Alan E. Launer

Butterfly diversity and human land use: Species assemblages along an urban gradient

Abstract We examined the distribution and abundance of butterfly species across an urban gradient and concomitant changes in community structure by censusing the butterfly and skipper populations at 48 points within six sites near Palo Alto, California, USA (all former oak woodlands). These sites represent a gradient of urban land use running from relatively undisturbed to highly developed and include a nature preserve, recreational area, golf course, residential neighborhood, office park and business district. The species richness and Shannon diversity of butterflies peaked at moderately disturbed sites while the relative abundance decreased from the natural to the urban areas. Butterfly species thought to be most representative of the original, predevelopment butterfly fauna progressively disappear as the sites become more urban. These patterns are significantly related to shifts in habitat structure that occur along the gradient as determined by canonical correspondence analysis (CCA) using the environmental variables of percent land covered by pavement, buildings, lawn, grasslands, and trees or shrubs. The mechanisms behind these patterns may be related to life history and resource use by the individual butterfly species.

The role of adult feeding in egg production and population dynamics of the checkerspot butterfly Euphydryas editha

Carbohydrate intake increases longevity, body weight maintenance and egg production in female Euphydryas editha. Amino acid intake leads to heavier eggs, larvae from which are more likely to survive. Females fed nectar produce more eggs in later masses than females which are not fed. During years of normal and below normal precipitation, larvae emerging from these later eggs are unlikely to reach obligatory size for diapause before their food dries up. On Jasper Ridge, where mortality is density-independent, nectar plays an important role increasing production of late egg masses during years of greater than normal rainfall when larvae from these masses are likely to reach diapause. The resulting large population increases, though infrequent, are probably important in maintaining population sizes large enough to reduce the chances of extinction during dry years.

Emergence patterns in male butterflies: A hypothesis and a test

Abstract A game theoretical model is advanced to explain the emergence time schedule of male butterflies under temporal “apostatic” selection, so that males emerging on different days enjoy equal fitness in evolutionary equilibrium. The model predicts not only the position of the peak date but also the shape of the male emergence curve for any given female emergence schedule. Where the female emergence curve is smooth with one peak, a flight season can be divided into an earlier phase, when some males emerge every day, and a later phase in which no male emerges. The male emergence curve is truncated at the boundary of the phases. The position of the truncation point is determined by the difference between pre- and postemergence mortality. Preemergence mortality also determines the rate coefficient of the decrease in sex ratio through the season. The model is applied to a well-studied population of the butterfly Euphydryas editha. The male presence curve fits well, but no clear truncation exists in male emergence, and some males emerge earlier than predicted. Reasons for deviations are discussed.

Identifying Extinction Threats

Relatively pristine habitats around the world are being lost at unprecedented rates (Melillo et al. 1985, Skole and Tucker 1993) as an expanding human population converts them to agriculture, forestry, and urban centers (Hall 1978, Vitousek et al. 1986). As these habitats are altered, untold numbers of species are disappearing before they have been recognized, much less studied (Wilson 1989), and the functioning of entire ecosystems is threatened. This loss of biodiversity, at the very time when the value of biotic resources is becoming widely recognized (Malone 1992), has made it strikingly clear that current strategies for conservation are failing dismally (Ehrlich 1992, Ehrlich and Wilson 1991).

Umbrella species and the conservation of habitat fragments: A case of a threatened butterfly and a vanishing grassland ecosystem

The serpentine soil-based grasslands of central California and severely threatened by non-native plant species and suburban sprawl. At the present time only one animal species restricted to this community, the Bay checkerspot butterfly Euphydryas editha bayensis, is protected by the United States Endangered Species Act. This study examined the distribution of the butterfly and native grassland plant species across 27 habitat patches in the San Francisco Bay area in an effort to determine the value of the butterfly as an ‘umbrella species’. Conservation activities designed for the Bay checkerspot butterfly were found to provide a tenuous protective umbrella for other elements of the grassland community. If all sites presently occupied by the butterfly were preserved intact, upwards of 98% of the native spring-flowering plant species would receive some measure of protection. However, if only the sites supporting the largest butterfly populations are preserved, or if portions of habitat patches classified as being of ‘marginal’ value to the butterfly are lost, then the proportion of plant species receiving protection drops substantially.

Identifying Extinction Threats: Global Analyses of the Distribution of Biodiversity and the Expansion of the Human Enterprise

Relatively pristine habitats around the world are being lost at unprecedented rates (Melillo et al. 1985, Skole and Tucker 1993) as an expanding human population converts them to agriculture, forestry, and urban centers (Hall 1978, Vitousek et al. 1986). As these habitats are altered, untold numbers of species are disappearing before they have been recognized, much less studied (Wilson 1989), and the functioning of entire ecosystems is threatened. This loss of biodiversity, at the very time when the value of biotic resources is becoming widely recognized (Malone 1992), has made it strikingly clear that current strategies for conservation are failing dismally (Ehrlich 1992, Ehrlich and Wilson 1991).

CAN SEX RATIO BE DEFINED OR DETERMINED? THE CASE OF A POPULATION OF CHECKERSPOT BUTTERFLIES

The sex ratio of adults in a single generation in a demographic unit of Euphydryas editha was strongly skewed toward males. This appears to be caused by higher pre-adult mortality in females, a higher rate of female emigration, and possibly higher female adult mortality. The impact of this and related factors on determining Ne is discussed. Although Ne in E. editha populations generally appears to be far below twice the number of males, it also seems to be well above the range where drift would be expected to be a major evolutionary factor. It is suggested that the factors that skew sex ratio and reduce Ne in E. editha may well operate in other univoltine insects.

Do hypotheses from short-term studies hold in the long-term? An empirical test

Abstract. 1. A sequence of population estimates for two now‐extinct populations of Euphydryas editha bayensis is presented. After removing biased sampling days, estimates of demographic parameters from the long‐term data were used to test five hypotheses built from studies of shorter duration. Such tests of short‐term conclusions are rare.

Genetic Structure And Demography Of Chloropyron palmatum, An Endangered Annual Plant

Abstract Chloropyron palmatum (Ferris) Tank & J.M Egger (formerly Cordylanthus palmatus [Ferris] J. F. Macbr.) is an annual plant that inhabits seasonally flooded wetlands with saline and alkaline soils in California. In 1986, the plant was listed as endangered under the U.S. Endangered Species Act. We aimed to inform conservation strategies for the species’ five remaining populations by examining the genetic diversity and structure of the populations (on the basis of nuclear DNA markers) and their potential response to demographic and environmental stochasticity. We also assessed fluctuations in population size and whether there was evidence of hybridization between C. palmatum and Chloropyron molle (A. Gray) A. Heller subsp. hispidum (Pennell) Tank & J.M. Egger (formerly Cordylanthus mollis A. Gray subsp. hispidus [Pennell] T.I. Chuang & Heckard). Populations of C. palmatum were genetically distinct with a FST of 0.23, indicating substantial genetic structure among populations. Within populations, there was no evidence of isolation by distance. However, individuals in two adjacent vernal pools were genetically distinct. The pattern of genetic variation within populations suggests that the historical frequency and extent of seed dispersal by overland flooding has strongly affected the genetic structure of populations. Despite founder effects and population bottlenecks, small and large populations had similar levels of genetic variation. We found no evidence of hybridization. All extant populations of C. palmatum are genetically variable and distinct. We recommend that hydrologic connectivity be considered if seeds are collected and sowed with the intent of increasing the size of natural populations or creating experimental populations.

Use of stochastic patch-occupancy models in the California red-legged frog for Bayesian inference regarding past events and future persistence

Abstract Assessing causes of population decline is critically important to management of threatened species. Stochastic patch occupancy models (SPOMs) are popular tools for examining spatial and temporal dynamics of populations when presence–absence data in multiple habitat patches are available. We developed a Bayesian Markov chain method that extends existing SPOMs by focusing on past environmental changes that may have altered occupancy patterns prior to the beginning of data collection. Using occupancy data from 3 creeks, we applied the method to assess 2 hypothesized causes of population decline—in situ die‐off and residual impact of past source population loss—in the California red‐legged frog. Despite having no data for the 20–30 years between the hypothetical event leading to population decline and the first data collected, we were able to discriminate among hypotheses, finding evidence that in situ die‐off increased in 2 of the creeks. Although the creeks had comparable numbers of occupied segments, owing to different extinction–colonization dynamics, our model predicted an 8‐fold difference in persistence probabilities of their populations to 2030. Adding a source population led to a greater predicted persistence probability than did decreasing the in situ die‐off, emphasizing that reversing the deleterious impacts of a disturbance may not be the most efficient management strategy. We expect our method will be useful for studying dynamics and evaluating management strategies of many species.