Point-count methods to monitor butterfly populations when traditional methods fail: a case study with Miami blue butterfly (original) (raw)
Related papers
Butterfly monitoring methods: the ideal and the real world
Israel Journal of Ecology …, 2008
Butterflies may serve as indicators of biodiversity trends, but for this purpose reliable methods of monitoring their distribution and abundance are essential. We discuss advantages and disadvantages of the currently used methods and suggest potential refinements, based on methodological advances achieved in other organisms. While assessing butterfly distribution, it is vital to account for imperfect species detection at investigated sites. This can be achieved through conducting repeated presence-absence surveys within a single season, and analyzing data with statistical models that estimate detection probability and site occupancy by a species. Transect counts, predominantly used for assessing butterfly abundance in monitoring programs, are cost-effective and easy to implement, but less reliable than mark-release-recapture sampling frequently applied for the same purpose in research studies. Deficiencies of transect counts stem from the fact that they do not account for individual detection probability and temporal fragmentation of butterfly populations, i.e., the situation in which just a small fraction of individuals belonging to a single generation is present on any day of a season. Consequently, transect counts can only yield relative abundance indices, which presumably correlate well with daily butterfly numbers, but not necessarily with their seasonal population sizes. Possible refinements to transect counts that would allow the estimation of individual detection probability include double observer or double zone approaches. In contrast, finding an effective way to estimate longevity (a measure of temporal fragmentation) with transect counts seems impossible. Instead, efforts should be made to evaluate how variation in longevity affects transect-count results.
Monitoring Butterfly Abundance: Beyond Pollard Walks
2012
Most butterfly monitoring protocols rely on counts along transects (Pollard walks) to generate species abundance indices and track population trends. It is still too often ignored that a population count results from two processes: the biological process (true abundance) and the statistical process (our ability to properly quantify abundance). Because individual detectability tends to vary in space (e.g., among sites) and time (e.g., among years), it remains unclear whether index counts truly reflect population sizes and trends. This study compares capture-mark-recapture (absolute abundance) and countindex (relative abundance) monitoring methods in three species (Maculinea nausithous and Iolana iolas: Lycaenidae; Minois dryas: Satyridae) in contrasted habitat types. We demonstrate that intraspecific variability in individual detectability under standard monitoring conditions is probably the rule rather than the exception, which questions the reliability of countbased indices to estimate and compare specific population abundance. Our results suggest that the accuracy of countbased methods depends heavily on the ecology and behavior of the target species, as well as on the type of habitat in which surveys take place. Monitoring programs designed to assess the abundance and trends in butterfly populations should incorporate a measure of detectability. We discuss the relative advantages and inconveniences of current monitoring methods and analytical approaches with respect to the characteristics of the species under scrutiny and resources availability.
Distance sampling and the challenge of monitoring butterfly populations
Methods in Ecology and Evolution, 2011
Isaac, Nick J.B.; Cruickshanks, Katie L.; Weddle, Ann M.; Rowcliffe, J. Marcus; Brereton, Tom M.; Dennis, Roger L.H.; Shuker, David M.; Thomas, Chris D.. 2011 Distance sampling and the challenge of monitoring butterfly populations. Methods in Ecology and Evolution, 2 (6). The NERC and CEH trade marks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. Distance sampling and the challenge of monitoring butterfly 1 populations 2 3 Nick J.Summary 1 1. Abundance indices generated by the UK Butterfly Monitoring Scheme (UKBMS) have 2 been influential in informing our understanding of environmental change and highlighting 3 UK conservation priorities. Here we critically evaluate the standard 'Pollard Walk' 4 methodology employed by the UKBMS. 5
Characterizing urban butterfly populations: the case for purposive point-count surveys
Urban Ecosystems
Developing effective butterfly monitoring strategies is key to understanding how butterflies interact with urban environments, and, in turn, to developing local conservation practices. We investigated two urban habitat types (public gardens and restored/reconstructed prairies) and compared three survey methods (Pollard transects, purposive point counts, and random point counts) to determine which was most productive for detecting butterflies and assessing family diversity. We conducted 66 butterfly surveys by using each method (198 total) from May through September in 2015 and 2016 at six sites (three public gardens and three prairies) in Ames, Ankeny and Des Moines, Iowa. All survey methods were used on 11 sampling dates at each site. Overall, we observed 2,227 butterflies representing 38 species: 1,076 in public gardens and 1,151 in prairie areas. We used a smaller data set standardized for survey effort, including 1,361 of these sightings, to compare survey methods and habitat types. Although there were no significant differences in number of butterfly sightings between the two habitats, more sightings (798) were documented by using purposive point counts when compared to Pollard transects (297) or random point counts (266) (for both comparisons, p < 0.0001). Occupancy modeling also indicated that purposive point counts were most effective in detecting certain species of butterflies, most notably those within the Pieridae (whites, sulphurs) and Papilionidae (swallowtails). We conclude that public gardens and restored/reconstructed prairies in urban settings can provide important butterfly habitat, and that purposive point-count surveys are most effective for detecting butterflies in these relatively small-scale landscape features.
Standardized butterfly surveys: comparing transect counts and area-time counts in insect monitoring
Biodiversity and Conservation
The observed insect decline, which threatens agricultural productivity and ecosystem stability, calls for comprehensive international insect monitoring. Monitoring implementation demands standardisation and the integration of new and innovative methods. Therefore, we compared two quantitative butterfly survey methods – the commonly applied transect counts (or ‘Pollard walks’) and more extensive area-time counts. We evaluated the influence of the two methods on the estimation of biodiversity variables such as species richness and species abundance to examine whether they could be applied alternatively for the calculation of butterfly trend indicators. During 576 surveys we conducted 5-minute transect counts and 25-minute area-time counts simultaneously at 144 different sites in Western Austria. The estimated relative butterfly abundance of the two methods for 119 observed species showed a strong linear relationship. While we found 2.4 times more species per site with the more extensi...
Reduced-effort schemes for monitoring butterfly populations
Journal of Applied Ecology, 2007
1Butterflies are one of the few insect groups that can be monitored effectively and have the potential to develop national and Europe-wide trends in abundance.2For 20 widespread butterfly species, we assess the relative efficiency of reduced-effort schemes compared to the existing design and estimate the number of sites required to detect changes of given magnitudes over specified periods of time.3A scheme restricted to three counts during July and August requires twice as many monitored sites on average to achieve comparable precision to the existing 26-week scheme in the United Kingdom. Such a scheme requires 430 monitoring sites on average to achieve 80% power (5% significance level) for detecting a 25% decline in abundance over 10 years.4Such a reduced-effort scheme may also mean that volunteers are more willing to record in areas where they are likely to see only a few individuals of a few common species (such as on intensively farmed areas). This could potentially help to ensure that butterfly monitoring schemes achieve a more even geographical coverage and less of a bias towards areas rich in butterflies.5Synthesis and applications. Schemes with few sampling visits per year are cost-effective for expanding butterfly monitoring across Europe, and can be applied to national monitoring programmes and lead to effective assessment of continent-wide trends in populations.Butterflies are one of the few insect groups that can be monitored effectively and have the potential to develop national and Europe-wide trends in abundance.For 20 widespread butterfly species, we assess the relative efficiency of reduced-effort schemes compared to the existing design and estimate the number of sites required to detect changes of given magnitudes over specified periods of time.A scheme restricted to three counts during July and August requires twice as many monitored sites on average to achieve comparable precision to the existing 26-week scheme in the United Kingdom. Such a scheme requires 430 monitoring sites on average to achieve 80% power (5% significance level) for detecting a 25% decline in abundance over 10 years.Such a reduced-effort scheme may also mean that volunteers are more willing to record in areas where they are likely to see only a few individuals of a few common species (such as on intensively farmed areas). This could potentially help to ensure that butterfly monitoring schemes achieve a more even geographical coverage and less of a bias towards areas rich in butterflies.Synthesis and applications. Schemes with few sampling visits per year are cost-effective for expanding butterfly monitoring across Europe, and can be applied to national monitoring programmes and lead to effective assessment of continent-wide trends in populations.
Comparison of trends in butterfly populations between monitoring schemes
Journal of Insect Conservation, 2014
Butterflies are an important indicator of the impacts of environmental change. Butterfly monitoring schemes (BMS) have provided national and Europe-wide trends in their abundance and been widely used for research. Most schemes sample sites that are self-selected by contributors and therefore tend to cover locations that are rich in butterflies. To provide a more representative assessment of butterfly populations, the wider countryside butterfly survey (WCBS) was developed with a stratifiedrandom sample of survey sites across the UK. We compare butterfly trends from the WCBS locations against those measured from traditional butterfly transects which are typically located in areas of good quality semi-natural habitats. Across the 26 species analysed, there was a significant positive relationship between trends measured from the two schemes between 2009 and 2013, the period when both schemes were operating fully. There was a tendency (17 out of 26 species analysed) for these changes to be greater within WCBS compared to traditional BMS transects, although this effect was not consistent across comparisons between pairs of consecutive years. When assessing these individual year-to-year changes, there was however a significant correlation between the two schemes in all cases. Over relatively short time periods, weather patterns are likely to dominate butterfly population fluctuations and lead to comparable trends across monitoring schemes. Over longer time periods, differences in land management may affect habitat condition differently for protected areas versus the wider countryside and it is therefore important to maintain comprehensive butterfly monitoring programmes to detect and interpret such effects.
The Canadian Entomologist, 2012
Assessing biodiversity is essential in conservation biology but the resources needed are often limited. Citizen science, by which volunteers gather data at low cost, represents a potential solution for the lack of resources if it produces usable data for scientific means. Scientific inventories for butterflies are often performed with a Pollard transect, a standardised surveying technique that generates high-quality data. General microhabitat surveys (GMSs) are potentially more appealing to amateurs participating in citizen science projects because they are less constrained. We compare estimates of butterfly species richness acquired by Pollard transects to those obtained by GMSs. We demonstrate that GMSs allow surveyors to detect more butterfly species and a more complete portrait of local butterfly assemblages for the same number of individuals captured.
Estimation of the occupancy of butterflies in diverse biogeographic regions
Diversity and Distributions, 2016
Aim We explored the extent to which occupancy of butterflies within three biogeographic regions could be explained by vegetation structure and composition, topography and other environmental attributes; whether results were consistent among regions; and whether assumptions of closure were met with assemblage-level sampling designs. Location Chesapeake Bay Lowlands (Virginia), central Great Basin (Nevada) and western Great Basin (Nevada and California) (all USA). Methods We applied single-season occupancy models that either assumed closure or relaxed the closure assumption to data from 2013 and 2014 for 13-15 species in each region. Results Maximum single-year estimates of detection probabilities ranged from 0.14 to 0.99, and single-year occupancy from 0.28 to 0.98. The assumption of closure was met for a maximum of 54% of the species in a given region and year. Detection probabilities of > 90% of the species in each region increased as the categorical abundance of nectar or mud increased. Measures of the dominance or abundance of deciduous woody species and structural heterogeneity were included in the greatest number of occupancy models for the Chesapeake Bay Lowlands, which may in part reflect the intensity of browsing by whitetailed deer (Odocoileus virginianus). Elevation and precipitation were prominent covariates in occupancy models for Great Basin butterflies. Main conclusions Because occupancy models do not rely on captures or observations of multiple individuals in a population, they potentially can be applied to a relatively high proportion of the species in an assemblage. However, estimation of occupancy is complicated by taxonomic, temporal and spatial variation in phenology. In multiple, widely divergent ecosystems, all or some associations between covariates and detection probability or occupancy for at least one-third of the species could not be estimated, often because a given species rarely was detected at locations with relatively low or high values of a covariate. Despite their advantages, occupancy models may leave unexplained the environmental associations with the distributions of many species.