Census Size Research Articles

Sexual selection has minimal impact on effective population sizes in species with high rates of random offspring mortality: An empirical demonstration using fitness distributions.

The effective population size (N(e)) is a fundamental parameter in population genetics that influences the rate of loss of genetic diversity. Sexual selection has the potential to reduce N(e) by causing the sex-specific distributions of individuals that successfully reproduce to diverge. To empirically estimate the effect of sexual selection on N(e), we obtained fitness distributions for males and females from an outbred, laboratory-adapted population of Drosophila melanogaster. We observed strong sexual selection in this population (the variance in male reproductive success was ∼14 times higher than that for females), but found that sexual selection had only a modest effect on N(e), which was 75% of the census size. This occurs because the substantial random offspring mortality in this population diminishes the effects of sexual selection on N(e), a result that necessarily applies to other high fecundity species. The inclusion of this random offspring mortality creates a scaling effect that reduces the variance/mean ratios for male and female reproductive success and causes them to converge. Our results demonstrate that measuring reproductive success without considering offspring mortality can underestimate Ne and overestimate the genetic consequences of sexual selection. Similarly, comparing genetic diversity among different genomic components may fail to detect strong sexual selection.

Effects of genetic drift in a small population of Atlantic cod (Gadus morhua kildinensis Derjugin) landlocked in a meromictic lake: genetic variation and conservation measures

Landlocked populations of normally salt-water, bottom-dwelling Atlantic cod exist in a few circumpolar meromictic lakes. One such population, the Kildin cod, inhabits Mogilnoe Lake (Kildin Island, the Barents Sea) that is listed among regional nature reserves. The lake has three main strata of water of about 5 m each: an upper level with nearly fresh water, a saline layer, and an anaerobic zone at the bottom. The fish lives in the saline stratum and appears in the fresh layer as well. Available food is poor, the adults heavily prey on cod juveniles. The Kildin cod has distinct morphological features, faster growth rate, earlier age of maturation, and shorter longevity that likely developed in response to the unusual lake environment. Genetic and capture-mark-recapture data show that the Kildin cod greatly differs from its marine counterparts: It has an effective population size of about one hundred and an average adult census size of about half a thousand, reproductively isolated from a parental marine population around 1800 years ago, lost a large portion of microsatellite and mitochondrial DNA variation due to long-term genetic drift, but still maintains variation at allozyme loci. DNA markers of the Kildin cod do not carry novel mutations, but their multilocus genotypes seem to be unique to the lake population. The suggested conservation strategy includes: (1) the lake and its drainage area should be strongly protected from any detrimental human activities; (2) the transplantation of any genetic material into the cod population of Mogilnoe Lake should be strongly prohibited.

Weed Suppression Success Can Depend on Removal Pattern and Gene Dispersal Distance: Modeling Callery Pear

Substantial resources are spent each year on weed control, but in many cases eradication projects are incomplete. Here we used the computer program NEWGARDEN to model whether alternate geometric patterns of incomplete removal (99% removed) of the increasingly invasive Callery pear from an isolated fragment differentially affect the rate of population recovery and genetic diversity retention. Geometric patterns of remaining founders within the fragment (1% of the fragment area) included: (A) a long rectangular strip centered on one edge; (B) a square at one corner; (C) a central square; or (D) scattered randomly throughout the entire fragment. Population re-growth and genetic diversity retention measures for each geometric removal pattern were modeled under two contrasting gene dispersal patterns (via both offspring and pollen): short versus long dispersal (both leptokurtic relative to the pistillate plant). After 14 bouts of mating, the greatest difference in census size among comparative recovery populations amounted to 393% (centered founders, long gene dispersal > scattered founders, short gene dispersal). The best pattern of removal for suppressing population regrowth was to leave founders scattered throughout the fragment when gene dispersal was short, or at one corner if gene dispersal was long. The only removal pattern that differed substantially in population genetics characteristics was when remnant individuals were left scattered throughout the fragment and dispersal was short (alleles continued to be lost; observed heterozygosity dropped 13.3% and was still rapidly declining; and inbreeding and/or subdivision were moderate (Fit= 0.12) and still rapidly increasing). Such comparative modeling can be used to suggest removal patterns that might greatly outperform other removal modalities in terms of suppressing the return of weed populations. The effectiveness of such modeling will be improved by acquisition of accurate life history information of targeted species.

Population genetic data pertinent to the conservation of Bulgarian chamois (Rupicapra rupicapra balcanica)

In Bulgaria, chamois (Rupicapra rupicapra balcanica) are protected by law and it has been recommended to assess their genetic diversity, level of inbreeding, and extent of introgression by Alpine chamois (R. r. rupicapra) that were released in the last century in the Rhodope Mountains. Chamois (n = 81) collected between 2009 and 2013 at the “Izvora State Hunting Reserve” (ISHR, western Rhodopes, a major source for chamois translocations in Bulgaria; census size: 200–250) were screened for allelic variability at 12 microsatellite loci and compared to chamois (R. r. rupicapra, n = 135) from six populations in the Austrian Alps. Indices of genetic variability were significantly lower for the ISHR population than for the Austrian populations. A significant bottleneck signal was observed for the ISHR population, but no distinct inbreeding signal due to non-random mating. F-statistics, absolute genetic distances, Bayesian STRUCTURE and assignment analyses, and a factorial correspondence analysis concordantly indicated distinct differentiation between the ISHR and Austrian chamois. STRUCTURE identified some few ISHR chamois as possibly introgressed by Alpine chamois. ONeSAMP revealed effective population size estimates of Ne ≈ 50 for the ISHR population. A reduction of shooting quotas, a reinforcement of poaching control, and exchanging chamois with other Bulgarian populations should increase its Ne to prevent further loss of genetic variability. Screening for introgression should be extended to other Bulgarian populations, particularly to areas where Alpine chamois were released in the past; and it should accompany all translocations, to prevent possible dissemination of introgressed chamois.

Population size is weakly related to quantitative genetic variation and trait differentiation in a stream fish.

How population size influences quantitative genetic variation and differentiation among natural, fragmented populations remains unresolved. Small, isolated populations might occupy poor quality habitats and lose genetic variation more rapidly due to genetic drift than large populations. Genetic drift might furthermore overcome selection as population size decreases. Collectively, this might result in directional changes in additive genetic variation (VA ) and trait differentiation (QST ) from small to large population size. Alternatively, small populations might exhibit larger variation in VA and QST if habitat fragmentation increases variability in habitat types. We explored these alternatives by investigating VA and QST using nine fragmented populations of brook trout varying 50-fold in census size N (179-8416) and 10-fold in effective number of breeders, Nb (18-135). Across 15 traits, no evidence was found for consistent differences in VA and QST with population size and almost no evidence for increased variability of VA or QST estimates at small population size. This suggests that (i) small populations of some species may retain adaptive potential according to commonly adopted quantitative genetic measures and (ii) populations of varying sizes experience a variety of environmental conditions in nature, however extremely large studies are likely required before any firm conclusions can be made.

Accurate Non-parametric Estimation of Recent Effective Population Size from Segments of Identity by Descent

Existing methods for estimating historical effective population size from genetic data have been unable to accurately estimate effective population size during the most recent past. We present a non-parametric method for accurately estimating recent effective population size by using inferred long segments of identity by descent (IBD). We found that inferred segments of IBD contain information about effective population size from around 4 generations to around 50 generations ago for SNP array data and to over 200 generations ago for sequence data. In human populations that we examined, the estimates of effective size were approximately one-third of the census size. We estimate the effective population size of European-ancestry individuals in the UK four generations ago to be eight million and the effective population size of Finland four generations ago to be 0.7 million. Our method is implemented in the open-source IBDNe software package.

Assessment of census (N) and effective population size (N e ) reveals consistency of N e single-sample estimators and a high N e /N ratio in an urban and isolated population of fire salamanders

Amphibians are the most threatened vertebrates on Earth, and one of the main factors involved in their decline is the loss and fragmentation of their natural habitats. Contemporary urban development is a major cause of habitat fragmentation, and populations trapped within urban environments offer a unique opportunity to study effects of fragmentation. Here, we compared, for the first time in fire salamanders (Salamandra salamandra), estimates of census (N) and effective population size (N e ) in a small urban population in the city of Oviedo (Spain). We performed a 4 year capture-mark-recapture study and used three single-sample N e estimators based on 58 individuals genotyped for 15 polymorphic microsatellite loci. Our study showed a small ( $$\hat{N} = 113$$ salamanders; 95 % CI 100–142) but dense population (mean 0.45 individuals per m2), while single-sample estimators provided congruent N e estimates. A high N e /N population size ratio (range 0.50–0.84) obtained in this small and isolated population suggests the existence of mechanisms of genetic compensation (low reproductive variance and multiple paternity) in fire salamanders.

Institutional Variation in Traumatic Brain Injury Acute Rehabilitation Practice

ObjectiveTo describe institutional variation in traumatic brain injury (TBI) inpatient rehabilitation program characteristics and evaluate to what extent patient factors and center effects explain how TBI inpatient rehabilitation services are delivered. DesignSecondary analysis of a prospective, multicenter, cohort database. SettingTBI inpatient rehabilitation programs. ParticipantsPatients with complicated mild, moderate, or severe TBI (N=2130). InterventionsNot applicable. Main Outcome MeasuresMean minutes; number of treatment activities; use of groups in occupational therapy, physical therapy, speech therapy, therapeutic recreation, and psychology inpatient rehabilitation sessions; and weekly hours of treatment. ResultsA wide variation was observed between the 10 TBI programs, including census size, referral flow, payer mix, number of dedicated beds, clinician experience, and patient characteristics. At the centers with the longest weekday therapy sessions, the average session durations were 41.5 to 52.2 minutes. At centers with the shortest weekday sessions, the average session durations were approximately 30 minutes. The centers with the highest mean total weekday hours of occupational, physical, and speech therapies delivered twice as much therapy as the lowest center. Ordinary least-squares regression modeling found that center effects explained substantially more variance than patient factors for duration of therapy sessions, number of activities administered per session, use of group therapy, and amount of psychological services provided. ConclusionsThis study provides preliminary evidence that there is significant institutional variation in rehabilitation practice and that center effects play a stronger role than patient factors in determining how TBI inpatient rehabilitation is delivered.

The relationship between abundance and genetic effective population size in elasmobranchs: an example from the globally threatened zebra shark Stegostoma fasciatum within its protected range

Genetic effective population size (Ne) estimators are useful as applied conservation tools. Many elasmobranch (shark and ray) species are threatened at local and global scales, and tools to monitor these populations are greatly needed. This study investigates contemporary Ne and its relationship with census size (Nc) in a population of zebra sharks (Stegostoma fasciatum). Our Ne using the linkage disequilibrium method, 377 (95 % CI 274–584) was found to closely approximate the mark-recapture Nc for this population of mature sharks (458, 95 % CI 298–618), with an Ne/Nc ratio of 0.82 (SE = 0.33). Furthermore, we conducted a series of sensitivity analyses to examine how the numbers of samples and loci affect the precision and accuracy of the estimators. We demonstrate that for this species robust and precise estimates are obtainable with a minimum of 91 samples (approximately 20 % of the census population) and 10 microsatellite loci. These findings contribute important information to the greater body of Ne and Ne/Nc relationships in elasmobranchs and wildlife populations as well as provide important guidelines for implementing genetic monitoring in elasmobranch conservation efforts.

Census and effective population sizes of white‐spotted charr (Salvelinus leucomaenis) in a fragmented landscape

AbstractSeveral habitat models have been proposed to predict population size for stream fishes and to guide habitat assessment and monitoring techniques. However, most models do not incorporate the potential advantage of molecular genetic markers. We conducted a field survey and microsatellite DNA analyses to quantify the relationships among genetic diversity, census/effective population size and habitat variables in fragmented populations of white‐spotted charr (Salvelinus leucomaenis). The census population size significantly increased with the stream length, the number of pools and a pool‐riffle sequence index, a proxy for channel‐unit habitat type complexity within reaches. Population density was correlated with the pool‐riffle sequence index only. Genetic diversity and effective population size were not correlated with the habitat variables or census population size. There was a lack of isolation‐by‐distance population structure in the studied populations. Our results suggest that stream length and the number of pools within reaches associated with habitat complexity are the habitat variables that explain the majority of variation in population size of white‐spotted charr. Our findings provide further evidence that census population size per se is a poor indicator of the inclusive genetic diversity within populations in a fragmented landscape.

EFFECTIVE SIZE OF AUTO-TETRAPLOID POPULATION UNDER PARTIAL SELFING

Effective population size is defined as the number of breeding individual in an idealized population that would show the same amount of dispersion of allele frequencies under random genetic drift or the same amount of inbreeding as the population under consideration. Effective population size depends on the census size of the population and the mating system. In autotetraploid population, effective population size also depends on the probability of double reduction, i.e., a meiotic event when two sister chromatids end in the same gamete. In this research, we will study the effect of the probability of double reduction on the effective size of autotetraploid population reproduced by partial selfing. The formula for the effective population size was derived by equating the variance of the change in gene frequency in idealized population and its value in the autotetraploid population with arbitrary rate of partial selfing and double reduction. The resulted formula, and numerical study based on the formula, indicated that the effective size decreases by the increase of probability of double reduction and the rate of selfing. When there is complete selfing, however, the effective size is not affected by the probability of double reduction.

Temporal genetic and demographic monitoring of pond-breeding amphibians in three contrasting population systems

Quantifying the relationship between demographic patterns and genetic diversity are important in predicting temporal population genetic changes. To make predictions there must be an understanding of the relationship between census size, the effective number of breeders (Nb) and effective population size (Ne). We evaluate the temporal genetic variation between three populations of Ambystoma salamanders, and compare genetic and demographic estimates of Nb and Ne. We sampled two wetlands, RB and GB for A. opacum and sampled A. talpoideum at RB, over a 20-year period. Ambystoma opacum colonized the RB wetland in 1980 and the population has steadily expanded as A. talpoideum has declined towards local extinction; the GB population of A. opacum has remained relatively large and stable over this same time period. Genetic variation at 10 microsatellites remained stable at each population over the sampled time frame, and did not reflect changes in population size. Genetic estimates of Nb also did not reflect demographic trends, and were lower than demographic estimates of Nb. Genetic methods of determining Ne gave similar estimates to demographic methods. Our findings indicate that sample sizes and number of markers typically used in genetic studies do not provide enough precision to monitor population size changes in amphibians, which likely violate many of the assumptions of Nb and Ne estimation models. These findings should be considered when using Ne in conservation and management assessments of amphibian populations.

Morphological and genomic comparisons of Hawaiian and Japanese Black-footed Albatrosses (Phoebastria nigripes) using double digest RADseq: implications for conservation.

Evaluating the genetic and demographic independence of populations of threatened species is important for determining appropriate conservation measures, but different technologies can yield different conclusions. Despite multiple studies, the taxonomic status and extent of gene flow between the main breeding populations of Black-footed Albatross (Phoebastria nigripes), a Near-Threatened philopatric seabird, are still controversial. Here, we employ double digest RADseq to quantify the extent of genomewide divergence and gene flow in this species. Our genomewide data set of 9760 loci containing 3455 single nucleotide polymorphisms yielded estimates of genetic diversity and gene flow that were generally robust across seven different filtering and sampling protocols and suggest a low level of genomic variation (θ per site = ∼0.00002–0.00028), with estimates of effective population size (Ne = ∼500–15 881) falling far below current census size. Genetic differentiation was small but detectable between Japan and Hawaii (FST ≈ 0.038–0.049), with no FST outliers. Additionally, using museum specimens, we found that effect sizes of morphological differences by sex or population rarely exceeded 4%. These patterns suggest that the Hawaiian and Japanese populations exhibit small but significant differences and should be considered separate management units, although the evolutionary and adaptive consequences of this differentiation remain to be identified.

Broad-scale genetic patterns of New Zealand abalone, Haliotis iris, across a distribution spanning 13° latitude and major oceanic water masses.

The New Zealand black-foot abalone, Haliotis iris, or pāua, is endemic to the rocky reefs surrounding New Zealand, whose main land mass spans 13° of latitude and separates the Tasman Sea from the Pacific Ocean. In this study, we examined the population genetic structure of this important commercial, cultural and recreational species by genotyping nine microsatellite loci in 485 pāua from 27 locations distributed across mainland New Zealand and the Chatham Islands. We found low, but significant, levels of genetic differentiation. Key genetic breaks were identified among the Chatham Islands and mainland samples; patterns that are strongly corroborated by prior work employing mtDNA sequences. AMOVAs indicated that samples from the south of the North Island were more similar to the South Island samples than to other North Island samples, however multivariate analysis and Bayesian clustering could not identify a significant pattern. Differentiation between the Chatham Islands and the mainland is most likely due to isolation by distance, while differentiation of North Island samples corresponds with major components of New Zealand's oceanography, Cook Strait and the East Cape. Despite intense fishing pressure, we detected no signature of genetic bottlenecks in any region suggesting that population sizes have remained relatively stable over recent time or that the census size of this species is much larger than its effective population size.

Estimating effective population size of guanacos in Patagonia: an integrative approach for wildlife conservation

By the mid-1900s the guanaco (Lama guanicoe) approached extinction in southern South America due to habitat destruction and hunting. In order to maintain the ecological prominence of this iconic species, as well as assist in the management of populations that are emerging economically while increasing in conservation value, accurate and potentially rapid estimates of effective population size (Ne) (demographic and/or genetic) are essential. Estimates of Ne generally focus on the genetic effective population size; however, we posited that both parameters may be necessary to provide more accurate and timely estimates. Therefore, we examined the performance of three demographic and four genetic estimators of Ne of guanacos in Torres del Paine National Park, Chile, at different years and time intervals between 1987 and 1997. We compared our estimates with census estimates of the adult population size (Nac) during the same time period. Average Ne/Nac ratios of demographic estimates varied between 0.04 and 0.99 of the adult census size. Genetic estimates varied between 0.02 and 0.08 of the adult census size. Based upon group composition and population size (n = 82) of guanacos in 1975, the number of breeding adults was 44 animals. Mean Ne of the single-sample and temporal genetic estimators was 43.1, and 34.3, respectively; estimated Ne of one of the demographic estimators was 41. Our findings suggest that intermittent genetic estimates of Ne (via fecal samples, carcasses, blood collection during capture, and/or other non-invasive methods) can provide crucial information regarding the genetic integrity of increasingly isolated populations of wild South American camelids. Considering the overall performance of these estimators, and differences in how each functions, we recommend an integrative approach using both genetic and demographic estimators, to evaluate Ne for the wild South American camelids and other species with polygynous mating systems.

Population structure and effective/census population size ratio in threatened three-spined stickleback populations from an isolated river basin in northwest Spain.

Variability at 20 microsatellite loci was examined to assess the population genetic structure, gene flow, and effective population size (N(e)) in three populations of three-spined stickleback (Gasterosteus aculeatus) from the upper basin of the Miño River in Galicia, NW Spain, where this species is threatened. The three populations showed similar levels of genetic diversity. There is a significant genetic differentiation between the three populations, but also significant gene flow. N(e) estimates based on linkage disequilibrium yielded values of 355 for the Miño River population and 241 and 311 for the Rato and Guisande Rivers, respectively, although we expect that these are overestimates. N(e) estimates based on temporal methods, considering gene flow or not, for the tributaries yielded values of 30-56 and 47-56 for the Rato and Guisande Rivers, respectively. Estimated census size (N(c)) for the Rato River was 880 individuals. This yielded a N(e)/N(c) estimate of 3-6 % for temporal estimation of N(e), which is within the empirical range observed in freshwater fishes. We suggest that the three populations analyzed have a sufficient level of genetic diversity with some genetic structure. Additionally, the absence of physical barriers suggests that conservation efforts and monitoring should focus in the whole basin as a unit.

Conservation genetics and genetic mating system of the yellow-shouldered blackbird (Agelaius xanthomus), an endangered island endemic

The yellow-shouldered blackbird (Agelaius xanthomus) is a managed endemic species in Puerto Rico that experienced a bottleneck in the 1970s and currently faces high levels of brood parasitism and habitat loss. Little is known about its overall genetic profile and genetic mating system, which potentially shapes effective population size by contributing to variation in reproductive success. Here I used nine microsatellite loci to characterize the population genetics and mating system of a southwestern Puerto Rican population. Although the population showed no evidence of inbreeding, it had significantly lower allelic diversity, effective population size, and expected heterozygosity than both island and continental populations of the related red-winged blackbird (A. phoeniceus). In particular, the low effective population size of the yellow-shouldered blackbird (~71, 18 % of the 2012 census size) raises concerns about its long-term viability. Paternity tests on 30 nests provided the first evidence of genetic polyandry in this species. Of all young, 23 % were extra-pair (sired by a male other than the social father), and 37 % of nests contained extra-pair young, which does not differ from proportions observed in red-winged blackbirds. Extra-pair paternity was not found to contribute significantly to variation in individual reproductive output, suggesting the bottleneck is more likely to have contributed to the current population genetic profile than the species’ mating system. Together, these data suggest that while genetic diversity on the individual level may be intact, the population as a whole remains vulnerable to adverse stochastic events and loss of evolutionary potential.

Similar plastic responses to elevated temperature among different-sized brook trout populations.

The potential influence of population size on the magnitude of phenotypic plasticity, a key factor in adaptation to environmental change, has rarely been studied. Conventionally, small populations might exhibit consistently lower plasticity than large populations if small population habitats are generally poor in quality and if genetic diversity underpinning plasticity is lost as population size is reduced. Alternatively, small populations might exhibit (1) consistently higher plasticity as a response to the increased environmental variation that can accompany habitat fragment size reduction or (2) greater variability in plasticity, as fragmentation can increase variability in habitat types. We explored these alternatives by investigating plasticity to increasing temperature in a common garden experiment using eight fragmented populations of brook trout varying nearly 50-fold in census size (179-8416) and 10-fold in effective number of breeders (18-135). Across six early-life-history traits and three temperatures, we found almost no evidence for differences in either the magnitude or variability of plasticity in relation to population size, despite that one temperature represented an extreme climate warming scenario. The documentation of similar plastic responses of small and large populations suggests that phenotypic plasticity is not reduced as population size decreases, and that even very small populations of some species might have the ability to respond to climate change.

Population differentiation determined from putative neutral and divergent adaptive genetic markers in Eulachon (Thaleichthys pacificus, Osmeridae), an anadromous Pacific smelt.

Twelve eulachon (Thaleichthys pacificus, Osmeridae) populations ranging from Cook Inlet, Alaska and along the west coast of North America to the Columbia River were examined by restriction-site-associated DNA (RAD) sequencing to elucidate patterns of neutral and adaptive variation in this high geneflow species. A total of 4104 single-nucleotide polymorphisms (SNPs) were discovered across the genome, with 193 putatively adaptive SNPs as determined by F(ST) outlier tests. Estimates of population structure in eulachon with the putatively adaptive SNPs were similar, but provided greater resolution of stocks compared with a putatively neutral panel of 3911 SNPs or previous estimates with 14 microsatellites. A cline of increasing measures of genetic diversity from south to north was found in the adaptive panel, but not in the neutral markers (SNPs or microsatellites). This may indicate divergent selective pressures in differing freshwater and marine environments between regional eulachon populations and that these adaptive diversity patterns not seen with neutral markers could be a consideration when determining genetic boundaries for conservation purposes. Estimates of effective population size (N(e)) were similar with the neutral SNP panel and microsatellites and may be utilized to monitor population status for eulachon where census sizes are difficult to obtain. Greater differentiation with the panel of putatively adaptive SNPs provided higher individual assignment accuracy compared to the neutral panel or microsatellites for stock identification purposes. This study presents the first SNPs that have been developed for eulachon, and analyses with these markers highlighted the importance of integrating genome-wide neutral and adaptive genetic variation for the applications of conservation and management.

Post‐fragmentation population structure in a cooperative breeding Afrotropical cloud forest bird: emergence of a source‐sink population network

The impact of demographic parameters on the genetic population structure and viability of organisms is a long-standing issue in the study of fragmented populations. Demographic and genetic tools are now readily available to estimate census and effective population sizes and migration and gene flow rates with increasing precision. Here we analysed the demography and genetic population structure over a recent 15-year time span in five remnant populations of Cabanis's greenbul (Phyllastrephus cabanisi), a cooperative breeding bird in a severely fragmented cloud forest habitat. Contrary to our expectation, genetic admixture and effective population sizes slightly increased, rather than decreased between our two sampling periods. In spite of small effective population sizes in tiny forest remnants, none of the populations showed evidence of a recent population bottleneck. Approximate Bayesian modelling, however, suggested that differentiation of the populations coincided at least partially with an episode of habitat fragmentation. The ratio of meta-Ne to meta-Nc was relatively low for birds, which is expected for cooperative breeding species, while Ne /Nc ratios strongly varied among local populations. While the overall trend of increasing population sizes and genetic admixture may suggest that Cabanis's greenbuls increasingly cope with fragmentation, the time period over which these trends were documented is rather short relative to the average longevity of tropical species. Furthermore, the critically low Nc in the small forest remnants keep the species prone to demographic and environmental stochasticity, and it remains open if, and to what extent, its cooperative breeding behaviour helps to buffer such effects.