The downfall of mating: the effect of mate-carrying and flight muscle ratio on the escape ability of a pierid butterfly

In many species, the ability to evade predators is known to be periodically impaired by increased weight loads due to feeding and reproduction. Not only may extra weight reduce escape speed, but feeding and mating can also make the prey more noticeable to visually hunting predators. A number of butterfly species mate for hours, and if a mating couple is disturbed, one of the butterflies is responsible for flying, whereas its partner remains still. This study investigated the ability of male Pieris napi butterflies to fly while mating, with the prediction that mate carrying impairs flight ability compared to single flying males and that males with relatively high flight muscle ratios (FMR; male thorax mass/male + female body mass) will have better flight performance in copula. Our results clearly show that whereas single males always take off at steep angles and fly upwards, couples invariably have a negative take-off angle and rarely gain height. Moreover, landing height of the couples is positively associated with higher FMR. Hence, male flight ability when in copula is positively associated with a high relative thorax mass. Butterfly pairs may thus be at greater risk of predation as a consequence of their impaired flight ability, especially couples with critically low FMRs (<16%).     

Effects of irrigation and landscape heterogeneity on butterfly diversity in Mediterranean farmlands

Irrigation effects on biodiversity are poorly known, particularly in Mediterranean agro-ecosystems. In this study we analyzed irrigation effects on butterfly species richness, abundance and diversity as well as on species composition in a farmed landscape under Mediterranean climate. The study area consisted of four contiguous agricultural sub-areas with a decreasing degree of intensification: irrigated, mixed (dry and irrigated), dry and environmentally protected (i.e. Special Protection Area, SPA) dry farmland. Forty one km-transects (ten per sub-area) were searched for butterflies in 2008 and 2009. Contrary to expectations, species richness (alfa, beta and gamma diversity) was highest in both years in the most intensified sub-area (i.e. irrigated) followed by SPA, dry and mixed sub-areas. Landscape characteristics accounted for most of the between-subareas differences in species richness. Species richness was negatively related to mean field size at the landscape level and positively related to the number of trees and large shrubs along transects. Therefore, the higher number of butterfly species recorded in the irrigated farmland could be due to a more complex landscape. In contrast, butterfly abundance was highest in cereal steppes (i.e. dry and SPA sub-areas), with abundance being negatively affected by mean field size. Inter-annual change in butterfly abundance was much sharper in rainfed (i.e. dry and SPA) than in irrigated (i.e. irrigated and mixed) sub-areas. Irrigated farmland may provide more favorable conditions for butterflies by buffering the (year-to-year and summer) drought periods characterising Mediterranean climate. Species composition differed among sub-areas, with differences being partly explained by field size and number of trees and shrubs along transects. Our study suggest an important role of landscape characteristics in boosting butterfly biodiversity in intensively managed irrigated croplands and emphasizes the importance of encouraging studies on farmland butterfly diversity in different (bioclimatic) regions allowing the design of region-specific agri-environmental schemes.     

Maximum likelihood fitting of the Poisson lognormal distribution

In this paper some properties and analytic expressions regarding the Poisson lognormal distribution such as moments, maximum likelihood function and related derivatives are discussed. The author provides a sharp approximation of the integrals related to the Poisson lognormal probabilities and analyzes the choice of the initial values in the fitting procedure. Based on these he describes a new procedure for carrying out the maximum likelihood fitting of the truncated Poisson lognormal distribution. The method and results are illustrated on real data. The computer program for calculations is freely available.

Monitoring the Response of Butterfly Communities to Prescribed Fire

Federal land managers in the western United States are interested in the potential of prescribed fire as a tool to decrease fuel loads, increase vegetational heterogeneity, and increase faunal diversity in various ecosystems. I tested whether implementation of a prescribed fire program by the US Forest Service in a watershed in the central Great Basin had significant effects on butterfly species richness and composition. I monitored butterfly communities during the first two years after implementation in five to seven burn units and controls in the watershed. To estimate baseline spatial and temporal variation in butterfly communities in the greater ecosystem, I also monitored butterflies in five untreated canyons outside the project area. Butterfly species richness and butterfly species composition (measured as community similarity) did not differ significantly between burn units and controls. Geographic location had statistically significant effects on species richness. Butterfly species composition of individual locations varied over time, as did the magnitude of that variation. These results emphasize that standardized, repeatable monitoring protocols are vital for evaluating the effects of experimental management treatments and for predicting and assessing the effects of future management strategies and environmental changes.