Mark–recapture estimates of recruitment, survivorship and population growth rate for the screwworm fly, Cochliomyia hominivorax

Abstract.  Pradel model mark–release–recapture estimates of survivorship, φ , recruitment, f , and the rate of density-independent population growth, λ , are presented for eight mark–recapture studies of the screwworm Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae) from Costa Rica, totalling 19 573 released and 4476 recaptured flies. Corroborative estimates of survivorship and the rate of population growth based on an extensive review of the literature are also reported. Weighted-mean ± standard error of the mean (SEM) mark–release–recapture estimates of survivorship, recruitment and the rate of population growth were φ   =  0.798 ± 0.008, f   = 0.193 ± 0.008 and λ  = 1.005 ± 0.002, respectively. Population doubling time was estimated from λ at 139 days. Estimates of φ and λ from the literature both exceeded those calculated by mark–recapture methods and estimates of population doubling times were consequently shorter.     

Male-biased dispersal in a tropical Australian snake (Stegonotus cucullatus, Colubridae)

Sex-based differences in dispersal distances can affect critical population parameters such as inbreeding rates and the spatial scale of local adaptation. Males tend to disperse further than females in mammals, whereas the reverse is true for birds; too few reptiles have been studied to reveal generalities for that group. Although reptiles are most diverse and abundant in the tropics, few tropical reptiles have been studied in this respect. We combine data from a long-term (10-year) mark–recapture study with genetic information (based on nine microsatellite markers) on slatey-grey snakes ( Stegonotus cucullatus , Colubridae) in the Australian wet-dry tropics. Males attain larger body sizes than females, and both genetic and mark–recapture data show that males also disperse further than females. Recapture records show that hatchling males dispersed away from their release points whereas hatchling females did not, and adult males moved further than adult females. In the genetic analysis, males contributed less to overall F _ST and relatedness than did females ( F _STm = 0.0025, F _STf = 0.0275, P  < 0.001; r _m = 0.0053; r _f = 0.0550; P  < 0.001). Spatial autocorrelation analyses within the largest population revealed a similar pattern, with spatial structuring stronger for females than males. Overall, our genetic analyses not only supported the mark–recapture data, but also extended our insights by revealing occasional long-distance dispersal not detected by the mark–recapture study.     

Intercalibration of hydroacoustic and mark–recapture methods for assessing the spawning population size of a threatened fish species

Hydroacoustic counting and a three-year mark–recapture study with passive integrated transponders (PIT tags) were used to estimate the size of a spawning population of nase Chondrostoma nasus , a threatened potamodromous cyprinid that undertakes annual spawning migrations into a tributary of the Danube River. In 2005, the estimates of the size of the spawning population from the hydroacoustic counts ( N = 2234, 95% CL 1929–2538) and from the Jolly–Seber model ( N = 1198, 95% CL 461–5842) corresponded well. Estimates from the jackknife-estimator based on the hydroacoustic counts yielded slightly higher values ( N = 2783, 95% CL 2529–3037), but were still in the same order of magnitude as those from the hydroacoustic and mark–recapture approach. At low run-size, hydroacoustic counting was more time consuming and technically demanding than mark–recapture studies. At the same time, it was non-invasive, provided real-time data on a fine temporal scale, and estimates showed less variability than the Jolly–Seber model. Mark–recapture of fish in spawning streams involved substantial disturbance at a sensitive stage of the life cycle. Hence, hydroacoustics is highly suited for population estimates of threatened potamodromous fishes, where interference needs to be minimized.     

Estimating abundance for a savanna elephant population using mark–resight methods: a case study for the Tembe Elephant Park, South Africa

Elephants living in dense woodlands are difficult to count. Many elephant populations in Africa occur in such conditions. Estimates of these populations based on total counts, aerial counts and dung counts often lack information on precision and accuracy. We use standard mark–recapture field methods to obtain estimates of population size with associated confidence limits. We apply this approach to a closed elephant population in the Tembe Elephant Park (300 km²), South Africa. A registration count completed in 4 months gives a known population size. We evaluate mark–recapture models against the known population size. Individual identification profiles obtained for elephants during the registration count and mark–recapture events indicate that at least 167 elephants live in the park. We consider this value as an estimate of the minimum number alive. We include 189 sightings of bulls and 37 sightings of breeding herds in the mark–recapture modelling. Of the models we test (Petersen, Schnabel, Schumacher, Jolly–Seber, Bowden's, Poisson and negative binomial), Bowden's gives an estimate closest to the registration count. Assumptions of the model are not violated. For all models except one (negative binomial), our estimates improve with increased sampling intensity. Confidence intervals do not improve with increased effort except for the Schnabel model. Mark–recapture methods should be considered as reliable estimators of population size for elephants occurring in dense woodlands and forests when other methods cannot be relied on.     

Estimating the population size of specialised solitary bees

Abstract.  1. Reliable methods for quantifying population size are crucial for strategies to conserve endangered wild-bee species. Estimates of population size obtained through survey walks were compared with estimates obtained through mark–recapture studies in 10 populations of the red-listed solitary bee Andrena hattorfiana in southern Sweden.
2. The mean number of bees observed during survey walks was strongly correlated with estimates of population size obtained with mark–recapture. It was found that 5.5–23.4% (mean 13.4%) of the total population was observed during an average survey walk.
3. One component in mark–recapture analysis is the measure of survival of individuals. In the largest bee population, females of A. hattorfiana that emerged in early season were found to forage for pollen on average 18.4 days.
4. The findings suggest that during large-scale surveys, for example re-inventories for red-listed species, the population size of solitary bees can be quantified reliably and effectively by performing survey walks in a two-step process. The first step consists of survey walks to establish the relationship between number of bee observations per survey walk and mark–recapture population size for a small set of populations. In the second, simple observation survey walks can be performed for a large set of populations. In each population of A. hattorfiana , it is recommended that at least six survey walks are performed.     

Sex biases in dispersal and philopatry: insights from a meta-analysis based on capture–mark–recapture studies of damselflies

Sex-biased dispersal is well known for birds and mammals, typically by females and males, respectively. Little is known about general patterns of sex-biased dispersal in other animal taxa. We reviewed return rates for a model group of invertebrates (damselflies) and explored putative costs and benefits of dispersal by males and females. We used published capture–mark–recapture data and examined whether a sex bias existed in likelihood of recapture at least once, at both emergence and/or breeding sites. We assessed whether this metric of likelihood of recapture was indicative of dispersal or philopatry, and whether any emerging pattern(s) were consistent across damselfly families. Using a meta-analysis, we found a higher likelihood of recapture at least once for males than for females at both natal sites and breeding sites, which seemed attributable to higher female-biased dispersal, although female-biased mortality cannot be discounted particularly for some species. Sex biases in dispersal among damselflies may be understood based on sex differences in maturation rate and foraging behaviour, both of which should affect the costs and benefits of dispersing. This hypothesis may be useful for explaining patterns of dispersal in other animal taxa.     

Comparison of social networks derived from ecological data: implications for inferring infectious disease dynamics

1.  Social network analyses tend to focus on human interactions. However, there is a burgeoning interest in applying graph theory to ecological data from animal populations. Here we show how radio-tracking and capture–mark–recapture data collated from wild rodent populations can be used to generate contact networks.
2.  Both radio-tracking and capture–mark–recapture were undertaken simultaneously. Contact networks were derived and the following statistics estimated: mean-contact rate, edge distribution, connectance and centrality.
3.  Capture–mark–recapture networks produced more informative and complete networks when the rodent density was high and radio-tracking produced more informative networks when the density was low. Different data collection methods provide more data when certain ecological characteristics of the population prevail.
4.  Both sets of data produced networks with comparable edge (contact) distributions that were best described by a negative binomial distribution. Connectance and closeness were statistically different between the two data sets. Only betweenness was comparable. The differences between the networks have important consequences for the transmission of infectious diseases. Care should be taken when extrapolating social networks to transmission networks for inferring disease dynamics.     

Modelling mortality and dispersal: consequences of parameter generalisation on metapopulation dynamics

Modelling dispersal is a fundamental step in the design of population viability analyses. Here, we address the question of the generalisation of population viability analysis models across landscapes by comparing dispersal between two metapopulations of the bog fritillary butterfly ( Proclossiana eunomia ) living in similar highly fragmented landscapes (<1% of suitable habitat in 9 km²). Differences in dispersal patterns were investigated using the virtual migration (VM) model, which was parameterised with capture–mark–recapture data collected during several years in both landscapes. The VM model allows the estimation of 6 parameters describing dispersal and mortality as well as the simulation of dispersal in the landscapes. The model revealed large differences in the VM parameter estimates between the two landscapes and consequently, simulations indicated differential rates of emigration and dispersal mortality. Furthermore, results from crossed-simulations i.e. simulations performed in one of the landscape but using parameter estimates from the other landscape emphasize that dispersal parameters are very specific to each metapopulation and to their landscape. Hence, we urge conservation biologists to be cautious with such parameter generalisations, even for the same species in comparable landscapes.     

The influence of spatial scale on quantifying insect dispersal: an analysis of butterfly data

Abstract. 1. A linear relationship between mean movement distances recorded and the size of the study area was found in a comparison of five mark–release–recapture studies of the meadow brown butterfly.
2. The scale impact on mean butterfly movement distances was also apparent when comparing the results for different butterfly species reported in 21 mark–release–recapture studies.     

Form,function and consequences of density dependence in a long‐distance migratory bird

The density dependence of demographic parameters and its implications for population regulation have long been recognized. Recent work has revealed potential effects of density on mating systems and sexual selection, but few studies concurrently assess the consequences of density on both demography and sexual selection. Such an approach is important because population processes and individual behaviors can interact to influence population growth and evolutionary trajectories. In this study, we tested the density dependence of breeding success, extra‐pair paternity, and the opportunity for sexual selection in a population of American redstarts Setophaga ruticilla using two different measures of density. To evaluate temporal patterns, we analyzed annual territory density, based on the total number of territories at our study site each year. To evaluate spatial patterns, we analyzed local territory density within years, based on the number of territories surrounding a focal territory. Greater annual density was associated with fewer offspring fledged per female, a reduced mean population rate of fledging success, and a lower relative contribution of extra‐pair paternity to male fitness. Greater local density was associated with fewer offspring fledged, reduced fledgling success, higher rates of nest loss, and higher rates of paternity loss on focal territories. Interestingly, greater local density was also associated with greater nestling mass on focal territories, which could imply that more densely‐packed territories contain superior resources. Overall, our results suggest that the effects of crowding via greater territory density reduce fecundity through increased nest predation, rather than reduced food availability, and increase rates of extra‐pair paternity. Thus, the selective pressures faced by individuals and their reproductive behaviors are likely to differ based on the annual and local density they experience, which may then feed back into population demography.     

Testing assumptions of mark–recapture protocols for estimating population size using Australian mound-building, subterranean termites

1. Forager population size of two species of mound-building, subterranean termite ( Coptotermes lacteus , Rhinotermitidae and Nasutitermes exitiosus , Termitidae) was estimated using three mark–recapture protocols. These estimates varied widely within and between colonies (≈ 0.3–200 million for C. lacteus and 0.2–3 million for N. exitiosus ). The variation in the estimates is explained in part by violation of the assumptions of the protocols.
2. The fat-stain markers, although persistent in the laboratory, faded rapidly in the field, and were transferable from marked individuals to unmarked individuals by cannibalism.
3. Marked individuals did not mix randomly or evenly with unmarked foraging individuals in space or time, as marked individuals were recaptured in widely varying numbers at different feeding sites sampled simultaneously. Importantly, foragers displayed feeding site fidelity and avoided disturbed feeding sites.
4. The likelihood of recapture differed between castes and instars; there was a higher recapture rate of large workers and soldiers relative to smaller workers.
5. The mark–recapture protocols provided inaccurate and unreliable forager population estimates, up to two orders of magnitude larger than direct counts of entire mound colonies. Thus the weighted mean estimates from more complex triple-mark–recapture protocols were not necessarily better than Lincoln index estimates from simpler single-mark–recapture protocols.
6. Mark–recapture studies may provide useful information about forager behaviour and foraging territories.     

Impact of an exceptional winter flood on the population dynamics of bearded tits (Panurus biarmicus)

Mark–recapture data are used to investigate the impact of an exceptional winter flood on the population dynamics of an isolated bearded tit Panurus biarmicus population in north-west England. Adult numbers increased threefold (from 60 to 180 individuals) between 1992 and 2000, but declined by 94% during 2000/2001. This large reduction in numbers was caused by severe over-winter mortality associated with a prolonged flood of the Phragmites litter layer, the main winter foraging habitat of bearded tits, followed immediately by cold weather. At the end of the flood, bearded tits were 20% lighter than during previous winters. Population changes in other years were accurately predicted by annual variation in recruitment, and there was evidence that recruitment was higher following the introduction of artificial nest boxes and was density dependent. This study highlights the potential threat to bearded tits in Europe of predicted increases in the frequency and extent of winter flooding, and the potential utility of measures like artificial nest boxes that aim to promote recruitment. Recent extensions of methodology now permit a detailed exploration of animal population dynamics from mark–recapture data alone.     

Interactive effects of distance and matrix on the movements of a peatland dragonfly

We conducted a mark–release–recapture survey of a peatland dragonfly ( Leucorrhinia hudsonica ) in each of two years (2002; 2003) in a harvested forest landscape in western Newfoundland, Canada. The odds of an individual male moving between peatlands was influenced by both the distance between peatlands and the type of intervening habitat (the matrix). Specifically, at meso scales (>700  m) there was a positive effect of the amount of cut matrix between peatlands on the odds of moving, but at fine scales (<700  m) there was the opposite effect; proportionally fewer individuals moved between peatlands. The odds of moving out of a peatland decreased as the surface area of water in the peatland increased. Multi-state mark–recapture models showed that the daily probability of a male moving between any two peatlands was 1.9% in 2002 and 6.9% in 2003 (n=1527 and 1280 marked individuals). The results suggest that additional empirical studies that directly measure patterns of movement with respect to landscape structure at multiple spatial scales in other taxa and situations are needed in order to uncover other possible non-linear changes in behavior.     

Stochastic density dependence in population size of a benthic clonal invertebrate: the regulating role of fission

The influence of environmental variation on the demography of clonal organisms has been poorly studied. I utilise a matrix model of the population dynamics of the intertidal zoanthid Palythoa caesia to examine how density dependence and temporal variation in demographic rates interact in regulating population size. The model produces realistic simulations of population size, with erratic fluctuations between soft lower and upper boundaries of approximately 55 and 90% cover. Cover never exceeds the maximum possible of 100%, and the population never goes to extinction. A sensitivity analysis indicates that the model’s behaviour is driven by density dependence in the fission of large colonies to produce intermediate sized colonies. Importantly, there is no density-dependent mortality in the model, and density dependence in recruitment, while present, is unimportant. Thus it appears that the main demographic processes which are considered to regulate population size in aclonal organisms may not be important for clonal species. Received: 18 August 1999 / Accepted: 29 October 1999     

Predation of a cave fish (Poecilia mexicana, Poeciliidae) by a giant water-bug (Belostoma, Belostomatidae) in a Mexican sulphur cave

Abstract.  1. Caves are often assumed to be predator-free environments for cave fishes. This has been proposed to be a potential benefit of colonising these otherwise harsh environments. In order to test this hypothesis, the predator–prey interaction of a belostomatid (predator) and a cave fish (prey) occurring in the Cueva del Azufre (Tabasco, Mexico) was investigated with two separate experiments.
2. In one experiment, individual Belostoma were given a chance to prey on a cave fish, the cave form of the Atlantic molly ( Poecilia mexicana ), to estimate feeding rates and size-specific prey preferences of the predator. In the other experiment, population density of Belostoma was estimated using a mark–recapture analysis in one of the cave chambers.
3. Belostomatids were found to heavily prey on cave mollies and to exhibit a prey preference for large fish. The mark–recapture analysis revealed a high population density of the heteropterans in the cave.
4. The absence of predators in caves is not a general habitat feature for cave fishes. None the less predation regimes differ strikingly between epigean and hypogean habitats. The prey preference of Belostoma indicates that cave-dwelling P. mexicana experience size-specific predation pressure comparable with surface populations, which may have implications for life-history evolution in this cave fish.     

Survival-variation within and between functional categories of the African multimammate rat

1. By identifying ecological factors specific to functional categories of individuals, it may be possible to understand the mechanisms underlying life-history evolution and population dynamics. While empirical analyses within the field of population biology have focused on changes in population size, theoretical models assuming differential sensitivities of population growth rate or fitness to demographic parameters have mostly been untested, particularly against data on small mammals.
2. Statistical modelling of capture–mark–recapture data on the multimammate rat ( Mastomys natalensis ) from Tanzania shows that: (i) females survive slightly better than males and subadults survive much better than adults; (ii) temporal variation of survival of all individuals is similarly related to the rainfall of the month; (iii) subadults exhibit a strongly density-dependent low persistence rate in the population immediately after their first capture; (iv) subadults survival in later months is, however, positively related to density; and (v) adult survival shows negative density-dependence.
3. Both density-dependent and density-independent factors simultaneously determine stage-dependent survival variation of the multimammate rat. Whereas environmental factors in this population seem to affect survival rates of all individuals in a similar manner, density-dependent relationships are more complex.
4. The patterns of survival variation in small mammals may be different from those observed in large mammals.
5. Further studies of demography in small mammals should aim at understanding how much of the variability in population growth rate is accounted for by the variability of the demographic rates resulting from limiting (density-independent) and regulating (density-dependent) factors, respectively. This study emphasizes the use of robust and accurate statistical methods as well as stage- or age-structured population modelling.     

An approach for assessing paddlefish Polyodon spathula (Walbaum, 1792) populations using mark‐recapture information

Historically, management of fish populations has been achieved through the use of age‐derived estimates of growth and mortality. For long‐lived species such as the paddlefish, Polyodon spathula, the validation of calcified structures is necessary to correct for the presence of false annuli or the absence of growth rings. Regardless, numerous studies on paddlefish populations throughout their range have continued the use of un‐validated age estimates to evaluate dynamic rate functions. The use of mark‐recapture studies has been applied widely to evaluate growth of short‐lived fishes, but only recently to a few long‐lived freshwater fishes (i.e. white sturgeon, shovelnose sturgeon, and pallid sturgeon). This study provides the first simultaneous evaluation of both mark‐recapture and age‐estimate information in determining population characteristics for paddlefish. In doing so, this study has determined that the P. spathula population in the Black River below Clearwater Dam, Missouri is sustainable. Additionally, mark‐recapture information is sufficient to produce accurate and reliable assessments of paddlefish populations in lieu of validated aging structures; future management should be centered on accurate scientific methods, which is not the case when using un‐validated aging structures (e.g. scales, otoliths, fin rays, dentary bones) to determine population parameters. Mark‐recapture information can provide an accurate, alternative source of growth and mortality information for use in evaluating and managing paddlefish populations throughout their range.     

Three ways of assessing metapopulation structure in the butterfly Plebejus argus

1. Three independent methods were used to investigate population structure in the butterfly Plebejus argus . First, migration and dispersal ability were measured by mark–release–recapture in seven adjacent habitat patches, and by release of butterflies in unoccupied habitat. Secondly, colonization of newly created habitat was observed over 7 years. Finally, genetic differentiation of local populations within a metapopulation was investigated. Sampled local populations included parts of the mark–release–recapture study area.
2. Plebejus argus is relatively sedentary: the maximum movement detected was 395 m, and only 2% of individuals moved further than 100 m between recaptures on different days. None the less, adjacent local populations in the mark–release–recapture study area were linked by occasional migration, with ≈ 1.4% of individuals moving between patches separated by 13–200 m.
3. Despite low mobility, observed colonizations occurred rapidly over distances of 1 km. Because P. argus occurs at high population densities, 1.4% migration can generate enough migrants to colonize newly suitable habitat quickly at this spatial scale.
4. Mark–release–recapture data were used to predict that there would be limited genetic differentiation through drift between local populations at this spatial scale. The prediction was supported by allele frequency data for the same local populations.
5. Genetic differentiation often indicates higher levels of migration than are revealed by the movements of marked individuals. This study shows that when experimental releases and extensive marking are undertaken in areas that are large relative to most movements, indirect measures of gene flow and direct measures of dispersal can concur.
6. Evidence from the three different approaches was complementary, indicating that P. argus occurs as metapopulations within the study area.     

Double-Observer Line Transect Methods: Levels of Independence

Summary .  Double-observer line transect methods are becoming increasingly widespread, especially for the estimation of marine mammal abundance from aerial and shipboard surveys when detection of animals on the line is uncertain. The resulting data supplement conventional distance sampling data with two-sample mark–recapture data. Like conventional mark–recapture data, these have inherent problems for estimating abundance in the presence of heterogeneity. Unlike conventional mark–recapture methods, line transect methods use knowledge of the distribution of a covariate, which affects detection probability (namely, distance from the transect line) in inference. This knowledge can be used to diagnose unmodeled heterogeneity in the mark–recapture component of the data. By modeling the covariance in detection probabilities with distance, we show how the estimation problem can be formulated in terms of different levels of independence. At one extreme, full independence is assumed, as in the Petersen estimator (which does not use distance data); at the other extreme, independence only occurs in the limit as detection probability tends to one. Between the two extremes, there is a range of models, including those currently in common use, which have intermediate levels of independence. We show how this framework can be used to provide more reliable analysis of double-observer line transect data. We test the methods by simulation, and by analysis of a dataset for which true abundance is known. We illustrate the approach through analysis of minke whale sightings data from the North Sea and adjacent waters.     

Incorporating Genotype Uncertainty into Mark–Recapture-Type Models For Estimating Abundance Using DNA Samples

Summary .  Sampling DNA noninvasively has advantages for identifying animals for uses such as mark–recapture modeling that require unique identification of animals in samples. Although it is possible to generate large amounts of data from noninvasive sources of DNA, a challenge is overcoming genotyping errors that can lead to incorrect identification of individuals. A major source of error is allelic dropout, which is failure of DNA amplification at one or more loci. This has the effect of heterozygous individuals being scored as homozygotes at those loci as only one allele is detected. If errors go undetected and the genotypes are naively used in mark–recapture models, significant overestimates of population size can occur. To avoid this it is common to reject low-quality samples but this may lead to the elimination of large amounts of data. It is preferable to retain these low-quality samples as they still contain usable information in the form of partial genotypes. Rather than trying to minimize error or discarding error-prone samples we model dropout in our analysis. We describe a method based on data augmentation that allows us to model data from samples that include uncertain genotypes. Application is illustrated using data from the European badger ( Meles meles ).