Beetles In The Bush

Cicindela willistoni estancia. Photo by David Melius.

The latest issue of CICINDELA (December 2009, vol. 41, no. 4) contains an interesting paper by David A. Melius titled, “Post-monsoonal Cicindela of the Laguna del Perro region of New Mexico.” This paper continues a theme that I have touched on a few times in recent posts regarding the partioning of resources by multiple species of tiger beetles utilzing the same habitat. The author reports on the results of two visits to the Laguna del Perro salt lake region of New Mexico (Torrance County) in July 2009, during which time he recorded a total of eight tiger beetle species in the area. As in many other parts of the arid west, tiger beetles in this region are highly dependent upon summer monsoonal rains to trigger adult emergence (Pearson et al. 2006), resulting in multiple species occupying a given habitat during the relatively short post-monsoonal period. However, according to the competitive exclusion principle (Hardin 1960), two species cannot stably coexist in the same habitat and compete for the same resources—one of the two competitors will always overcome the other unless resources are partitioned to avoid competition.

Cicindela willistoni estancia. Photo by David Melius.

Tiger beetles that occupy the the same habitats employ a variety of mechanisms for avoiding direct competition. One of these is partitioning the environment into different “microhabitats.” One of the earliest reports of this was by noted American ecologist Victor Shelford, who reported that adult tiger beetles on the southern shores of Lake Michigan occupied different habitats from water’s edge to oak forest floor (Shelford 1907). Similarly, Choate (2003) found three sympatric species of tiger beetles in a coastal mudflat region in South Carolina, each of which utilized a different portion of the salt marsh. I myself have noted multiple species occupying the same habitat in Oklahoma’s Salt Plains National Wildlife Refuge, on a coastal salt marsh in Florida, and in the White River Hills of southwestern Missouri.

In the present study, the author noted distinct preferences among the eight species for different microhabitats within and adjacent to the salt flats, including 1) thick, wet mud immediately adjacent to the water, 2) damp, soft sand 10-20 m from the water and devoid of vegetation, and 3) dry to damp sand further away from the water with salt-tolerant plants. Nearby roadside habitats were also noted as an additional microhabitat. The species found and their preferred niches were:

• Cicindela fulgida rumppii, exclusively in vegetated dry sand areas around the salt flats.
• Cicindela (Cicindelidia) nigrocoerulea, mostly 10-20m from the water’s edge, a few also in roadside habitat.
• Cicindela (Cicindelidia) punctulata chihuahuae, exclusively in roadside habitats.
• Cicindela (Cicindelidia) willistoni estancia, mostly along the water’s edge.
• Cylindera terricola cinctipennis, exclusively in dry grassy areas away from the water.
• Ellipsoptera nevadica, exclusively along the water’s edge.
• Eunota togata fascinans, unvegetated areas near and 10-20m from the water’s edge.
• Habroscelimorpha circumpicta johnsoni, limited to roadside habitats and vegetated dry sand areas around the salt flats.

These microhabitat partitions can be visualized below. Note that although eight total species were collected, only 2-4 occur within each particular microhabitat and that all eight species were limited to just 1 or 2 microhabitats, resulting in unique species-guilds for each.

Some differences were also noted in species present during the different trips, suggesting that species occurring within the same microhabitat are also utilizing differences in temporal occurrence to further minimize competition. Differences in size among the different species were noted as well – for example, of the four species occurring in the vegetated, dry-damp sand microhabitat, Cylindera terricola is notably smaller and Habroscelimorpha circumpicta notably larger than the others. Since mandible length of adult tiger beetles is highly correlated with preferred prey size (Pearson et al. 2006), this likely results in utilization of different prey, further partioning resources within the different microhabitats.

I thank David A. Melius (Albequerque, New Mexico) for allowing me to include his stunning photographs of Cicindela willistoni estancia in this post.

REFERENCES:

Choate, P. M., Jr. 2003. A Field Guide and Identification Manual for Florida and Eastern U.S. Tiger Beetles.  University Press of Florida, Gainesville, 224 pp.

Hardin, G. 1960. The competitive exclusion Principle. Science 131:1292-1297.

Melius, D. A. 2009. Post-monsoonal Cicindela of the Laguna del Perro region of New Mexico. CICINDELA 41(4):81-89.

Pearson, D. L., C. B. Knisley and C. J. Kazilek. 2006. A Field Guide to the Tiger Beetles of the United States and Canada. Oxford University Press, New York, 227 pp.

Shelford, V. E. 1907. Preliminary note on the distribution of tiger beetles (Cicindela) and its relation to plant succession. Biological Bulletin of the Marine Biological Laboratory at Woods Hole 14:9-14.

Copyright © Ted C. MacRae 2009

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