Search

A single adverse environment event can threaten the survival of small‐ranged species while random fluctuations in population size increase the extinction risk of less‐abundant species. The abundance–range‐size relationship (ARR) is usually positive, which means that smaller‐ranged species are often of low abundance and might face both problems simultaneously.The ARR has been reported to be negative on tropical islands, perhaps allowing endemic species in such environments to remain extant. But there is a need to understand how endemism and land‐use interact to shape ARR.Using 41 highly replicated transects along the full elevational gradient of Sri Lanka, we determined the following: (a) the direction of ARR, (b) if endemism affects ARR and (c) if land‐use (rainforest, buffer and agriculture) changes ARR differently for endemics and non‐endemics. Additionally, (d) we identified endemics that had both lower abundances and smaller range sizes, and ranked them from most threatened (specific to rainforests) to least threatened using a weighted‐interaction nestedness estimator.(a) We found a positive relationship between species abundances and range size. This positive ARR was maintained among endemic and non‐endemic species, across land‐use types and at local and regional scales. (b) The ARR interacted with endemicity and land‐use. Endemics with smaller range sizes had higher abundances than non‐endemics, and particularly higher in rainforests compared to agriculture. In contrast, species with larger range sizes had similar abundances across endemicity and land‐use categories. Many endemics with smaller range sizes are globally threatened; therefore, higher abundances may buffer them from extinction risks. (c) Nine (29%) endemics had both below average abundance and elevational range size. The nestedness estimator ranked the endemics Sri Lanka Whistling Thrush Myophonus blighi, Red‐faced Malkoha Phaenicophaeus pyrrhocephalus, Sri Lanka Thrush Zoothera imbricata and White‐faced Starling Sturnornis albofrontus as the four most vulnerable species to local extinction risk, which corresponds to their global extinction risk.We demonstrate that ARR can be positive on tropical islands, but it is influenced by endemism and land‐use. Examining shifts in ARR is not only important to understand community dynamics but can also act as a tool to inform managers about species that require monitoring programmes. [ABSTRACT FROM AUTHOR]

Anthropogenic activities influence ongoing selective regimes leading to changes in phenotypic variation of plants and animals. The reduction of phenotypic variation may decrease populations' ability to cope with environmental changes. To counteract the increasing risk of extinction of affected populations, it is important to rescue intraspecific variability, assuring higher success of establishment and persistence under global changes.We evaluated whether it is possible to revert phenotypic changes caused by humans using as study case a bird‐dispersed palm that presents seed size reduction due to defaunation of large‐gaped frugivores. We investigated how defaunation changes the seed size profile of each population by evaluating the coefficient of variation, mean and percentage of large phenotypes of produced and dispersed seed sizes. Simple theoretical models were used to simulate the success of two restoration strategies: (a) direct reintroduction of missing phenotypes that were originally found in the species and (b) reintroduction of large‐bodied frugivores to restore the ecological function of large‐seed dispersal. Here we discuss the importance of rescuing phenotype states in restoration strategies.We found that defaunation changes the seed size profile by reducing the size of produced and dispersed seeds. By adding missing phenotypes one time, population mean seed size decreased back to phenotypically depauperated scenarios in eight generations. Conversely, large seed sizes could be rescued in approximately five generations after seed dispersal processes generated by large seed dispersers were re‐established.To rescue and sustain phenotypes such as large seed sizes in palm populations is necessary to restore the seed dispersal processes by large frugivores or add missing phenotypes continuously over time. The restoration of the seed dispersal processes by large frugivores has additional value over seed addition because it would benefit other bird‐dispersed species and, therefore, may be crucial to face ongoing global change scenarios.Synthesis and applications. Defaunation leads to character displacement within decades, having impact on populations, species and ecosystems. To prevent species extinction is paramount that phenotype variation is preserved. We propose the inclusion of phenotype restoration of wild populations as a goal for restoration framework. [ABSTRACT FROM AUTHOR]

The usage of invasive tagging methods to assess lizard populations has often been criticised, due to the potential negative effects of marking, which possibly cause increased mortality or altered behaviour. The development of safe, less invasive techniques is essential for improved ecological study and conservation of lizard populations. In this study, we describe a photographic capture-recapture (CR) technique for estimating Draco dussumieri (Agamidae) populations. We used photographs of the ventral surface of the patagium to identify individuals. To establish that the naturally occurring blotches remained constant through time, we compared capture and recapture photographs of 45 pen-marked individuals after a 30 day interval. No changes in blotches were observed and individual lizards could be identified with 100% accuracy. The population density of D. dussumieri in a two hectare areca-nut plantation was estimated using the CR technique with ten sampling occasions over a ten day period. The resulting recapture histories for 24 individuals were analysed using population models in the program CAPTURE. All models indicated that nearly all individuals were captured. The estimated probability for capturing D. dussumieri on at least one occasion was 0.92 and the estimated population density was 13±1.65 lizards/ha. Our results demonstrate the potential for applying CR to population studies in gliding lizards (Draco spp.) and other species with distinctive markings. [ABSTRACT FROM AUTHOR]

The usage of invasive tagging methods to assess lizard populations has often been criticised, due to the potential negative effects of marking, which possibly cause increased mortality or altered behaviour. The development of safe, less invasive techniques is essential for improved ecological study and conservation of lizard populations. In this study, we describe a photographic capture-recapture (CR) technique for estimating Draco dussumieri (Agamidae) populations. We used photographs of the ventral surface of the patagium to identify individuals. To establish that the naturally occurring blotches remained constant through time, we compared capture and recapture photographs of 45 pen-marked individuals after a 30 day interval. No changes in blotches were observed and individual lizards could be identified with 100% accuracy. The population density of D. dussumieri in a two hectare areca-nut plantation was estimated using the CR technique with ten sampling occasions over a ten day period. The resulting recapture histories for 24 individuals were analysed using population models in the program CAPTURE. All models indicated that nearly all individuals were captured. The estimated probability for capturing D. dussumieri on at least one occasion was 0.92 and the estimated population density was 13±1.65 lizards/ha. Our results demonstrate the potential for applying CR to population studies in gliding lizards (Draco spp.) and other species with distinctive markings. [ABSTRACT FROM AUTHOR]

Birds, bats and ants are recognised as significant arthropod predators. However, empirical studies reveal inconsistent trends in their relative roles in top-down control across strata. Here, we describe the differences between forest strata in the separate effects of birds, bats and ants on arthropod densities and their cascading effects on plant damage. We implemented a factorial design to exclude vertebrates and ants in both the canopy and understorey. Additionally, we separately excluded birds and bats from the understorey using diurnal and nocturnal exclosures. At the end of the experiments, we collected all arthropods and assessed herbivory damage. Arthropods responded similarly to predator exclusion across forest strata, with a density increase of 81% on trees without vertebrates and 53% without both vertebrates and ants. Additionally, bird exclusion alone led to an 89% increase in arthropod density, while bat exclusion resulted in a 63% increase. Herbivory increased by 42% when vertebrates were excluded and by 35% when both vertebrates and ants were excluded. Bird exclusion alone increased herbivory damage by 28%, while the exclusion of bats showed a detectable but non-significant increase (by 22%). In contrast, ant exclusion had no significant effect on arthropod density or herbivory damage across strata. Our results reveal that the effects of birds and bats on arthropod density and herbivory damage are similar between the forest canopy and understorey in this temperate forest. In addition, ants were not found to be significant predators in our system. Furthermore, birds, bats and ants appeared to exhibit antagonistic relationships in influencing arthropod density. These findings highlight, unprecedentedly, the equal importance of birds and bats in maintaining ecological balance across different strata of a temperate forest., (© 2024 The Author(s). Journal of Animal Ecology © 2024 British Ecological Society.)

Owls have the potential to be keystone species for conservation in fragmented landscapes, as the absence of these predators could profoundly change community structure. Yet few studies have examined how whole communities of owls respond to fragmentation, especially in the tropics. When evaluating the effect of factors related to fragmentation, such as fragment area and distance to the edge, on these birds, it is also important in heterogeneous landscapes to ask how 'location factors' such as the topography, vegetation and soil of the fragment predict their persistence. In Xishuangbanna, southwest China, we established 43 transects (200 m×60 m) within 20 forest fragments to sample nocturnal birds, both visually and aurally. We used a multimodel inference approach to identify the factors that influence owl species richness, and generalized linear mixed models to predict the occurrence probabilities of each species. We found that fragmentation factors dominated location factors, with larger fragments having more species, and four of eight species were significantly more likely to occur in large fragments. Given the potential importance of these birds on regulating small mammal and other animal populations, and thus indirectly affecting seed dispersal, we suggest further protection of large fragments and programs to increase their connectivity to the remaining smaller fragments.