Xanthippus Corallipes Research Articles

Short-Term Effects of a Summer Wildfire on a Desert Grassland Arthropod Community in New Mexico

Surface-active arthropods were sampled after a lightning-caused wildfire in desert grassland habitat on the Sevilleta National Wildlife Refuge, Socorro County, NM. Pitfall traps (n = 32 per treatment) were used to evaluate species-specific "activity-density" indices after the June wildfire in both burned and unburned areas. In total, 5,302 individuals were collected from 69 taxa. Herbivore activity-densities generally decreased, whereas predators often increased in the burned area; pitfall trap bias likely contributed to this latter observation. Fire caused the virtual extirpation of scaly crickets (Mogoplistidae), field crickets (Gryllidae), and camel crickets (Raphidophoridae), but recolonization began during the first postfire growing season. Several grasshoppers (Acrididae) also exhibited significant postfire declines [Ageneotettix deorum (Scudder), Eritettix simplex (Scudder), Melanoplus bowditchi Scudder, and Amphitornus coloradus (Thomas)]. Some beetles showed lower activity-density, including Pasimachus obsoletus LeConte (Carabidae) and Eleodes extricatus (Say) (Tenebrionidae). Taxa exhibiting significant postfire increases in activity-density included acridid grasshoppers (Aulocara femoratum (Scudder), Hesperotettix viridis (Thomas), Trimerotropis pallidipennis (Burmeis.), and Xanthippus corallipes Haldeman); carabid beetles (Amblycheila picolominii Reiche, Cicindela punctulata Olivier), tenebrionid beetles (Eleodes longicollis LeConte, Edrotes rotundus (Say), Glyptasida sordida (LeConte), Stenomorpha consors (Casey); the centipedes Taiyubius harrietae Chamberlin (Lithobiidae) and Scolopendra polymorpha Wood (Scolopendridae); scorpions (Vaejovis spp.; Vaejovidae); and sun spiders (Eremobates spp.; Eremobatidae). Native sand roaches (Arenivaga erratica Rehn, Eremoblata subdiaphana (Scudder); Polyphagidae) displayed no significant fire response. Overall, arthropod responses to fire in this desert grassland (with comparatively low and patchy fuel loads) were comparable to those in mesic grasslands with much higher and more continuous fuel loads.

Endophyte-grass-herbivore interactions: the case of Neotyphodium endophytes in Arizona fescue populations.

Neotyphodium endophytes in introduced agronomic grasses are well known to increase resistance to herbivores, but little is known of interactions between Neotyphodium endophytes and herbivores in native grass populations. We investigated whether endophytes mediate plant-herbivore interactions in a native grass species, Festuca arizonica in the southwestern United States, in two ways. First, to test the prediction that the presence and frequency of endophyte-infected (E+) plants should increase with increasing herbivory, we determined endophyte frequencies over a 4-year period in six natural Arizona fescue populations. We compared Neotyphodium frequency among plants growing inside and outside long-term vertebrate grazing exclosures. Second, we experimentally tested the effects of Neotyphodium infection, plant clone, and soil nutrients on plant resistance to the native grasshopper Xanthippus corallipes. Contrary to predictions based upon the hypothesis that endophytes increase herbivore resistance, levels of infection did not increase in plants subjected to grazing outside of exclosures relative to ungrazed plants within exclosures. Instead, endophyte frequencies tended to be greater inside the exclosures, where long-term vertebrate grazing was reduced. The grasshopper bioassay experiment corroborated these long-term patterns. Survival of grasshoppers did not differ between infected (E+) and uninfected (E-) plants. Instead, mean relative growth rate of grasshoppers was higher on E+ grasses than on E- ones. Growth performance of newly hatched grasshopper nymphs varied among host plant clones, although two of six clones accounted for most of this variation. Our results suggest that Neotyphodium-grass-herbivore interactions may be much more variable in natural communities than predicted by studies of agronomically important Neotyphodium-grass associations, and herbivory is not always the driving selective force in endophyte-grass ecology and evolution. Thus, alternative hypotheses are necessary to explain the wide distribution and variable frequencies of endophytes in natural plant populations.

The Effect of Standard Metabolic Rate on Egg Production in the Acridid Grasshopper,Xanthippus corallipes

SYNOPSIS. Models of energy budgets often allocate energy between the broad categories of maintenance, growth, and reproduction. An important component of maintenance costs is standard metabolic rate, which is partially determined by body temperature. The relationship between thermoregulation, standard metabolism, and egg production was investigated in adult females of the acridid grasshopper Xanthippus corallipes from six populations along an elevation gradient. Individuals thermoregulate and maintain stable afternoon body temperatures which correlate negatively with elevation. Standard metabolic rates were calculated at each population's afternoon body temperature. These rates were then used to investigate the effect of variation in standard metabolic rate on egg production. Because of the pervasive effect of mass on standard metabolic rate and egg number, the variables were log-transformed. The effect of mass was removed by regression analyses, and residuals were calculated. An analysis of the residuals revealed that intermediate values of field standard metabolic rate correlate with high egg production, suggesting stabilizing selection on standard metabolic rate.

Conservation of mass-specific metabolic rate among high- and low-elevation populations of the acridid grasshopper Xanthippus corallipes.

High-elevation populations of many grasshopper species produce small adults in response to shortened growing seasons and cooler ambient temperatures. Mass-specific metabolic rate tends to increase with elevation, and several authors have argued that this is an adaptation to accelerate development. In the present study, the relationship of thermoregulation and metabolism was investigated in adults of the acridid grasshopper Xanthippus corallipes from six populations along an elevation gradient. Thermoregulation was measured in the field, and several lines of evidence suggested that afternoon body temperatures were actively maintained within each population. Populations were found to maintain stable afternoon body temperatures that correlate negatively with elevation. Elevation had a strong negative effect on adult mass. Mass-specific metabolic rates at 35 degrees and 45 degrees C correlated positively with elevation. However, population differences in mass explained most of the variation in mass-specific metabolic rates, and when mass was used as a covariate, the effect of elevation disappeared. Mass-specific metabolic rates at afternoon field body temperatures were estimated and found not to differ among populations. Thus, differences in thermoregulation offset the effect of mass on mass-specific metabolic rate across populations, such that X. corallipes adults exhibited a common mass-specific metabolic rate in the wild, independent of large population differences in mass and ambient temperatures.

Translating across scales: Simulating species distributions as the aggregate response of individuals to heterogeneity

The mechanistic linkage between movement responses of animals to heterogeneity and distribution of populations provides a useful framework for investigating the extent to which fine-scale ecological information can be extrapolated across scales to explain broad-scale phenomena. We developed a simple, spatially explicit simulation model to explore whether patterns of species distributions across landscapes emerge as the aggregate response of individuals to fine-scale heterogeneity. As an empirical basis for this modelling exercise, we studied two species of acridid grasshoppers (Orthoptera) in the shortgrass prairie in northcentral Colorado, USA. Grasshopper distributions were sampled in two pastures that had been subjected to different intensities of cattle grazing. A large species, Xanthippus corallipes (Haldeman) was patchily distributed across this grassland, whereas the smaller Psoloessa delicatula (Scudder) occurred as a random distribution in both pastures. We produced a grid map of each pasture, in which each grid cell was classified according to 3 habitat types representing a gradient of forage abundance for grasshoppers. During model simulations, individuals were randomly distributed across the pasture maps and allowed to redistribute according to habitat-specific movement probabilities — the rate that an individual would leave a particular cell (habitat) type. Movement probabilities were extrapolated from observed movement rates of each species within habitats. We were initially unable to simulate realistic levels of aggregation for the two grasshopper species when extrapolated rates of movement were applied to the model. Species distributions thus do not emerge as a linear function of fine-scale movement rates, presumably because movement is constrained by different processes operating at different scales. Fine-scale movement responses to heterogeneity can be used to provide qualitative predictions of species' distributional patterns in different landscapes, however. For example, P. delicatula exhibited faster rates of movement through habitats comprising 92% of one pasture; such a high rate of turnover should lead to a random distribution, which is what we observed for this species in this system. Xanthippus corallipes had reduced movement in 35% of this same landscape, but was able to move rapidly across the remainder. This may enable individuals to aggregate within a minor component of the landscape and produce the clumped distributions we observed. While the general pattern of distribution can be determined from individual movement responses to heterogeneity, such information is too coarse to quantify the exact location of individuals and other statistical properties of population distributions (e.g., density).

Critical Thresholds in Species' Responses to Landscape Structure

Critical thresholds are transition ranges across which small changes in spatial pattern produce abrupt shifts in ecological responses. Habitat fragmentation provides a familiar example of a critical threshold. As the landscape becomes dissected into smaller parcels of habitat, landscape connectivity–the functional linkage among habitat patches–may suddenly become disrupted, which may have important consequences for the distribution and persistence of populations. Landscape connectivity depends not only on the abundance and spatial patterning of habitat, but also on the habitat specificity and dispersal abilities of species. Habitat specialists with limited dispersal capabilities presumably have a much lower threshold to habitat fragmentation than highly vagile species, which may perceive the landscape as functionally connected across a greater range of fragmentation severity. To determine where threshold effects in species' responses to landscape structure are likely to occur, we developed a simulation model modified from percolation theory. Our simulations predicted the distributional patterns of populations in different landscape mosaics, which we tested empirically using two grasshopper species (Orthoptera: Acrididae) that occur in the shortgrass prairie of north—central Colorado. Increasing degree of habitat specialization and dispersal range of a species enhanced the level of aggregation–the degree of clumping exhibited by the population–in our simulations. The landscape threshold at which populations became aggregated was affected by dispersal range for habitat generalists, but not for habitat specialists. Habitat specialists exhibited aggregated populations when preferred habitat occupied <40% of the landscape. Habitat generalists with good dispersal abilities occurred as aggregated populations when <35% of the landscape contained suitable habitat; habitat generalists with limited dispersal only formed patchy distributions when the preferred habitat was a minor (20%) proportion of the habitat. In field tests, a large species of grasshopper (Xanthippus corallipes Haldeman) exhibited reduced rates of travel in two microhabitats that together comprised 35% of a grassland mosaic; a smaller species (Psoloessa delicatula Scudder) had the highest residence time in a rare microhabitat that occurred in only 8% of the landscape. On the basis of our simulation results, we predicted that the large species would be patchily distributed because the abundance of its associated habitat is at the critical threshold. The small species should be unable to aggregate, given the rarity of habitat for which it has an affinity, and thus should be randomly distributed across the landscape. The distribution of these two species in this grassland mosaic matched the predictions from our simulations. By providing quantitative predictions of threshold effects, this modelling approach may prove useful in the formulation of conservation strategies and assessment of land—use changes on species' distributional patterns and persistence.

Slowed motion analysis of stridulation in the grasshopper, Xanthippus corallipes (Acrididae: Oedipodinae)

Sounds were produced by male Xanthippus corallipes (Haldeman) during courtship by rubbing a ridge on the inside of the hind femur against a linear series of nodes on a raised forewing vein. The visual component included the motion of the hind femur exhibiting its bright coral-red medial surface and the red hind tibia as a semaphore. Analysis of ultra-high-speed motion films, video tapes with synchronized oscillotrace, sonagrams, and oscillograms showed that the two femora were consistently out of phase with one another during a single up–down motion of the chirp, the signal of one modulating that of the other. The resulting sound significantly differed from that produced by only one femur. A buzz produced only by vibration (almost 70 up–down motions per second) of a single femur. Different signals may be caused also by the use of different portions of the file having different nodal densities.Xanthippus corallipes is noted for the frequent occurrence of distinctive-appearing populations. Comparison of X. c. corallipes, the subspecies used here, with a published report on X. c. pantherinus (Scudder), revealed striking differences in the color of the femoral medial surface and in signalling sequences during courtship.

Dietary overlap of grasshoppers on sandhill rangeland in northeastern Colorado.

Overlap in the diets of 14 species of grasshoppers on mixed-grass prairie in northeastern Colorado was estimated by microscopic examination of crop contents. Food availability estimates, taken by a weight-estimate method, facilitated the determination of food preferences. Two cases of high overlap in diets and period of habitat occupancy occurred between species which consumed equal or almost equal numbers of different foods (foodniche breadth) and had almost identical foraging behavior. The first case occurred early in the season between Xanthippus corallipes and Arphia conspersa with foodniche breadths of 14 and 11, respectively. The second case occurred later in the season between Amphitornus coloradus and Trachyrhachys kiowa both of which have foodniche breadths of 6. The amount of movement between plants while feeding was equal or almost equal in both cases, thus we observed high dietary overlap between species with equal ecological efficiencies. Dietary overlap between the 14 grasshopper species decreased as foodniche dimensions increased and the grasshopper population as a whole utilized each food resource approximately proportional to its relative abundance. Factors influencing the interpretation and importance of dietary overlap in this study included 1. non-synchronous life cycles, 2. seasonal changes in diets and food preferences, 3. complexity of the food resources, 4. variations in foodniche dimensions among grasshopper species, and 5. variations in diets between males and females within a species. Our findings agree with MacArthur and Levins theory that the number of competing species which can coexist is proportional to the total range of the environment divided by the niche breadth of the species.

Dietary Similarity of Some Primary Consumers

The dry—weight composition of the diets of richardson ground squirrels (Citellus richardsonii), mormon crickets (Anabrus simplex), and six species of grasshoppers (Xanthippus corallipes, Circotettix rabula, Aeropedellus clavatus, Melanoplus infantalis, Melanoplus bruneri, and Melanoplus alpinus), collected at Prairie Divide, Colorado, was determined. Many food plants were shared by these herbivores. Vetch (Astragalus spp.), sandwort (Arenaria fendleri), fungi, parry oatgrass (Danthonia parryi), bluegrass (Poa spp.), fringed sagebrush (Artemisia frigida), dandelion (Taraxacum officinale), and sedge (Carex spp.) were major foods. Bluegrasses, vetch, and sandwort would probably become limiting if population peaks of several of these herbivores coincided. The ranking of the food niches of these herbivores from specialized to generalized based on mean indices of dietary similarities is X. corallipes, A. clavatus, C. rabula, M. alpinus, A. simplex, M. bruneri, C. richardsonii, and M. infantalis. Males ate fewer species of food plants than females of the same orthopteran species, and the diets of males and females of the same orthopteran species were occasionally less similar than were the overall diets of different species on the same date.

Seasonal Dry Weight Composition in Grasshopper Diets on Colorado Herbland1

Microscopic examination of crop contents was used to determine the diet dry-weight composition and food preferences of adults of Aeropedellus clavatus (Thomas), Xanthippus corallipes Haldeman, and Circotettix rabula Relm & Hebard from a ponderosa pine bunch-grass community in northern Colorado. Grasses and sedges comprised about 97% of the diet of A. clavatus. Grasses and grasslikes comprised about 86% of the diet of X. corallipes while forbs supplied about 12%. The diet of C. rabula consisted of about 80% forbs and 14% grasses or sedges. A seasonal change in the diet and food preference occurred during the adult instar of the species studied. Insect parts and fungi were common minor constituents in the grasshopper diets.

A Two-Year Life-Cycle in Grasshoppers (Orthoptera: Acrididae) Overwintering as Eggs and Nymphs

Most grasshoppers of the prairie region of Western Canada hatch in the spring and complete their life-cycles in one year. There are a few species, however, that hatch in the fall and overwinter as partly grown nymphs; these include the oedipodines Arphia conspersa Scudd., Pardalophora apiculata (Harr.), Xanthippus corallipes latefasciatus Scudd., and Cbortophaga viridifasciata (Deg.) and the acridine Psoloessa delicatula delicatula (Scudd.). Criddle (1933) suggested this when he stated that, although the eggs of some Oedipodinae that hibernate as nymphs normally hatch within a month or two after oviposition, they occasionally fail to do so, in which case a further period of 12 months may occur before hatching takes place. The life-historia of all thest except C. viridifasciata were studied.

The Occurrence of Larvae of the Stable Fly, Muscina stabulans (Zett.) in Living Nymphs of the Grasshopper, Xanthippus corallipes pantherinus (Sc.)

The Occurrence of Larvae of the Stable Fly, Muscina stabulans (Zett.) in Living Nymphs of the Grasshopper, Xanthippus corallipes pantherinus (Sc.)