There are many facets of behavioral ecology. This lecture continued discussion of this topic using a particular research system, California checkerspot butterfly (Euphrydryas editha) populations to illustrate the connection between behavior and the spatial structure of a population.

I compared the life history and ecology of two editha populations it the San Fransisco Bay Area. In that region this insect occurs only in habitats with serpentine soil.

1) At Jasper Ridge, Stanford University's "BFL", a serpentine outcrop supports editha's specific host plants. These have been eliminated on good soils by invading Mediterranean weeds such as annual grasses from Spain. Adult editha emerge in spring (March), mate, and begin feeding on various nectar producing flowers which mass bloom for a few weeks until things dry up (in the Mediterranean climate the onset of the dry season is in late spring and the summers are very dry).

During their brief life span (5-10 days) female editha search for a specific plant, Plantago erecta (small greenish flowers), for depositing their egg clusters. Later, well after the last female has died, most young caterpillars in the population are left without food when P. erecta dries up and dies. While they were developing another host plant, Orthocarpus, a pink-flowered root parasite, was growing in the grassland. Hungry editha searching for food are saved if they find Orthocarpus since it stays succulent into the dry late spring. Editha developing to 3rd instar are then able to enter an obligatory summer diapause, a resting stage which allows the larva to survive even several years without feeding. When rains return in mid fall Plantago begins to grow and by January post-diapause editha larvae can be found feeding on sunny days. They are black and spend lots of time basking in the winter sun to raise body temperature to that required for activity. They pupate in February and emerge again in March.

At Jasper Ridge adult nectar plants and larval hosts (Plantago and Orthocarpus) occur interspersed in spectacular "flower shows" on patches of serpentine. Males can cruise from flower to flower looking for receptive females along the way. Females likewise can alternatively search for Plantago or nectar plants along the same flight path. In 1961 Ehrlich described "intrinsic barriers to dispersal" in the editha populations on Jasper Ridge noting that the vast majority of recaptures of marked adults occured within original patch of capture rather than in closely adjacent patched separated by unsuitable habitat. We now ascribe this tendency of highly mobile individuals to "stay home" to the fact that given the complexity of recognizing suitable combinations of host plant at that site individuals do best by staying where other individuals are encountered. This leads to the negative density dependent dispersal mentioned in the first lecture.

Travelling to the South and West of Stanford near Livermore is a dry mountain range. The bay race of editha also occurs there in Del Puerto Canyon. Interestingly this habitat also has a serpentine soil but everything else is different. Adult flight period is later than at Jasper Ridge even though the area is hotter and drier. While editha lives in a grassland at Jasper Ridge, at Del Puerto the habitat is chaparral (low shrubbery). Although several potential host plants for larvae are present at Del Puerto, only one, Pedicularis, a perennial parasite of shrubs and small trees like madrone is used for egg deposition and larval development. These plants, and thus larvae, pupae and new hatching adults are distributed near the top of the slopes above the canyon.

In contrast to Jasper Ridge, adult nectar resources at Del Puerto are disjunct from larval hosts. Adult editha must fly several hundred feet down the mountain to visit flowering shrubs along the creek below. Thus, both sexes must travel down to the creek to forage for nectar. Males, to find and compete for newly hatching virgins, must maximize time around larval hosts on the ridges above the creek, travelling down for nectar only when necessary. Females in contrast, can easily locate larval hosts and can allocate more time to competing for nectar along the creek. Recaptures of marked individuals show that editha at Del Puerto not only move more widely than Jasper Ridge adults, but the sexes exhibit substantial differences in proportions of time spent in different parts of the area occupied by the population. These behavioral differences are adaptations to different spatial and temporal arrangements of resource plants in the two contrasting habitats. Long standing ecological differences between habitats can lead to microevolution of dispersal behavior which in turn determines the picture we obtain about the population from mark release studies. We can expect the Del Puerto editha to colonize suitable habitats more readily because it has reason not to respect extrinsic barriers(such as habitat with out resource plants).

I recommend that you read the paper from American Naturalist on reserve in the science library (Gene flow and dispersal in a butterfly species).