Updated 14 May 1997
Hear the Big Thicket (17 Feb 95)
| Funded by TNC Texas in 1995, 1996, 1997 |
| Thanks TNC ! |
Background: We are evaluating the potential of using
aquatic insects as biological indicators of ecosystem integrity
in the Sandylands: Roy E. Larsen Sanctuary. Different aquatic insect
species have different ecological requirements (food, dissolved
oxygen, pH, temperature, etc.) that must be met in order to complete
their life cycles. If the fundamental ecological requirements
of a particular insect species are not met, if even for a short
time (such as a period of low dissolved oxygen), that species
will be eliminated from the insect assemblage. Since aquatic insects
must remain in wetlands, streams and rivers during early development
stages, they act as integrative biological indicators; if a particular
insect species is present, its ecological requirements must have
been met during the time period that it took for that insect to
complete the aquatic phase of its life cycle. Aquatic insects
are not directly managed by nature preserve managers; however,
certain management practices (such as burning or vegetation removal)
can be evaluated for these non-target organisms since these practices
may affect aquatic insect habitat.
Study Objectives: Our study has four objectives;
1) to inventory positively phototaxic (move towards light) insect
orders at the Roy E. Larsen Sandyland Sanctuary, 2) to determine
if baygalls, riparian areas and ponds can be distinguished from
each other using representative insect orders, 3) to determine
if these three areas have characteristic caddisfly assemblages
that can be used as a 'biological targets' to evaluate and monitor
environmental manipulations, and 4) to determine how prescribed
burning may affect insect communities. We proposed to sample and
analyze wetland insect populations before and after burning and
during four separate three-day periods in 1995.
Ten sites were visited within the Sandylands Nature Preserve on seven dates ( 16-19 February, 18 April, 2-4 June) in 1995. Five of the sites were wetland, river or pond sites and the remaining five sites were upland sites. Not all sites were sampled during each trapping event. Light traps were run from dusk to dawn and resulted in the capture of more than 51,000 individual insects belonging to 16 orders. Overall, Diptera was the most commonly collected order accounting for more than 46% of the total number of individuals. The second most commonly collected order was Coleoptera which accounted for 23% of the total number of individules. Interestingly, the wholly aquatic orders, Trichoptera, Ephemeroptera and Plecoptera collectively accounted for less than 4% of the total number of individuals collected.
A t-test was made in order to determine if there was a statistically significant difference in the number of individuals in wetland and upland sites. There was no significant difference.
In order to determine if there was a statistically significant difference between wetland and upland sites, a t-test was performed. In this case, there was a statistically significant (P > 0.01) difference in the number of orders at wetland and upland sites.
When light trapping results from the wet sites were compared to the upland sites, Diptera and Coleoptera were the orders with the most individuals represented and the percentage of the total number of individuals were just about the same . The Trichoptera are more important (as indicated by proportion of individuals) at wet sites than at upland sites. This suggest that Trichoptera may be important in distinguising between upland and wetland sites.
Five families belonging to the Order Trichoptera have been observed at Sandylands: Hydropsychidae, Hydroptilidae, Leptoceridae, Polycentropodidae, and Psychomiidae.
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