Understanding demographic limiting factors to species recovery: Nest-site suitability and breeding ecology of Phelsuma guentheri on Round Island, Mauritius

The island of Mauritius in the Mascarenes has already suffered high levels of extinction, and habitat destruction and invasive alien species have pushed many of the remaining endemic species to the brink of extinction. Round Island, a small island northeast of Mauritius, is home to remnant populations of several reptile species that were once distributed across Mauritius. One of the most threatened of these is Günther’s gecko Phelsuma guentheri, where despite extensive management efforts, population size remains small and below expectation. We identify determinants of nest-site suitability across Round Island, and examine whether suitable nest sites are a limiting factor for the abundance of P. guentheri. Over one breeding season, we recorded and monitored a high number (269) of nest sites harbouring a total of 1475 eggs. We used the number of eggs at each nest, and the hatching success as proxies for nest-site suitability. To study the reproductive behaviour of P. guentheri, we installed trail cameras at three nest sites. We did not find the expected high frequency of use of hardwood trees as nest sites, as found on Ile aux Aigrettes to the southeast of Mauritius, probably because hardwood trees are still relatively sparse and small on Round Island. Instead, the endemic palm Latania loddigesii was the most used nest sites, harbouring 78.8% of all nests with 56.3% of all eggs. Hatching success was high for palm nest sites (90.6%), rock surfaces (91.8%), and on the endemic screw pine Pandanus vandermeeschii (96%), rates that are similar to that reported from hardwood trees on Ile aux Aigrettes (~90%). Communal nesting occurred on all substrates, with up to five individuals using the same nest site. Egg-laying took place at dusk or at night, lasting around 30 min, whereas hatching occurred mostly during the day, lasting 2–107 min. Females laid eggs every 34 days on average, and produced up to four clutches of 1–2 eggs each within the season. We conclude that P. guentheri does not suffer from nest site limitation on Round Island, and that reproductive success is high in terms of both numbers of eggs laid and hatching success, likely due to ongoing habitat restoration. Further research is needed to investigate the factors inhibiting abundance and distribution of P. guentheri on Round Island

New universal ITS2 primers for high-resolution herbivory analyses using DNA metabarcoding in both tropical and temperate zones

DNA metabarcoding is a rapidly growing technique for obtaining detailed dietary information. Current metabarcoding methods for herbivory, using a single locus, can lack taxonomic resolution for some applications. We present novel primers for the second internal transcribed spacer of nuclear ribosomal DNA (ITS2) designed for dietary studies in Mauritius and the UK, which have the potential to give unrivalled taxonomic coverage and resolution from a short-amplicon barcode. In silico testing used three databases of plant ITS2 sequences from UK and Mauritian floras (native and introduced) totalling 6561 sequences from 1790 species across 174 families. Our primers were well-matched in silico to 88% of species, providing taxonomic resolution of 86.1%, 99.4% and 99.9% at the species, genus and family levels, respectively. In vitro, the primers amplified 99% of Mauritian (n = 169) and 100% of UK (n = 33) species, and co-amplified multiple plant species from degraded faecal DNA from reptiles and birds in two case studies. For the ITS2 region, we advocate taxonomic assignment based on best sequence match instead of a clustering approach. With short amplicons of 187–387 bp, these primers are suitable for metabarcoding plant DNA from faecal samples, across a broad geographic range, whilst delivering unparalleled taxonomic resolution

Avoiding bias in estimates of population size for translocation management

Mark–recapture surveys are commonly used to monitor translocated populations globally. Data gathered are then used to estimate demographic parameters, such as abundance and survival, using Jolly–Seber (JS) models. However, in translocated populations initial population size is known and failure to account for this may bias parameter estimates, which are important for informing conservation decisions during population establishment. Here, we provide methods to account for known initial population size in JS models by incorporating a separate component likelihood for translocated individuals, using a maximum‐likelihood estimation, with models that can be fitted using either R or MATLAB. We use simulated data and a case study of a threatened lizard species with low capture probability to demonstrate that unconstrained JS models may overestimate the size of translocated populations, especially in the early stages of post‐release monitoring. Our approach corrects this bias; we use our simulations to demonstrate that overestimates of population size between 78% and 130% can occur in the unconstrained JS models when the detection probability is below 0.3 compared to 1%–8.9% for our constrained model. Our case study did not show an overestimate; however accounting for the initial population size greatly reduced error in all parameter estimates and prevented boundary estimates. Adopting the corrected JS model for translocations will help managers to obtain more robust estimates of the population sizes of translocated animals, better informing future management including reinforcement decisions, and ultimately improving translocation success

Observational and metabarcoding approaches reveal the ecology, natural history and conservation status of Scolopendra abnormis, a threatened centipede endemic to Mauritius

The Serpent Island centipede Scolopendra abnormis is a threatened centipede species found on only 2 small islands in the Indian Ocean: Round Island, located 22.5 km northeast of Mauritius, and Serpent Island, 4 km northwest of Round Island. Current understanding of its ecology is based on limited direct observations from 30 yr ago. Round Island has since undergone significant habitat restoration. Hyperabundant non-native ants are also present, which may impact centipede nesting behaviour, ecology, and survival. Recent methodological advances, such as high-throughput sequencing of dietary DNA, can extend our understanding of invertebrate ecology and provide data complementary to direct observation. Using a combination of dietary metabarcoding and observational approaches, we provide new insights into the ecology and natural history of this threatened invertebrate predator. S. abnormis nest most consistently in the root network found beneath endemic Pandanus vandermeeschii trees. They are also found in areas with good soil cover, herbaceous growth, and areas of bare rock slab. Only 4 of 43 centipedes in this study were found near an ant foraging trail, which may have significant implications for S. abnormis nesting habits. These centipedes primarily consume insect prey (particularly taxa within Lepidoptera, Hymenoptera, Diptera), irrespective of centipede body size. A quarter of centipedes also consumed endemic lizards. We also found marked differences in diet composition between wet and dry seasons arising from the changing availability of prey. We provide additional natural history observations and conclude by suggesting conservation actions that would help better understand and safeguard S. abnormis populations

Individual consistency in migration strategies of a tropical seabird, the Round Island petrel

Background: In migratory species, the extent of within- and between-individual variation in migratory strategies can influence potential rates and directions of responses to environmental changes. Quantifying this variation requires tracking of many individuals on repeated migratory journeys. At temperate and higher latitudes, low levels of within-individual variation in migratory behaviours are common and may reflect repeated use of predictable resources in these seasonally-structured environments. However, variation in migratory behaviours in the tropics, where seasonal predictability of food resources can be weaker, remains largely unknown. Methods: Round Island petrels (Pterodroma sp.) are tropical, pelagic seabirds that breed all year round and perform long-distance migrations. Using multi-year geolocator tracking data from 62 individuals between 2009 and 2018, we quantify levels of within- and between-individual variation in non-breeding distributions and timings. Results: We found striking levels of between-individual variation in at-sea movements and timings, with non-breeding migrations to different areas occurring across much of the Indian Ocean and throughout the whole year. Despite this, repeat-tracking of individual petrels revealed remarkably high levels of spatial and temporal consistency in within-individual migratory behaviour, particularly for petrels that departed at similar times in different years and for those departing in the austral summer. However, while the same areas were used by individuals in different years, they were not necessarily used at the same times during the non-breeding period. Conclusions: Even in tropical systems with huge ranges of migratory routes and timings, our results suggest benefits of consistency in individual migratory behaviours. Identifying the factors that drive and maintain between-individual variation in migratory behaviour, and the consequences for breeding success and survival, will be key to understanding the consequences of environmental change across migratory ranges

Individual consistency in migration strategies of a tropical seabird, the Round Island petrel

Background: In migratory species, the extent of within- and between-individual variation in migratory strategies can influence potential rates and directions of responses to environmental changes. Quantifying this variation requires tracking of many individuals on repeated migratory journeys. At temperate and higher latitudes, low levels of within-individual variation in migratory behaviours are common and may reflect repeated use of predictable resources in these seasonally-structured environments. However, variation in migratory behaviours in the tropics, where seasonal predictability of food resources can be weaker, remains largely unknown. Methods: Round Island petrels (Pterodroma sp.) are tropical, pelagic seabirds that breed all year round and perform long-distance migrations. Using multi-year geolocator tracking data from 62 individuals between 2009 and 2018, we quantify levels of within- and between-individual variation in non-breeding distributions and timings. Results: We found striking levels of between-individual variation in at-sea movements and timings, with non-breeding migrations to different areas occurring across much of the Indian Ocean and throughout the whole year. Despite this, repeat-tracking of individual petrels revealed remarkably high levels of spatial and temporal consistency in within-individual migratory behaviour, particularly for petrels that departed at similar times in different years and for those departing in the austral summer. However, while the same areas were used by individuals in different years, they were not necessarily used at the same times during the non-breeding period. Conclusions: Even in tropical systems with huge ranges of migratory routes and timings, our results suggest benefits of consistency in individual migratory behaviours. Identifying the factors that drive and maintain between-individual variation in migratory behaviour, and the consequences for breeding success and survival, will be key to understanding the consequences of environmental change across migratory ranges

An “orientation sphere” visualization for examining animal head movements

Animal behavior is elicited, in part, in response to external conditions, but understanding how animals perceive the environment and make the decisions that bring about these behavioral responses is challenging. Animal heads often move during specific behaviors and, additionally, typically have sensory systems (notably vision, smell, and hearing) sampling in defined arcs (normally to the front of their heads). As such, head‐mounted electronic sensors consisting of accelerometers and magnetometers, which can be used to determine the movement and directionality of animal heads (where head “movement” is defined here as changes in heading [azimuth] and/or pitch [elevation angle]), can potentially provide information both on behaviors in general and also clarify which parts of the environment the animals might be prioritizing (“environmental framing”). We propose a new approach to visualize the data of such head‐mounted tags that combines the instantaneous outputs of head heading and pitch in a single intuitive spherical plot. This sphere has magnetic heading denoted by “longitude” position and head pitch by “latitude” on this “orientation sphere” (O‐sphere). We construct the O‐sphere for the head rotations of a number of vertebrates with contrasting body shape and ecology (oryx, sheep, tortoises, and turtles), illustrating various behaviors, including foraging, walking, and environmental scanning. We also propose correcting head orientations for body orientations to highlight specific heading‐independent head rotation, and propose the derivation of O‐sphere‐metrics, such as angular speed across the sphere. This should help identify the functions of various head behaviors. Visualizations of the O‐sphere provide an intuitive representation of animal behavior manifest via head orientation and rotation. This has ramifications for quantifying and understanding behaviors ranging from navigation through vigilance to feeding and, when used in tandem with body movement, should provide an important link between perception of the environment and response to it in free‐ranging animals.Deanship of Scientific Research at the King Saud University through Vice Deanship of Research Chairs; The National Geographic Global Exploration Fund. Grant Number: #GEFNE89‐13; European Research Council under the European Union's Horizon 2020 research and innovation program Grant. Grant Number: 715874; Royal Society/Wolfson Lab refurbishment scheme; Royal Society. Grant Number: 2009/R3 JP090604; Natural Environment Research Council. Grant Numbers: NE/I002030/1, NE/R001669/1; King Abdullah University of Science and Technology. Grant Number: CAASE.http://www.ecolevol.orghj2020Mammal Research InstituteZoology and Entomolog

Is adolescent body mass index and waist circumference associated with the food environments surrounding schools and homes? A longitudinal analysis

Background: There has been considerable interest in the role of access to unhealthy food options as a determinant of weight status. There is conflict across the literature as to the existence of such an association, partly due to the dominance of cross-sectional study designs and inconsistent definitions of the food environment. The aim of our study is to use longitudinal data to examine if features of the food environment are associated to measures of adolescent weight status. Methods: Data were collected from secondary schools in Leeds (UK) and included measurements at school years 7 (ages 11/12), 9 (13/14), and 11 (15/16). Outcome variables, for weight status, were standardised body mass index and standardised waist circumference. Explanatory variables included the number of fast food outlets, supermarkets and ‘other retail outlets’ located within a 1 km radius of an individual’s home or school, and estimated travel route between these locations (with a 500 m buffer). Multi-level models were fit to analyse the association (adjusted for confounders) between the explanatory and outcome variables. We also examined changes in our outcome variables between each time period. Results: We found few associations between the food environment and measures of adolescent weight status. Where significant associations were detected, they mainly demonstrated a positive association between the number of amenities and weight status (although effect sizes were small). Examining changes in weight status between time periods produced mainly non-significant or inconsistent associations. Conclusions: Our study found little consistent evidence of an association between features of the food environment and adolescent weight status. It suggests that policy efforts focusing on the food environment may have a limited effect at tackling the high prevalence of obesity if not supported by additional strategies

Impacts of herbivory by ecological replacements on an island ecosystem

The use of ecological replacements (analogue species to replace extinct taxa) to restore ecosystem functioning is a promising conservation tool. However, this approach is controversial, in part due to a paucity of data on interactions between analogue species and established taxa in the ecosystem. We conducted ecological surveys, comprehensively DNA barcoded an ecosystem's flora and inferred the diet of the introduced Aldabra giant tortoise, acting as an ecological replacement, to understand how it might have modified island plant communities on a Mauritian islet. Through further dietary analyses, we investigated consequential effects on the threatened endemic Telfair's skink. Dietary overlap between tortoises and skinks was greater than expected by chance. However, there was a negative correlation between tortoise and skink preferences in herbivory and minimal overlap in the plants most frequently consumed by the reptiles. Changes in the plant community associated with 7 years of tortoise grazing were characterised by a decrease in the percentage cover of native herbs and creepers, and an increase in the cover of an invasive herb when compared to areas without tortoises. However, tortoise dietary preferences themselves did not directly drive changes in the plant community. Tortoises successfully dispersed the seeds of an endemic palm, which in time may increase the extent of unique palm-rich habitat. We found no evidence that tortoises have increased the extent of plant species hypothesised to be part of a lost Mauritian tortoise grazed community. Synthesis and applications. Due to a negative correlation in tortoise and skink dietary preferences and minimal overlap in the most frequently consumed taxa, the presence of tortoises is unlikely to have detrimental impacts on Telfair's skinks. Tortoise presence is likely to be beneficial to skinks in the long term by increasing the extent of palm-rich habitat. Although tortoises are likely to play a role in controlling invasive plants, they are not a panacea for this challenge. After 7 years, tortoises have not resurrected a lost tortoise grazed community that we hypothesise might have existed in limited areas on the islet, indicating that further interventions may be required to restore this plant community