Life Histories of Alpine Tundra Arachnida in Colorado

Abstract

Pitfall jars were used to collect 16,342 specimens of spiders, phalangids, erythraeid mites, and ground beetles at 3500-4270 m (11,500-14,000 ft) elevation. Most alpine tundra arachnid species have biennial life cycles, but some are annuals. This biennial pattern also predominates near sea level at high latitudes (50?N+). Annual cycles are more typical of mid-latitude (40?N), low-elevation regions. Various species of alpine tundra Pardosa wolf spiders have either twoor one-year cycles; the length of life appears to be directly proportional to the net primary productivity of the various species habitats. Mating and egg-laying in Pardosa tend to occur later in the year in the alpine tundra than at low elevations. No significant differences in the number of eggs per cocoon in Pardosa were noted when tundra and low-altitude data were compared. The overwintering stages of alpine tundra spiders (young and penultimate juveniles) are the same as for sea level, except that no tundra species overwinter as adults, whereas many low-elevation species do. Pardosa concinna spends its first winter within the cocoon, a novel behavior for a wolf spider. Dramatic temporal changes in the abundance or activity of some carabid ground beetles were recorded from incidental data obtained on this group. INTRODUCTION Relatively little is known about the life histories of arachnids or carabid ground beetles in the alpine tundra. This is particularly true for North America. Since data concerning life histories at lower elevations and in the arctic tundra are relatively more extensive, more research at high altitudes is desirable. In particular, the effects of the seemingly less hospitable alpine tundra environment on life cycle lengths are worth investigating. METHODS AND MATERIALS Nearly all of this research was done between tree line (ca. 3500 m or 11,500 ft) and 4270 m (14,000 ft) elevation in the Front Range of the Colorado Rockies. The principal study areas were Mount Evans and Rocky Mountain National Park. These two areas are about 77 km (48 miles) apart in a north-south direction. Most of the collecting was done during 6 June 15 November 1967, but some was also done during 1966 and 1968. The 1967 frost-free season at 3750 m was 61 days long (fairly typical) with snow prevalent except in June to October. During the 1967 season pitfall trap jars, 53 mm inside diameter and 55 mm deep, were placed in the ground, their rims flush to the surface. Ethylene glycol (10 mm deep) was added as a preservative 1 Based on part of a thesis submitted in partial fulfillment of the requirements for the Ph.D. degree at the University of Colorado.