Dennis D. Murphy

SUN, SLOPE, AND BUTTERFLIES: TOPOGRAPHIC DETERMINANTS OF HABITAT QUALITY FOR EUPHYDRYAS EDITHA'

Thermal environments in a large, topographically diverse serpentine soil- based grassland were quantified and ranked using a computer model of clear sky insolation and shading on different slopes to determine the effects of microclimate on the rates of development of each of the life stages of the butterfly Euphydryas editha bayensis. Larvae developed to pupation earlier on warm slopes than on progressively cooler slopes. Avail- ability of sunlight can be limiting for larvae, which bask in direct sun to raise body temperature. Larvae can disperse > 10 m/d, allowing them to transfer between microcli- mates. Pupae on warmer slopes also developed faster than those on cooler slopes. Microclimate also affects the phenology of host plants of larvae and nectar sources of adults. Larval and pupal development and host-plant phenology determine the phase relationship between adult butterfly flight and host-plant senescence, which in turn deter- mines mortality rates of prediapause larvae. Adult females that eclosed early in the season could have their offspring survive on almost all slopes; survivorship of offspring from adults that eclosed in the middle of the flight season was restricted to cooler slopes in the habitat. Some butterflies eclosed too late for their offspring to survive on any slope. Topographic diversity on several scales is a prime indicator of habitat quality for this butterfly. Areas of high local topographic diversity on a scale of tens of metres appear particularly important for long-term population persistence under variable climatic condi- tions.

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.

A NEW METHOD FOR SELECTION OF UMBRELLA SPECIES FOR CONSERVATION PLANNING

Umbrella species, species whose protection serves to protect many co-occurring species, have been proposed as a shortcut for conservation planning. Potential criteria for selection of umbrella species include rarity, sensitivity to human disturbance, and mean percentage of co-occurring species. Using butterflies in montane canyons in the Great Basin (USA) as a case study, we examined correlations among those three selection methods. We also developed a new index that specifically ranks species according to their potential to serve as umbrellas for their taxonomic group. Different methods for prioritizing species generally produced divergent rankings. Although rare butterflies tended to co-occur with more species than widespread butterflies, rare species may be poor umbrellas because their distributions are too highly restricted and often cannot be influenced by managers. Umbrella species are useful in meeting certain conservation challenges, particularly prioritization of habitat remnants for conservation...

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.

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.

A realistic assessment of the indicator potential of butterflies and other charismatic taxonomic groups.

Charismatic groups of animals and plants often are proposed as sentinels of environmental status and trends. Nevertheless, many claims that a certain taxonomic group can provide more-general information on environmental quality are not evaluated critically. To address several of the many definitions of indicator species, we used butterflies to explore in some detail the attributes that affect implementation of indicators generically. There probably are few individual species, or sets of species, that can serve as scientifically valid, cost-effective measures of the status or trend of an environmental phenomenon that is difficult to measure directly. Nevertheless, there are species with distributions, abundances, or demographic characteristics that are responsive to known environmental changes. In this context, single or multiple species can serve as indicators when targets are defined explicitly, ecological relationships between the target and the putative indicators are well understood, and data are sufficient to differentiate between deterministic and stochastic responses. Although these situations exist, they are less common than might be apparent from an extensive and often confounded literature on indicators. Instead, the public appeal of charismatic groups may be driving much of their acclaim as indicators. The same taxon may not be appropriate for marketing a general conservation mission and for drawing strong inference about specific environmental changes. To provide insights into the progress of conservation efforts, it is essential to identify scientific and practical criteria for selection and application of indicators and then to examine whether a given taxonomic group meets those criteria.

Nectar source distribution as a determinant of oviposition host species in Euphydryas chalcedona

The distribution of nectar sources is shown to affect both the distribution of adult Euphydryas chalcedona and their offspring. We suggest that nectar sources thereby influence the selection of oviposition host plant species in habitats where those species are spacially separated.

Nestedness analysis and conservation planning: the importance of place, environment, and life history across taxonomic groups

Abstract. We used nested subsets analysis to examine distribution patterns of birds and butterflies in the same set of 83 locations in canyons of three mountain ranges in the Great Basin of western North America. We tested whether the same environmental variables influenced nestedness among taxonomic groups and among mountain ranges within taxonomic groups. We also examined whether nestedness of birds and butterflies appeared to be sensitive to human use of riparian areas in the ecoregion. Site area and topography did not appear to differ in their influence on nestedness of birds. By contrast, area and topography differed in how strongly they affected nestedness of butterflies, but their respective influence varied among mountain ranges. Riparian dependence had little discernible effect on nested distribution patterns of either taxonomic group. Because processes influencing distribution patterns can differ among taxonomic groups, and the relative importance of those processes may vary spatially even within a taxonomic group, we urge restraint in using birds and butterflies as surrogates of other taxa for conservation planning.

Insular biogeography of the montane butterfly faunas in the Great Basin: comparison with birds and mammals

SummaryButterfly species lists were assembled for 18 Great Basin mountain ranges for which distributional data on mammals and birds have been analysed previously by other workers. The ranges represent remnant islands of the boreal habitat that once was continuous across the Great Basin but is now restricted to higher elevations as a result of climatic change at the close of the Pleistocene. The effects of biogeographic factors (area, distance, elevation) and habitat diversity on butterfly species number were examined. The Great Basin boreal butterfly faunas were found to be depauperate overall relative that of the principal mainland source, the Rocky Mountains, and were found to have fewer species than predicted by the mainland species-area data. However, only a weak area effect, and no distance effect, was detected by bivariate and multivariate analysis. Furthermore, the habitat diversity score found to explain virtually all the variation in bird species number in the same ranges in previous studies is only marginally significantly correlated with butterflies. When the butterflies are subdivided according to their vagility, the relative differences in the species-area correlation and slope (z-value) between the vagility categories were consistent with those found previously for mammals and birds, and, as predicted by theory, less vagile taxa exhibit higher species-area correlations and z-values. Overall, differences in the insular biogeography of buttterflies and vertebrates seem to reflect fundamental ecological differences between the taxa.

Estimating female reproductive success of a threatened butterfly: influence of emergence time and hostplant phenology

We estimated lifetime reproductive success of Euphydryas editha bayensis (Nymphalidae), a federally listed threatened butterfly, based on age-specific fecundity and both adult and offspring survival. Our results indicate that the relative timing of adult emergence and larval hosplant senescence strongly influenced reproductive success of females. For 1992, we estimated that only 8–21% of the eggs laid by females emerging on the 1st day of the 4-week flight season would produce larvae that reach diapause. This figure dropped to 1–5% for females emerging 7 days into the flight season. Within our entire sample, we estimated that 64–88% of the females produced offspring with less than a 2% probability of reaching diapause. These estimates are particularly striking given that they are based on only one source of larval mortality — prediapause starvation due to hostplant senescence. This dependence of reproductive success on the relative timing of female emergence and hostplant senescence may reduce effective population size and render E. editha bayensis especially vulnerable to local extinction events.