Calculation of collated indices of abundance of butterflies based on monitored sites

Abstract.

• 1 The Butterfly Monitoring Scheme uses regular transect counts on fixed sites to establish annual indices of abundance of butterfly species in the United Kingdom. The annual change in collated index for each species has hitherto been calculated as a simple ratio between total counts summed over all participating sites.
• 2 A revised method for calculation of collated indices is proposed, which applies a logarithmic transformation to site values so as to downweight the influence on the index of the sites with greatest numbers of a species. Zero counts are handled comparably with non-zero values. An alternative method using geometric mean ratios is also examined.
• 3 Indices calculated using the logarithmic transformation are compared with those calculated using the traditional method. Two internal tests of dependency of collated indices on the sites with highest abundance are made. Another evaluation uses regression analysis for the effects of temperature and rainfall on collated indices of butterfly abundance.
• 4 The first internal test shows that logarithmic transformation reduces the dependence of the collated index on the sites of highest abundance for twenty-five out of twenty-seven species examined; while a second test shows a reduction for twenty-six out of forty-two species, and an increase for one species. The number of significant regressions on temperature variables increases with the use of the logarithmic transformation from 11% to 13% of tests made, and on rainfall from 10% to 11%.
• 5 The geometric mean ratio method introduces considerable biases in its treatment of zero values, for which a remedy is not available.
• 6 Although the revised collated indices calculated using logarithmic transformation are broadly comparable with traditionally calculated values, the reductions in dependency on sites with the most abundant populations render the revised indices less subject to perturbation due to local ‘noise’, and so more suitable for research on factors influencing butterfly abundance.

     

Evaluation of community indices in seasonal assemblages of butterflies (Lepidoptera) at different frequency of transect count

Community indices were evaluated at different frequency of transect counts of butterflies by randomization. Randomized samples were obtained by re-arranging 1, 3, 6, 12 and 18 counts from 18 counts at a study site (Hiraoka), and 1, 2, 3, 5 and 15 from 15 at another site (Narukawa), in 1994. Morisita's new estimate of species richness, QM gave a good estimate when the number of counts was five or more. QM estimated from the sum of both assemblages (58 species) was 70.7, while 73 species were recorded at least once from 1990 to 1994. The Octave method always resulted in an underestimation. Diversity indices, Shannon's H, Simpson's D and , Hurlbert's E(Sn), Itow's b, and Morisita's H gave good estimates when the number of counts was five or more. Temporariness of univoltine species in flight period made a bias in the estimates. We concluded that the count is needed at least six times (once a month) and the estimates were improved by separating the multivoltine species from the univoltine species. Intensive counting during the flight period of the univoltine species was recommended.     

Trends in abundance of tropical forest insects

Summary The stability of a large variety of insect populations was studied using 14 years of light-trap data collected in a relatively undisturbed tropical forest in Panama. Special emphasis was placed on trends in abundance over time. A large between-species variation was found in stability, ranging from nearly constant to violently fluctuating. Over a 14-year period 22% of the species with more than 26 individuals caught showed an average trend of more than 10% of their mean abundance per year, and 4% a trend of more than 20% per year. Even among the 78 species represented by more than 1000 individuals, 7 species, 9%, showed a trend of more than 10% of mean abundance per year. These results appear to be incompatible with the generally held tenet that natural populations in undisturbed environments fluctuate within rather narrow abundance limits, and may indicate that at least a certain proportion of natural populations are not kept within such limits by regulatory processes. Actual fluctuating patterns vary a great deal between species, suggesting the absence of some dominant environmental process affecting several species at the same time. The total number of species and individuals, and the associated value of the -diversity index remained at the same level over the 14 years.     

Estimating population density from indirect sign: track counts and the Formozov–Malyshev–Pereleshin formula

For many purposes it is often desirable to estimate animal population densities over large areas. Where total counts are not possible and sightings are relatively rare, a range of methods exists to estimate densities from indirect sign. Such methods are frequently unreliable and usually require independent calibration or confirmation. We present an analytical method for estimating population density from track counts. The method, widely known in the Russian Federation but not in the English language scientific literature, requires counts of tracks of known age, together with estimates of animal daily travel distances. We use simulations to verify the theoretical basis of the approach and to indicate potential precision that may be achieved. We illustrate application of the approach using a large data set on ungulate track counts in the Russian Far East. We suggest that under most circumstances, nonparametric bootstrapping will be the most appropriate method for deriving estimates of confidence intervals about density estimates. As with other approaches to estimating density from indirect sign, the method that we discuss is vulnerable to violations of an array of underlying assumptions. However, it is easily applied and could represent an important method by which the relationship between indices of abundance and absolute density can be understood.     

The importance of shelter for butterflies in open landscapes

In Britain, much emphasis has been placed on conserving butterfly species in specialized habitats, since this is where most of its threatened butterflies exist, whilst the wider countryside has been largely overlooked. However, there is increasing awareness that small improvements to the dominant landscape could potentially reap huge benefits to the populations of many of Britains butterfly species. Recent studies have also stressed the importance of the landscape scale in the conservation of butterflies in small fragmented habitats. In this paper, we examine data from a variety of sources and conclude that the importance of shelter in open landscapes may be underestimated since recording is often restricted to the optimum conditions suggested by the Butterfly Monitoring Scheme. In less favourable conditions, butterflies may place greater reliance on those components of the landscape offering shelter. In light of the current policy of agricultural de-intensification we discuss how modifications to our current landscapes could benefit a wide range of species.     

A new methodology for compiling national Red Lists applied to butterflies (Lepidoptera, Rhopalocera) in Flanders (N-Belgium) and the Netherlands

The compilation of the Red Lists of butterflies in Flanders and the Netherlands was based on two criteria: a trend criterion (degree of decline) and a rarity criterion (actual distribution area). However, due to the large difference in mapping intensity in the two compared periods, a straightforward comparison of the number of grid cells in which each species was recorded, appeared inappropriate. To correct for mapping intensity we used reference species that are homogeneously distributed over the country, that have always been fairly common and that did not fluctuate in abundance too much during this century. For all resident species a relative presence in two compared periods was calculated, using the average number of grid cells in which these reference species were recorded as a correction factor. The use of a standardized method and well-defined quantitative criteria makes national Red Lists more objective and easier to re-evaluate in the future and facilitates the comparison of Red Lists among countries and among different organisms. The technique applied to correct for mapping intensity could be useful to other organisms when there is a large difference in mapping intensity between two periods.     

Management of threatened insect species in Australia, with particular reference to butterflies

Abstract   Advances in determination of conservation status of insects through evaluation of threats (rather than simple 'rarity' alone) help to set priorities for allocation of conservation resources, and formulate effective legislative treatment and field management for the most needy species. Summaries of several recent conservation studies on butterflies exemplify the variety of practical needs, amongst which habitat protection and enhancement is paramount. However, the paucity of biological and distributional information on most Australian insects necessitates considerable flexibility in approach, so that perceptions of conservation need may be highly subjective. Listing species for protection and conservation priority must be viewed as a dynamic process, with opportunity for rapid action, either to list or de-list taxa as research and recovery actions lead to change in perceived or real status and conservation need.     

Fluctuations of Vanessa cardui butterfly abundance with El Niño and Pacific Decadal Oscillation climatic variables

Annual 4th of July Butterfly Count data spanning more than 20 years are examined to explore Vanessa cardui (Painted Lady) population fluctuations with ENSO (El Niño) and Pacific Decadal Oscillation (PDO) indices. California, Colorado and Nebraska censuses exhibit a strong positive correlation with the strong El Niño events of 1982–1983 and 1997–1998 and the weaker event of 1991–1992. Regression analysis shows the population fluctuations are strongly coupled to climate variations on both short (El Niño) and longer (Pacific Decadal Oscillation) time scales. Recognizing the sensitivity to these time scales is important for predicting longer‐term global climate change effects.     

Comparisons of butterfly richness and abundance measures in prairie and barrens

Transect surveys of adult butterflies were conducted along fixed routes at 27 study sites grouped into three subregions of tallgrass prairie and one subregion of pine-oak barrens in the midwestern USA. Within subregion, each site was visited the same number of times over 5–7 years on similar dates with similar weather. For each site, five indices of species richness and/or abundance were calculated both for total butterflies and for specialist species primarily restricted to native herbaceous vegetation. These indices were then analysed as to how much they agreed or conflicted in site ranking and how site rankings based on total butterflies compared to those based on specialists. Variation in site ranking by different indices was relatively low. Mean site rank by specialist indices covaried significantly with mean site rank by indices for total butterflies. Numerous studies have shown that on a regional scale, areas of higher richness for all species in a taxonomic group are different habitat types (based on amount of canopy or degree of degradation) from hotspots for that taxon's subset of species of conservation concern (endemics or specialists). But in this study, within a habitat type, site rankings based on total butterflies significantly tended to agree with site rankings based on specialist butterflies. This suggests that site prioritization and management favouring specialist butterflies would also favour the overall butterfly fauna possible in the same habitat.     

Egg weight variation in relation to egg mortality and starvation endurance of newly hatched larvae in some satyrid butterflies

Abstract. 1. Egg weights decrease over the oviposition period in all of the five satyrid butterflies that have been studied, viz Parage aegeria L., Lasiommata petropolitana F., L.maera L., L.megera L. and Lopingaachine Scop. However, within each species, no correlation was found between variation in egg weight and egg mortality in 30% relative humidity or the ability of newly hatched larvae to survive without food for 1–4 days. 2. Although egg weights of Papilio machaon L. were similar to the highest satyrid egg weights, newly hatched larvae of P.machaon showed significantly higher mortality after 1 day of starvation when compared to all of the satyrid larvae. This indicates that the capability of newly hatched larvae to endure starvation is not necessarily correlated with egg weight, and consequently that this character trait of satyrid larvae has been selected for (i.e. should be regarded as an adaptation). It is noteworthy that this ability of satyrid larvae to endure starvation is coupled with the habit of many satyrid butterflies not to deposit their eggs directly on the larval host plants. 3. In 30% relative humidity, egg mortality of L.achine was 100% and that of P.aegeria 29.2%, whereas that of the three Lasiommata spp. was significantly lower. At 100% relative humidity egg mortality in L.achine dropped to 8%. Since egg weights are higher in L.achine than in the other four satyrids this indicates that egg resistance to desiccation is not necessarily correlated with egg size (as might be expected due to the area to volume ratio which is negatively correlated with egg size). Thus the resistance to desiccation which is found in the three Lasiommata spp. should be regarded as an adaptation to the habit of these three butterflies to deposit their eggs in relatively dry microhabitats. This resistance to desiccation is not found in eggs of the two forest-dwelling satyrids P.aegeria and L.achine which lay their eggs in microhabitats where the relative humidity is high.     

Distribution of edaphic-endemic butterflies in the Sierra Nevada of California

Five edaphically-restricted or -endemic butterflies, mostly associated with serpentine, are shown to be distributed in the western foothills of the Sierra Nevada in addition to their previously documented areas of occupancy in the California North Coast Ranges. Two species are absolutely limited by the edaphic restriction of their host plants, while the other three seemingly are not. The controversies concerning the origins of serpentine endemism in plants apply to butterflies as well. Long-term relictualism can presumably apply only at the metapopulation level, not the local population level, due to the frequency of fire in these habitats. Development and habitat-conversion trends pose a high risk to the long-term survival of these species in the Sierra Nevada.     

Effects of climatic change on the phenology of butterflies in the northwest Mediterranean Basin

Phenological changes in response to climatic warming have been detected across a wide range of organisms. Butterflies stand out as one of the most popular groups of indicators of climatic change, given that, firstly, they are poikilothermic and, secondly, have been the subject of thorough monitoring programmes in several countries for a number of decades. Here we provide for the first time strong evidence of phenological change as a consequence of recent climatic warming in butterflies at a Spanish site in the northwest Mediterranean Basin. By means of the widely used Butterfly Monitoring Scheme methodology, three different phenological parameters were analysed for the most common species to test for trends over time and relationships with temperature and precipitation. Between 1988 and 2002, there was a tendency for earlier first appearance dates in all 17 butterfly species tested, and significant advances in mean flight dates in 8 out of 19 species. On the other hand, the shape of the curve of adult emergence did not show any regular pattern. These changes paralleled an increase of 1–1.5°C in mean February, March and June temperatures. Likewise, a correlation analysis indicated the strong negative effect of spring temperature on phenological parameters (i.e. higher temperatures tended to produce phenological advances), and the opposite effect of precipitation in certain months. In addition, there was some evidence to indicate that phenological responses may differ between taxonomic lineages or species with similar diets. We discuss the consequences that these changes may have on species' population abundances, especially given the expected increase in aridity in the Mediterranean Basin caused by current climatic warming. We predict that varying degrees of phenological flexibility may account for differences in species' responses and, for multivoltine species, predict strong selection favouring local seasonal adaptations such as diapause phenomena or migratory behaviour.     

Factors influencing the abundance of Japanese encephalitis vectors in ricefields in India – I. Abiotic

Mosquitoes of the Culex vishnui subgroup (Diptera: Culicidae) are the most important vectors of Japanese encephalitis (JE) and ricefields are their most productive breeding sites in south India, where predominant species of this subgroup are Culex tritaeniorhynchus Giles, Cx. pseudovishnui Colless and Cx. vishnui Theobald sensu stricto. The relationship of 13 abiotic variables with the abundance of Cx. vishnui subgroup immatures was investigated in transplanted rice fields for 3 years (1991-94) covering three different crop seasons. The results from the multiple regression model suggested paddy height (- ve), water temperature (+ ve), dissolved oxygen (- ve), ammonia nitrogen (- ve) and nitrate nitrogen (+ ve) to be the best predictor variables associated with the immature abundance, nearly always consistent in their effects within and between seasons. Application of synthetic nitrogenous fertilizers to the rice fields was followed by a rise in concentration of ammonia nitrogen and a subsequent increase in nitrate nitrogen level in the rice field water, during which an increase in the density of larval instars was observed.     

DNA-based confirmation that the parasitic wasp <Emphasis Type="Italic">Cotesia glomerata</Emphasis> (Braconidae,Hymenoptera) is a new threat to endemic butterflies of the Canary Islands

Island-endemic species can be particularly vulnerable to alien invasion. There are many examples of introduced insect parasitoids having a serious impact on endemic butterflies and moths. In 2006, a population of parasitic wasps was reared from larvae of the Canary Island Large White butterfly (Pieris cheiranthi), an endemic inhabitant of laurel forests unique to the Canary Islands of Macaronesia. Parasitoids were tentatively identified as Cotesia glomerata (Braconidae, Hymenoptera), a widely introduced agricultural bioagent. To corroborate this finding we sequenced 632 bp of mitochondrial cox1 from parasitoids and hosts from La Palma and from the native range of C. glomerata in continental Europe. These were combined with GenBank sequences and a character-based, phylogenetic approach was used to assess the species status of parasites and hosts. The La Palma parasitoid could unambiguously be assigned to C. glomerata under the criterion of diagnosibility with corroboration from multiple lines of evidence (DNA, morphology). We suggest that this opportunistic, non-native parasitoid wasp will be a threat to P. cheiranthi and other endemic Canarian butterflies. Parasitoid populations were recorded from P. cheiranthi in marginal forest habitats but not in central forest areas, suggesting that comprehensive habitat conservation of the Canarian laurel forests could prevent penetration of the alien parasitoid wasps and subsequent mortality of endemic butterfly populations.     

Density, climate and varying return points: an analysis of long-term population fluctuations in the threatened European tree frog

Experimental research has identified many putative agents of amphibian decline, yet the population-level consequences of these agents remain unknown, owing to lack of information on compensatory density dependence in natural populations. Here, we investigate the relative importance of intrinsic (density-dependent) and extrinsic (climatic) factors impacting the dynamics of a tree frog (Hyla arborea) population over 22 years. A combination of log-linear density dependence and rainfall (with a 2-year time lag corresponding to development time) explain 75% of the variance in the rate of increase. Such fluctuations around a variable return point might be responsible for the seemingly erratic demography and disequilibrium dynamics of many amphibian populations.     

Surveys of diseases of spring barley in England and Wales, 1976–1980

Samples from 200–300 randomly selected spring barley crops were taken annually at growth stage 73–77 (milky ripe) from 1976 to 1980. The number of samples from each region was proportional to the area of barley grown in each region. The percentage of the area of the top two leaves affected by diseases was recorded. Mildew (Erysiphe graminis) was the most widespread and severe disease recorded. Brown rust (Puccinia hordei) and rhynchosporium (Rhyn-chosporium secalis) occurred frequently but at relatively low levels. Yellow rust {Puccinia striiformis) and septoria (Septoria nodorum) were seen on less than 50% of the samples in most years, and halo spot (Selenophoma donacis) and net blotch (Pyrenophora teres) were rarely recorded. There was an association between the severity of rhynchosporium and the number of rain days in May and June. The highest levels of brown rust occurred in the south and east and rhynchosporium was more common in Wales and the south-west than in the east, but there were no differences in the regional distribution of other diseases. Cultivar resistance, sowing date, previous cropping and fungicide usage were all found to be associated with altered disease levels. The proportion of crops treated with a foliar fungicidal spray rose from 26% in 1976 to 47% in 1980. The use of tridemorph declined but that of triadimefon increased reaching 29% of crops treated by 1980. The use of ethirimol as a seed treatment declined from 16% of crops grown from treated seed in 1976 to 7% in 1980. Estimated yield losses between 1976 and 1980 varied between 4% and 9% due to mildew, between 0.3% and 0.8% due to brown rust and between 0.2% and 0.5% due to rhynchosporium.     

Comparative morphology of the prothoracic leg in heliconian butterflies: Tracing size allometry,podite fusions and losses in ontogeny and phylogeny

Prothoracic legs of heliconian butterflies (Nymphalidae, Heliconiinae, Heliconiini) are reduced in size compared to mesothoracic and metathoracic legs. They have no apparent function in males, but are used by females for drumming on host plants, a behavior related to oviposition site selection. Here, taking into account all recognized lineages of heliconian butterflies, we described their tarsi using optical and scanning electron microscopy and searched for podite fusions and losses, and analyzed allometry at the static, ontogenetic and phylogenetic levels. Female tarsi were similar, club-shaped, showing from four to five tarsomeres, each bearing sensilla chaetica and trichodea. Male tarsi were cylindrical, formed from five (early diverging lineages) to one (descendant lineages) either partially or totally fused tarsomeres, all deprived of sensilla. Pretarsi were reduced in both sexes, in some species being either vestigial or absent. Tarsal lengths were smaller for males in almost all species. An abrupt decrease in size was detected for the prothoracic legs during molting to the last larval instar at both histological and morphometric levels. In both sexes, most allometric coefficients found at the population level for the prothoracic legs were negative compared to the mesothoracic leg and also to wings. Prothoracic tarsi decreased proportionally in size over evolutionary time; the largest and smallest values being found for nodes of the oldest and youngest lineages, respectively. Our results demonstrate that evolution of the prothoracic leg in heliconian butterflies has been based on losses and fusions of podites, in association with negative size allometry at static, ontogenetic and phylogenetic levels. These processes have been more pronounced in males. Our study provided further support to the hypothesis that evolution of these leg structures is driven by females, by changing their use from walking to drumming during oviposition site selection. In males the leg would have been selected against due to absence of function and thus progressively reduced in size, in association with podites fusions and lost.