Western North American Naturalist Volume 60 Number 1 Article 11 1-20-2000 Full Issue, Vol. 60 No. 1 Follow this and additional works at: https://scholarsarchive.byu.edu/wnan Part of the Anatomy Commons, Botany Commons, Physiology Commons, and the Zoology Commons Recommended Citation (2000) "Full Issue, Vol. 60 No. 1," Western North American Naturalist: Vol. 60 : No. 1 , Article 11. Available at: https://scholarsarchive.byu.edu/wnan/vol60/iss1/11 This Full Issue is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Western North American Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. Western North American Naturalist 60(1), © 2000, pp. 1–15 COMMUNITY STRUCTURE OF ELEODES BEETLES (COLEOPTERA: TENEBRIONIDAE) IN THE SHORTGRASS STEPPE: SCALE-DEPENDENT USES OF HETEROGENEITY Nancy E. McIntyre1 ABSTRACT.—Patterns in the community structure of darkling beetle (9 Eleodes spp., Coleoptera: Tenebrionidae) assemblages in the shortgrass steppe of north central Colorado were monitored by live pitfall trapping for 4 summers. There were significant correlations among weather (temperature and precipitation), species richness, and number of indi- viduals per species captured; effects from weather conditions also displayed 1-month and 1-yr delayed effects. Population densities of 2 eleodid species were monitored by mark-recapture methods. Densities of these species varied relatively little among years and sites, although density was correlated with temperature and precipitation. Abiotic influences on both density and richness differed between 2 macrohabitat types (shortgrass upland, shrub floodplain). The 4 largest species were most abundant in the floodplain, whereas the smallest species was most common in the upland. Affinities with cactus and shrub microhabitats (and an avoidance of bare soil) were evident, although a preference for shaded micro- habitats was not detected. These results do not conform well to previous explanations of why darkling beetle assem- blages are spatially and temporally heterogeneous, which primarily focused on predation and thermoregulation. Therefore, an alternative mechanism concerning scale-dependent uses of heterogeneity and mobility is proposed to account for eleodid community patterns. Key words: Coleoptera, community diversity, darkling beetle, Eleodes, population density, precipitation, richness, shortgrass steppe, temperature, Tenebrionidae. The shortgrass steppe of western United Upon eclosion, they may live for 2 yr as adults States is one of the least studied ecosystems in (Allsopp 1980). Adults are detritivorous, feed- North America. Disparagingly called “the Great ing mainly on grasses and forbs, and there is a American Desert” by early explorers and home- high degree of dietary overlap among species steaders because of its apparent monotony and (Yount 1971, Doyen and Tschinkel 1974, Slo- harsh climate, this biome is in fact a spatio- bodchikoff 1978, Rogers et al. 1988). Although temporally dynamic ecosystem (Knopf and flightless, the beetles are highly mobile and Samson 1997). The long-standing and persis- wander over great distances (Kramm and tent misperception of the shortgrass steppe as Kramm 1972, Calkins and Kirk 1973, Doyen homogeneous may stem from the coarse per- and Tschinkel 1974). Individuals are active ceptual scale of observers. Many of its other when temperatures permit. On the southern occupants, however, may more readily per- shortgrass steppe and in desert ecosystems, ceive the heterogeneous nature of the short- activity is usually crepuscular and nocturnal grass steppe, owing to differences in body size from spring through autumn; on the northern and mobility. In this paper I examine evidence shortgrass and mixed-grass prairies and shrub- for scale-dependent uses of heterogeneity in steppe, darkling beetles are mostly diurnal from various species of darkling beetle (Eleodes late spring through early autumn, with peaks spp., Coleoptera: Tenebrionidae) of the north- of activity in early morning and early evening ern shortgrass steppe of Colorado. (Kramm and Kramm 1972, Wise 1981b, Kenagy Darkling beetles (eleodids) are among the and Stevenson 1982, Richman et al. 1982, most abundant macroarthropods of the short- Whicker 1983, Marino 1986, Whicker and grass steppe, with as many as 9 species occur- Tracy 1987, Stapp 1997a). More detailed infor- ring in narrow sympatry (Bell 1971, Kumar et mation on darkling beetle ecology may be found al. 1976). They live most of their lives as soil- in Doyen and Tschinkel (1974), Allsopp (1980), inhabiting larvae that feed on roots and detritus. Parmenter and MacMahon (1984), Sheldon 1Department of Biology, Colorado State University, Fort Collins, CO 80523-1878. Present address: Center for Environmental Studies, Arizona State Univer- sity, Box 873211, Tempe AZ 85287-3211. 1 2 WESTERN NORTH AMERICAN NATURALIST [Volume 60 and Rogers (1984), Whicker and Tracy (1987), shaded, artificially shaded, and unshaded traps. Rogers et al. (1988), and Parmenter et al. I then tested 2 alternative hypotheses (B1 and (1989b). B2, below) regarding the relationships among The similarity of life history, diet, range, and predation risk, body size, and shrub cover. behavior among species prompts the question Although eleodids can produce unpalatable of how the darkling beetle community is quinones when threatened with predation structured in space and time. Factors that (Tschinkel 1975a), they are sometimes preyed account for spatio-temporal patterns of dark- upon by birds and rodents (Wiens et al. 1974, ling beetle community composition have been Wiens and Rotenberry 1979, Stapp 1997b). If subject to much speculation by past researchers. eleodids partition habitat according to risk of A high degree of niche overlap suggests that predation, then that partitioning may take 1 of environmental factors may play more impor- 2 forms as related to body size: tant roles in structuring eleodid assemblages and populations than do biotic factors such as (B1) Larger species, being more obvious to ver- competition and predation (Wiens and Roten- tebrate predators, should be more abundant berry 1979, Wise 1981a; but see Abrams 1980), in areas with greater shrub coverage because which may play only minor roles in determin- shrubs serve as refugia from predators; ing the abundance and distribution of darkling smaller eleodids, being less vulnerable to beetles (Wise 1981a, 1985, Parmenter and predation because of their more inconspicu- MacMahon 1988). ous size, should be widespread. Previous studies have demonstrated that (B2) Smaller species should be more abundant in darkling beetle activity and occurrence are areas with numerous refugia from predators (i.e., areas with finely textured clays with influenced by various environmental factors, cracks that serve as refugia; such soils do not including soil texture (Calkins and Kirk 1975, support high densities of shrubs); larger Krasnov and Shenbrot 1996, 1997, Stapp 1997a), species, being less vulnerable to predation abundance of food resources (McIntyre 1997), because of their size (being unmanageably shrub cover (Parmenter et al. 1989b, McIntyre large for a predatory rodent or bird), should 1997, Stapp 1997a), and thermoregulatory be widespread (Stapp 1997a, 1997b). resources (Rickard 1971, Slobodchikoff 1983, Whicker 1983, Whicker and Tracy 1987, Par- To test these hypotheses, I compared the pres- menter et al. 1989c). However, none of these ence and abundance of eleodids that differ in studies examined the interaction between abi- body size in areas differing in amount of shrub otic (weather) and environmental factors in cover. influencing eleodid communities and popu- Eleodid species exhibit different prefer- lations. In this study, I investigated habitat ences in ambient temperatures in which they occupancy at 2 spatial scales and variations in are active, perhaps reflecting species-specific eleodid density and diversity over a 4-yr period. differences in ability to conserve water (Kramm In particular, I focused on how eleodids re- and Kramm 1972, Campbell and Smith 1975, spond to temperature, precipitation, and the Slobodchikoff 1983, Whicker 1983, Whicker presence of shrubs. and Tracy 1987, Parmenter et al. 1989c). I Some eleodid species are more abundant in therefore examined 2 hypotheses of how eleo- and move to areas with greater shrub cover did richness and abundance might vary with (Parmenter and MacMahon 1988, McIntyre temperature and precipitation. Because tem- 1997), possibly because shrubs provide pro- perature and precipitation are negatively cor- tection from vertebrate predators (Parmenter related variables, these hypotheses combine and MacMahon 1988, Stapp 1997b) as well as both temperature and precipitation rather shade. I investigated both factors. than test each variable singly: Hypotheses (C1) If eleodids are heat sensitive, they should First, I tested the hypothesis (A1) that eleo- vary negatively with temperature and posi- dids prefer shrub-dominated areas because of tively with precipitation. thermoregulatory resources that shrubs pro- (C2) If eleodids are cold sensitive, they should vide. This hypothesis was addressed by com- vary positively with temperature and nega- paring pitfall-trap captures among naturally tively with precipitation. 2000] ELEODES COMMUNITY STRUCTURE 3 Inasmuch as the shortgrass