Extinction, reduction, stability and increase: The responses of checkerspot butterfly (Euphydryas) populations to the California drought

Abstract

The California drought of 1975-77 has been correlated with unusual size changes in populations of two species of Euphydryas butterflies. Several populations became extinct, some were dramatically reduced, others remained stable and at least one increased. These differences in population dynamic response are not concordant with predictions made earlier that populations with heavy density-dependent mortality should be more stable in the face of drought than unregulated populations. The different responses are related to the fine details of the relationships between the insects and their host plants, relationships which are variable between populations. Revised predictions are given in the light of better knowledge of the variability and complexity of these insect-host relationships. The diversity of responses underlines the dangers of generalizing about "the ecology" of a taxonomic species. The extinctions support the view that such events are frequent and significant in the biology of populations.

Phenotypic plasticity and population viability: the importance of environmental predictability

“…Empirical studies of wild populations clearly show that stochastic changes in density-independent factors (e.g. weather) can be a major driver of temporal fluctuations in population size (Coulson et al 2001;Stenseth et al 2002) and, in some cases, population extirpations (Ehrlich et al 1980;McLaughlin et al 2002). Yet organisms occupying highly variable environments display a remarkable range of adaptations that allow them to maintain positive fitness across a broad range of conditions, achieved through a combination of homeostatic, plastic and bet-hedging mechanisms (Caswell 1983).…”

Extinction dynamics and the regional persistence of a tree frog metapopulation

“…On the one hand, British butter£y populations do not show an obvious decline in spatial synchrony with distance (Sutcli¡e et al 1996), while on the other, Finnish butter£y populations display substantial asynchrony on a local scale, but seem to be synchronized over the entire metapopulation (Hanski et al 1995). There is also evidence of synchronous butter£y extinctions in response to single climatic events (Ehrlich et al 1980;Pollard & Yates 1993;Sutcli¡e et al 1996;Thomas et al 1996). In this context, it is important to obtain insights into the extent to which local extinctions might be synchronized over wider areas.…”

Determinants of Multiple Host Use by a Phytophagous Insect Population

“…The plants in area 2 have not been affected by burning. A population of E. editha about 50 miles north of Generals' Highway, at Shaver Lake, reached high density feeding on Collinsia in a logged and burned area from 1970 to 1974, but has since become extinct, apparently in response to deterioration of both quality and quantity of its host (Ehrlich et al, 1980). It seems likely that temporary increases in quality of Collinsia as a host of E. editha typically follow logging and burning.…”