Population Dispersion of Spider Webs

Spiders Spinnerets Webs to catch food Draglines Webs vs. Burrows Ballooning Living conditions Common Names Nesting Eggs Life cycle www.biologymad.com www.amonline.net www.ext.colostate.edu

Spider Species Sheet-web weavers Orb Weavers

Data Collection Jewell Moore Nature Reserve Random directions from central point 1 meter radius circles Limited to Forest Count # of webs in trees

Data Mean= 1.233 Variance=1.840 SD=1.357 Number of Cobwebs Frequency of cobwebs Observed P(x) Poisson 11 0.367 0.301 1 10 0.333 0.361 2 3 0.1 0.217 4 0.133 0.087 0.033 0.026 5 0.006 6 0.001 Table 1

Results In the Jewell Nature Reserve we surveyed thirty plots and found 37 spider webs, averaging 1.23 webs per plot. We expected 4 plots to contain 0 spider webs, but found 11 (see Table 1). The chi-square value, 43.28, suggests a borderline random, contagious dispersion pattern (refer to Figure 4C.6 in lab manual). Our variance to mean ratio, 1.46, is somewhat close to 1 which suggest random dispersion, but it is also above one which suggest contagious dispersion. This is consistent with our chi-square value. The number of individuals found in all the plots were close to the number of individuals predicted by Poisson which suggest random dispersion (see Table 1 and Figure 1).

Figure 1

Conclusion Why might our data be borderline between random and contagious? Old webs Different species

Conclusion Main Hypothesis: 1. The spider webs will be randomly dispersed because of food competition. Alternative Hypothesis: 2. Randomly dispersion occurs to prevent cannibalism. (see text page 253) www.amonline.com