Behavioral niche partitioning in a sympatric tiger beetle assemblage and implications for the endangered Salt Creek tiger beetle

Abstract

How behavioral patterns are related to niche partitioning is an important question in understanding how closely related species within ecological communities function. Behavioral niche partitioning associated with thermoregulation is well documented in tiger beetles as a group. Co-occurring species of salt flat tiger beetles have adapted many thermoregulatory behaviors to cope with this harsh ecosystem. On first examination these beetles appear to occur in overlapping microhabitats and therefore compete for resources. To determine if behavioral niche partitioning is allowing multiple species to occur within the same harsh salt flat ecosystem we observed Cicindela nevadica lincolniana, Cicindela circumpicta, Cicindela fulgida, and Cicindela togata between 8:00 h and 21:00 h and recorded all behaviors related to thermoregulation using a digital voice recorder. Results of this study strongly indicate that competition among these species for resources has been reduced by the adaptation of different thermoregulatory behaviors such as spending time in shallow water, avoiding the sun during the hottest parts of the day, and by positioning their body against or away from the soil. The endangered C. n. lincolniana appears to rely most heavily on the shallow water of seeps for their diurnal foraging behavior (potentially limiting their foraging habitat), but with the advantage of allowing foraging during the hottest times of the day when potential competitors are less frequent. Ironically, this association also may help explain C. n. lincolniana's susceptibility to extinction: beyond the loss of saline wetlands generally, limited seeps and pools even within remaining saline habitat may represent a further habitat limitation within an already limited habitat.

Keywords: Cicindelidae; Competitive exclusion; Conservation biology; Ecophysiology; Endangered species; Thermoregulation.

Figure 1. Average salt flat temperatures by hour.

Temperatures were recorded on the salt flats where observations were made for adult tiger beetles. Temperatures were recorded one meter above the soil surface to determine ambient temperature, one cm above the soil surface to determine the air temperature the subjects were experiencing, and at the soil surface.

Figure 2. Time spent in sun or shade by tiger beetle species.

Proportion of time spent in the sun or the shade between 8:00 and 21:00 h (bars on graph) and soil surface temperature of the salt flats (dotted line) over those hours for four species of salt flat tiger beetle: (A) C. circumpicta, (B) C. n. lincolniana, (C) C. fulgida, and (D) C. togata.

Figure 3. Time spent on different substrates by tiger beetle species.

Proportion of time spent on wet soil (mud), dry soil, and in shallow water between 8:00 and 21:00 h (bars on graph) and soil surface temperature of the salt flats (dotted line) over those hours for four species of salt flat tiger beetle: (A) C. circumpicta, (A) C. n. lincolniana, (C) C. fulgida, and (D) C. togata.

Figure 4. Time spent engaging in thermoregulatory behavior.

Proportion of time spent in four distinct behaviors related to thermoregulation between 8:00 and 21:00 h (bars on graph), and soil surface temperature of the salt flats (dotted line) over those hours for four species of salt flat tiger beetle: (A) C. circumpicta, (B) C. n. lincolniana, (C) C. fulgida, and (D) C. togata.

Figure 5. Average mandible dips, wing pumps, and flight events per hour.

(A) Average recorded mandible dipping events per hour of observation for C. n. lincolniana and C. circumpicta (bars on graph), and soil surface temperature of the salt flats over those hours (dotted line); (B) Average recorded wing pumping events per hour of observation for C. n. lincolniana, C. fulgida, and C. circumpicta (bars on graph), and soil surface temperature of the salt flats (dotted line) over those hours; and (C) Average recorded flight events per hour of observation for C. n. lincolniana, C. togata, and C. circumpicta and surface temperature of the salt flats over those hours.