mountainbreakfast

Introduction and site description:     Butterfly surveys have been used around the world for several decades to determine the ecological health of habitats and to document or measure changes over time. In El Paso County, since F. Martin Brown began his first forays into the hills to document butterfly ranges in the 1930’s, the human population has grown from about 33,000 to over 587,000. In the same time interval, the land area of Colorado Springs proper has increased from about 12 square miles to nearly 300 square miles, and the current human population density of Colorado Springs is about 2027/square mile, and that of El Paso County about 276/sq. mi. (http://www.citydata.com/county/El_Paso_ County-CO.html; U. S. Census Bureau 2000 Report). Although the habitat loss concomitant with development caused many local population extinctions, especially as wetlands were disturbed, the city of Colorado Springs today is bordered by abundant preserved public lands, and it is probable that most butterfly populations in the areas around the city are little changed in the wake of this extensive development. Strongly restricted species, however, may now have fewer refugia and may occur in depressed populations. Regional extinctions may have gone undetected. Continue reading “Butterfly abundance indices, Bear Creek Canyon, El Paso Co., Colorado”

Obviously, it’s not spring yet, but with the last few warm days, the butterfly species that hibernate as adults (most butterflies hibernate as pupae, larvae or even eggs) are feeling springtime in the air. Today in Bear Creek I found two species, the earliest date ever for the anglewing, and the second earliest date for the mourning cloak (Eric Eaton saw a mourning cloak in town on the 6th!). These species emerge from the pupa in August, September, October or even November, and then find safe refuge in deep grass clumps or under bark until spring. But 75°F feels a lot like spring to us, and to butterflies as well. the top is the mourning cloak (Nymphalis antiopa) and the bottom the zephyr anglewing (Polygonia zephyrus).

My goodness, I’ve been going back through my old data sets from the 2006 and 2007 season when we studied the effects of forest thinning on many aspects of the ecology, including the invertebrates, which, to me, suggests moths. Look at these graphs, for example. Each of them considers a single group, or genus, of moths as they respond to thinning across the years. The leftmost points are from the control stand–never thinned. The next point, moving right, is a collection made from a stand thinned the previous year. The highest points are collections made four years after the thinning. And the last point, way off to the right, is a collection made sixteen years after thinning. Look at the pattern.

Can you see the trend in all of these groups? The upshot is that they all show reduced numbers after one year of thinning, then they all show increasing numbers after four years. Then, by sixteen years after thinning, the numbers fall to near the original set. The bottom graph shows the overall biodiversity of ALL moths in this study. But the wonder of wonders is that, while the biodiversity is about the same after sixteen years, the community has greatly changed. That is, many of the original species are gone, but have been replaced by a new set. So biodiversity is not affected, but the community structure is very, very different. All this to be published in the next year. One of my 2017 goals. Questions? Ask.

Do you have any idea how many moth species live in the Pikes Peak Region? Take a guess. A hundred? A thousand? Ten thousand? Well, it turns out, if you have data like I have, a reasonable estimate can be made. I used the Clench equation, taken from Harry K. Clench’s paper* on estimating butterfly biodiversity on reserves. It is useful after a few years (or hours) of data points are available. If you want the answer, you can skip the math and go to the case study, below. But in case you’re interested…

The equation shows that the eventual number of species (S_e) in a locality can be estimated as a function of a constant, K, and the number of hours spent in the field (N).

As K approaches zero, N + K approaches N, and Se = S. In this equation, S represents the number of species taken at any given time and N represents the number of years (or hours) afield. Simplified, the equation looks like this:

 

Data that show a positive curve will not apply, of course. This can result if the first expedition is poor but the second is extraordinary. But as more data accumulate, a negative curve is generated, and any two points roughly on the curve can be used to estimate the asymptote, which is equivalent to S_e.

Let us assume that after two years, 62 species have been cataloged (2, 62), and that after an additional 2 years, a total of 81 have been recorded (4, 81). Using these to create a system of equations allows us to calculate K, and then S_e, as follows.

2S_e = (2)(62) + 62K

4S_e = (4)(81) + 81K

multiplying the first equation by –2 yields this pair:

– 4S_e = –248 – 124K

4S_e =   324 + 81K

eliminating the S_e term,

0 = 76 – 43K

– 76 = –43K

K = 1.77

Substituting into the original equation yields an estimate of

S_e = 124 + 110 = 234 species

A CASE STUDY:  MOTH BIODIVERSITY IN THE PIKES PEAK REGION

*Clench, H. K. 1979 How to make regional lists of butterflies: some thoughts. Journ. Lepid Soc 33(4) 216-231