations located in the northern edge of the species distribution range. After controlling for geographic distance, causal modelling analyses showed that genetic relatedness decreases with the environmental divergence among sampling sites estimated as altitude and current and LGM niche suitability. Natural selection against nonlocal genotypes and/or asynchrony in reproductive phenology may explain this pattern. Overall, this study suggests that local environmental conditions can shape patterns of genetic structure and variability even in species with high potential for gene flow and relatively small distribution ranges.     

Islands within an island: Population genetic structure of the endemic Sardinian newt,Euproctus platycephalus

The identification of historic and contemporary barriers to dispersal is central to the conservation of endangered amphibians, but may be hindered by their complex life history and elusive nature. The complementary information generated by mitochondrial (mtDNA) and microsatellite markers generates a valuable tool in elucidating population structure and the impact of habitat fragmentation. We applied this approach to the study of an endangered montane newt, Euproctus platycephalus. Endemic to the Mediterranean island of Sardinia, it is threatened by anthropogenic activity, disease, and climate change. We have demonstrated a clear hierarchy of structure across genetically divergent and spatially distinct subpopulations. Divergence between three main mountain regions dominated genetic partitioning with both markers. Mitochondrial phylogeography revealed a deep division dating to ca. 1 million years ago (Mya), isolating the northern region, and further differentiation between the central and southern regions ca. 0.5 Mya, suggesting an association with Pleistocene severe glacial oscillations. Our findings are consistent with a model of southward range expansion during glacial periods, with postglacial range retraction to montane habitat and subsequent genetic isolation. Microsatellite markers revealed further strong population structure, demonstrating significant divergence within the central region, and partial differentiation within the south. The northern population showed reduced genetic diversity. Discordance between mitochondrial and microsatellite markers at this scale indicated a further complexity of population structure, in keeping with male‐biased dispersal and female philopatry. Our study underscores the need to elucidate cryptic population structure in the ecology and conservation strategies for endangered island‐restricted amphibians, especially in the context of disease and climate change.     

Age‐specific,population‐level pedigree of wild black bears provides insights into reproduction,paternity, and maternal effects on offspring apparent survival

Wildlife pedigrees provide insights into ecological and evolutionary processes. DNA obtained from noninvasively collected hair is often used to determine individual identities for pedigrees and other genetic analyses. However, detection rates associated with some noninvasive DNA studies can be relatively low, and genetic data do not provide information on individual birth year. Supplementing hair DNA stations with video cameras should increase the individual detection rate, assuming accurate identification of individuals via video data. Video data can also provide birth year information for individuals captured as young of the year, which can enrich population‐level pedigrees. We placed video cameras at hair stations and combined genetic and video data to reconstruct an age‐specific, population‐level pedigree of wild black bears during 2010–2020. Combining individual birth year with mother–offspring relatedness, we also estimated litter size, interlitter interval, primiparity, and fecundity. We used the Cormack‐Jolly‐Seber model in Program Mark to evaluate the effect of maternal identity on offspring apparent survival. We compared model rankings of apparent survival and parameter estimates based on combined genetic and video data with those based on only genetic data. We observed 42 mother–offspring relationships. Of these, 21 (50%) would not have been detected had we used hair DNA alone. Moreover, video data allowed for the cub and yearling age classes to be determined. Mean annual fecundity was 0.42 (95% CI: 0.27, 0.56). Maternal identity influenced offspring apparent survival, where offspring of one mother experienced significantly lower apparent survival (0.39; SE = 0.15) than that of offspring of four other mothers (0.89–1.00; SE = 0.00–0.06). We video‐documented cub abandonment by the mother whose offspring experienced low apparent survival, indicating individual behaviors (e.g., maternal care) may scale up to affect population‐level parameters (e.g., cub survival). Our findings provide insights into evolutionary processes and are broadly relevant to wildlife ecology and conservation.     

Age at maturity in wild baboons: genetic, environmental and demographic influences

The timing of early life-history events, such as sexual maturation and first reproduction, can greatly influence variation in individual fitness. In this study, we analysed possible sources of variation underlying different measures of age at social and physical maturation in wild baboons in the Amboseli basin, Kenya. The Amboseli baboons are a natural population primarily comprised of yellow baboons (Papio cynocephalus) that occasionally hybridize with anubis baboons (Papio anubis) from outside the basin. We found that males and females differed in the extent to which various factors influenced their maturation. Surprisingly, we found that male maturation was most strongly related to the proportion of anubis ancestry revealed by their microsatellite genotypes: hybrid males matured earlier than yellow males. In contrast, although hybrid females reached menarche slightly earlier than yellow females, maternal rank and the presence of maternal relatives had the largest effects on female maturation, followed by more modest effects of group size and rainfall. Our results indicate that a complex combination of demographic, genetic, environmental, and maternal effects contribute to variation in the timing of these life-history milestones.     

Overcoming Allee effects through evolutionary,genetic, and demographic rescue

Despite the amplified threats of extinction facing small founder populations, successful colonization sometimes occurs, bringing devastating ecological and economic consequences. One explanation may be rapid evolution, which can increase mean fitness in populations declining towards extinction, permitting persistence and subsequent expansion. Such evolutionary rescue may be particularly important, given Allee effects. When a population is introduced at low density, individuals often experience a reduction in one or more components of fitness due to novel selection pressures that arise from diminished intraspecific interactions and positive density dependence (i.e. component Allee effects). A population can avoid extinction if it can adapt and recover on its own (i.e. evolutionary rescue), or if additional immigration sustains the population (i.e. demographic rescue) or boosts its genetic variation that facilitates adaptation (i.e. genetic rescue). These various forms of rescue have often been invoked as possible mechanisms for specific invasions, but their relative importance to invasion is not generally understood. Within a spatially explicit modelling framework, we consider the relative impact of each type of rescue on the probability of successful colonization, when there is evolution of a multi-locus quantitative trait that influences the strength of component Allee effects. We demonstrate that when Allee effects are important, the effect of demographic rescue via recurrent immigration overall provides the greatest opportunity for success. While highlighting the role of evolution in the invasion process, we underscore the importance of the ecological context influencing the persistence of small founder populations.     

Reduced genetic diversity and increased reproductive isolation follow population‐level loss of larval dispersal in a marine gastropod

Population‐level consequences of dispersal ability remain poorly understood, especially for marine animals in which dispersal is typically considered a species‐level trait governed by oceanographic transport of microscopic larvae. Transitions from dispersive (planktotrophic) to nondispersive, aplanktonic larvae are predicted to reduce connectivity, genetic diversity within populations, and the spatial scale at which reproductive isolation evolves. However, larval dimorphism within a species is rare, precluding population‐level tests. We show the sea slug Costasiella ocellifera expresses both larval morphs in Florida and the Caribbean, regions with divergent mitochondrial lineages. Planktotrophy predominated at 11 sites, 10 of which formed a highly connected and genetically diverse Caribbean metapopulation. Four populations expressed mainly aplanktonic development and had markedly reduced connectivity, and lower genetic diversity at one mitochondrial and six nuclear loci. Aplanktonic dams showed partial postzygotic isolation in most interpopulation crosses, regardless of genetic or geographic distance to the sire's source, suggesting that outbreeding depression affects fragmented populations. Dams from genetically isolated and neighboring populations also exhibited premating isolation, consistent with reinforcement contingent on historical interaction. By increasing self‐recruitment and genetic drift, the loss of dispersal may thus initiate a feedback loop resulting in the evolution of reproductive isolation over small spatial scales in the sea.     

Partitioning the sources of demographic variation reveals density‐dependent nest predation in an island bird population

Ecological factors often shape demography through multiple mechanisms, making it difficult to identify the sources of demographic variation. In particular, conspecific density can influence both the strength of competition and the predation rate, but density‐dependent competition has received more attention, particularly among terrestrial vertebrates and in island populations. A better understanding of how both competition and predation contribute to density‐dependent variation in fecundity can be gained by partitioning the effects of density on offspring number from its effects on reproductive failure, while also evaluating how biotic and abiotic factors jointly shape demography. We examined the effects of population density and precipitation on fecundity, nest survival, and adult survival in an insular population of orange‐crowned warblers (Oreothlypis celata) that breeds at high densities and exhibits a suite of traits suggesting strong intraspecific competition. Breeding density had a negative influence on fecundity, but it acted by increasing the probability of reproductive failure through nest predation, rather than through competition, which was predicted to reduce the number of offspring produced by successful individuals. Our results demonstrate that density‐dependent nest predation can underlie the relationship between population density and fecundity even in a high‐density, insular population where intraspecific competition should be strong.     

Drawing ecological inferences from coincident patterns of population‐ and community‐level biodiversity

Biodiversity is comprised of genetic and phenotypic variation among individual organisms, which might belong to the same species or to different species. Spatial patterns of biodiversity are of central interest in ecology and evolution for several reasons: to identify general patterns in nature (e.g. species–area relationships, latitudinal gradients), to inform conservation priorities (e.g. identifying hotspots, prioritizing management efforts) and to draw inferences about processes, historical or otherwise (e.g. adaptation, the centre of origin of particular clades). There are long traditions in ecology and evolutionary biology of examining spatial patterns of biodiversity among species (i.e. in multispecies communities) and within species, respectively, and there has been a recent surge of interest in studying these two types of pattern simultaneously. The idea is that examining both levels of diversity can materially advance the above‐stated goals and perhaps lead to entirely novel lines of inquiry. Here, we review two broad categories of approach to merging studies of inter‐ and intraspecific variation: (i) the study of phenotypic trait variation along environmental gradients and (ii) the study of relationships between patterns of molecular genetic variation within species and patterns of distribution and diversity across species. For the latter, we report a new meta‐analysis in which we find that correlations between species diversity and genetic diversity are generally positive and significantly stronger in studies with discrete sampling units (e.g. islands, lakes, forest fragments) than in studies with nondiscrete sampling units (e.g. equal‐area study plots). For each topic, we summarize the current state of knowledge and key future directions.