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.     

Movement of two grassland butterflies in the same habitat network: the role of adult resources and size of the study area

Abstract. 1.  Movement patterns of two butterfly species (meadow brown Maniola jurtina L. and scarce copper Lycaenae virgaureae L.) were studied in a 172 ha area within a landscape with a high percentage of suitable habitats for mark–release–recapture experiments.
2.  Adult resource density, but not patch size or larval food plant abundance, influenced the numbers and the fractions of residents, emigrants, and immigrants.
3.  Differences between species were observed in movement frequency and maximum distances moved but not in mean distances moved.
4.  The scarce copper showed much greater movement ability than expected from the results of published studies. This is believed to be a result of the comparatively large size of the study area and the high cover of suitable habitat (>50%).
5.  The mean and maximum distances travelled by butterflies reflected differences in the size of the study area.     

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.     

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.     

Contrasting movement patterns in two species of chequerspot butterflies, Euphydryas aurinia and Melitaea phoebe, in the same patch network

Abstract.  1. Mark–release–recapture studies were conducted on two species of chequerspot butterfly, Euphydryas aurinia and Melitaea phoebe , in the same habitat patch network in Yanjiaping, a small basin in the Taihang Mountains, north-west of Beijing, China, in 2000.
2. Euphydryas aurinia tended to stay in the habitat patches and to move to neighbouring patches, whereas M. phoebe moved widely among patches in the entire network.
3. The parameters of the virtual migration model showed higher daily emigration propensity in M. phoebe and in E. aurinia males than in E. aurinia females, and significantly greater average daily movement distance in M. phoebe than in E. aurinia .
4. The results are consistent with the previous findings showing genetic structuring among local populations of E. aurinia but not among local populations of M. phoebe .
5. Based on the genetic and ecological results, it was concluded that E. aurinia has a classic metapopulation in the study area, whereas M. phoebe appears to have a source–sink metapopulation.
6. In 2000, when there was an overall increase in the abundance of the two species, the limited mobility of E. aurinia resulted in an increase in the average local population size, whereas the increase in the number of local populations in M. phoebe was due to its high mobility .     

An experimental examination of the effects of habitat quality on the dispersal and local abundance of the butterfly Parnassius smintheus

Abstract 1. Nectar flower abundance was manipulated through flower removal, and sex ratio was manipulated by moving individual butterflies within a series of nine alpine meadows. The movement and abundance of the butterfly Parnassius smintheus in the meadows were monitored using mark–release–recapture methods.
2. A total of 937 butterflies, 698 males and 239 females, was captured. There were 223 observed between-meadow movements. Fifty-two per cent of males and 35% of females moved among meadows.
3. The immigration of male butterflies was related positively to nectar flowers, host plant abundance, and female butterflies. Male emigration was not affected by any of the treatments. The number of males captured was related positively to nectar flowers and host plants but not affected by sex ratio. The number of resident male butterflies was greater in meadows containing flowers and was related positively to host plant abundance, but unaffected by sex ratio.
4. Flower removal, sex ratio, and abundance of Sedum had no significant effect on the abundance, movement, or residence time for female butterflies, in part due to small sample size.
5. The fact that males immigrate to higher quality meadows suggests that male butterflies are assessing meadow quality, either by sampling meadows or potentially from a distance using olfactory cues.     

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.     

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.     

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.     

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.     

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.     

A Bayesian estimate of harbour seal survival using sparse photo-identification data

Survival rates have rarely been estimated for pinniped populations due to the constraints of obtaining unbiased sample data. In this paper, we present an approach for estimating survival probabilities from individual recognition data in the form of photographic documentation of pelage patterns. This method was applied to estimate adult (age 2+) survival for harbour seals in the Moray Firth, NE Scotland. An astronomical telescope was used to obtain digital images of individual seals, and high-quality images were used to document the annual presence or absence of individuals at a single haul-out site over a 4-year period. A total of 95 females, 10 males and 57 individuals of unknown sex were photographically documented during the study period. Survival and recapture probabilities were estimated using Jolly–Seber mark–recapture models in a Bayesian statistical framework. Computer-intensive Markov Chain Monte Carlo methods were used to estimate the probability distributions for the survival and recapture probabilities, conveying the full extent of the uncertainty resulting from unavoidably sparse observational data. The deviance information criterion was used to identify a best-fitting model that accounted for variation in the probability of capture between sexes, with constant survival. The model estimated adult survival as 0.98 (95% probability interval of 0.94–1.00) using our photo-identification data alone, and 0.97 (0.92–0.99) with the use of an informative prior distribution based on previously published estimates of harbour seal survival. This paper represents the first survival estimate for harbour seals in the UK, and the first survival estimate using photo-identification data in any species of pinniped.     

Movement patterns of Rhyssomatus lineaticollis Say (Coleoptera: Curculionidae) within and among Asclepias syriaca (Asclepiadaceae) patches in a fragmented landscape

Abstract.  1. Dispersal capabilities of organisms are critical in determining the landscape population structure of species as well as their likelihood of survival in fragmented landscapes. Using mark–recapture techniques on the monophagous weevil Rhyssomatus lineaticollis Say (Curculionidae), within- and between-patch dispersal capabilities, landscape level population structure, and the role of beetle density and host patch characteristics in setting distances, amounts, and timing of dispersal were studied.
2. The data indicate that R. lineaticollis is sedentary, with 50% of recaptured beetles moving < 1 m and the maximum distance moved < 1 km. Within- and between-patch movement of beetles was unrelated to host plant patch characteristics and beetle densities.
3. Despite limited dispersal, R. lineaticollis probably functions as a patchy population in east-central Iowa, U.S.A. because dispersals between patches are common and because all host patches surveyed contained this herbivore, indicating a lack of suitable vacant patches, a prerequisite for metapopulation structure.
4. Between-patch distances are well within the dispersal capabilities of R. lineaticollis , although this may be the result of an increase in the density of patches of its host, Asclepias syriaca , in the landscape over the last 150 years as a result of human disturbance and this species' weedy habit.
5. Metapopulation structure in monophagous prairie herbivores may be most likely in species whose non-weedy host plants form highly predictable resources in space and time, but which are now widely scattered in habitat fragments.     

Comparative study on the consequences of culling badgers (Meles meles) on biometrics, population dynamics and movement

1.  Capture–mark–recapture data were used to describe the process of recovery from a typical badger removal operation (BRO) at North Nibley, Gloucestershire, UK, which was carried out as part of the government's strategy to control bovine tuberculosis. Data on biometrics, demographics and movement from this low-density disturbed population were compared with those of two nearby high-density undisturbed populations (Wytham Woods and Woodchester Park, UK) in order to study fundamental principles of population dynamics and density-dependence.
2.  Badgers moved more between social groups at North Nibley than in the other study areas, particularly in the immediate aftermath of the removal operation.
3.  Recolonization of the vacated habitat occurred in the first instance by young females.
4.  Although in the first year after the BRO no cubs had been reared in any of the culled groups, and although the shortage of sexually mature boars may have limited the reproductive output of sows in the following year, the population took only 3 years to recover to its (already lowered) preremoval density.
5.  Losses from the adult (and cub) population due to mortality or emigration were smaller at North Nibley than at the other sites.
6.  There was much evidence that during 1995 and 1996 density-dependent effects constrained the reproductive output of the high-density populations, and some support for the hypothesis that badgers exhibit the non-linear 'large mammal' type of functional response to density.
7.  Badgers at North Nibley were younger, heavier and in better condition than badgers at Wytham Woods and Woodchester Park.
8.  We argue that the disease dynamics are likely to be different in disturbed compared with undisturbed badger populations, and that this could affect the effectiveness of BROs.     

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.     

Seasonal dynamics, movements and the effects of experimentally increased female densities on a population of imaginal Calopteryx aequabilis (Odonata: Calopterygidae)

Abstract. 1. A population of Calopteryx aequabilis Say was sampled daily on a tributary of Canard River, Kings County, Nova Scotia, for the entire flight season in 1983 (29 May to 13 August), using capture–mark–recapture techniques.
2. 2701 sightings of 678 individuals were obtained along a 635 m segment of the stream. A maximum daily count of 174 imagines was reached on 11 June, after which the population gradually declined.
3. More females than males were marked but sexually mature males outnumbered females at the water on all but four days.
4. Immigration rather than local emergence accounted for a large proportion of the population after 20 June.
5. Females were consistently vagile; males were site–specific but occasionally moved long distances between captures.
6. Males and females first marked as tenerals became reproductively mature after about 5 days.
7. We experimentally increased female density on a partially isolated section of the study stream to see how increased female numbers affected the demographics and movement patterns of the population.
8. Residence times for introduced and resident females were similar. In contrast, during a similar introduction of males a year earlier, most introduced males disappeared quickly.
9. Males decreased the distance they travelled daily between captures, their total distance travelled and their range following the introduction, and females showed a tendency (not statistically significant) toward increased movements and dispersal, as predicted.     

Migration and Allee effects in the six-spot burnet moth Zygaena filipendulae

Abstract 1. Migration into local populations may increase the likelihood of persistence but emigration may decrease the persistence of small and isolated populations. The dispersal behaviour of a day-flying moth Zygaena filipendulae was examined to determine whether emigration is correlated positively or negatively with population size and host plant density.
2. A mark–release–recapture study showed that most moths moved small distances (< 40 m on average) and only 6% of movements were > 100 m.
3. Twenty-five individuals moved between populations, a measured exchange rate of 8%. Moths were more likely to move between patches that were close together and they moved to relatively large patches.
4. The fraction of residents increased with increasing population size in the patch and increasing host plant cover. Relatively high proportions of individuals left small patches with small moth populations.
5. Moths released in grassland lacking Lotus corniculatus (the host plant) tended to leave the area and biased their movement towards host plant areas, whereas those released within an area containing L. corniculatus tended to stay in that area.
6. Biased movement away from small populations and areas of low host plant density (normally with low population density) was found. This migration-mediated Allee effect is likely to decrease patch occupancy in metapopulations, the opposite of the rescue effect. The effects on metapopulation persistence are not known.     

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.     

Habitat-based statistical models for predicting the spatial distribution of butterflies and day-flying moths in a fragmented landscape

1.  Most species' surveys and biodiversity inventories are limited by time and money. Therefore, it would be extremely useful to develop predictive models of animal distributions based on habitat, and to use these models to estimate species' densities and range sizes in poorly sampled regions.
2.  In this study, two sets of data were collected. The first set consisted of over 2000 butterfly transect counts, which were used to determine the relative density of each species in 16 major habitat types in a 35-km² area of fragmented landscape in north-west Wales. For the second set of data, the area was divided into 140 cells using a 500-m grid, and the extent of each habitat and the presence or absence of each butterfly and moth species was determined for each cell.
3.  Logistic regression was used to model the relationship between species' distribution and predicted density, based on habitat extent, in each grid square. The resultant models were used to predict butterfly distributions and occupancy at a range of spatial scales.
4.  Using a jack-knife procedure, our models successfully reclassified the presence or absence of species in a high percentage of grid squares (mean 83% agreement). There were highly significant relationships between the modelled probability of species occurring at regional and local scales and the number of grid squares occupied at those scales.
5.  We conclude that basic habitat data can be used to predict insect distributions and relative densities reasonably well within a fragmented landscape. It remains to be seen how accurate these predictions will be over a wider area.     

Regional dynamics of a patchily distributed herbivore along an altitudinal gradient

Abstract.  1. Metapopulation dynamics should be more important at the borders of species distributions due to two main factors: (1) populations are less abundant and fluctuate more at the borders than in the centre of their distributions, and (2) resources in the range margins of species distributions are often more scarce and fragmented.
2. Most metapopulation studies have been performed in a fraction of the entire distribution of species. The main goal here is to study the population dynamics of a narrowly distributed species including both the borders and the centre of the distribution, and to test the predictions described above.
3. The density and extinction events in a patchily distributed species, Timarcha lugens , was quantified for 5 years along an altitudinal gradient including the upper and lower limits of the species distribution. The dispersal ability of Timarcha was also studied using a mark–release–recapture study.
4. Extinction events and empty patches were only found at the borders of Timarcha distribution. The fluctuation in beetle density was greater in patches suffering extinction events. Resource abundance was negatively related to beetle density and positively related to extinction events. In addition, the dispersal rate among patches was very low and beetles moved distances of no further than 25 m.
5. Population density governs the extinction events in this system, and its fluctuation was more evident near the border of the distribution. Both factors together with the relative population stability in patches at medium and high altitudes, and the low dispersal rate of the individuals support the idea of a source–sink metapopulation structure in T. lugens .