Monday, August 1, 2011

A Declining T&T Herpetofauna?

The advantage of field notes over time is that they allow you to compare data from year to year. Recently I realized that I had the data to compare the Trinidad and Tobago herpetofauna from 1982, 1983, 1984, 2010, and 2011. The number of species I had seen on each of these trips at the same time of years for approximately the amount of time. So, I scoured my notes and built a table that compares the number of species of frogs, lizards and snakes I had seen on each of five trips. The trips were all made during June-July, the rainy season and lasted 3 to 4 weeks. At the end of each day I always tried to write a list of the species I had seen, a practice that I had started on the first trip. So, totaling the species seen on each trip was relatively easy, assuming omissions are about equal for each year. While I would often note seeing or hearing a particular species of frog I did not keep tract of the number of individuals of each species. The same was true for lizards - not wanting to count the ubiquitous Gonatodes vittatus or Ameiva ameiva. Snakes on the other hand are a different story. I did try to keep tract of the number of individual snakes seen on each trip - so they provide another aspect of the herpetofauna at two points in time (the early 1980s and the early 2010's). Table 1. shows the number of species of each higher category seen on each trip. Table 2 shows the number of individual snakes seen on each trip. One could argue that the declining numbers reflects a change in effort - afterall I am 30 years older. However, on each trip I had people assisting me, in the case of the most recent two trips we had The Glasgow Zoological Society Expedition (more than 12 people each year) looking for snakes which substantially increased the effort over the the 3 or 4 people who were with me on the 1980 trips. In the early 1980's many of the specimens recorded were road kills, in the two most recent trips road killed were exceptionally uncommon. There was a large DOR Pseudoboa on Tobago and a DOR Epicrates maurus on Trinidad in 2011 - finding only two road killed snakes in four weeks is not reassuring. Looking at my field notes it was not uncommon to find three to five road kills per night in the 1980's. 


Table 1. Number of species observed each year.

1982
1983
1984
2010
2011
Frogs
21
13
21
15
17
Lizards
10
11
13
13
14
Snakes
20
24
20
5
10
Totals
61
48
54
33
41



Table 2. Number of snake specimens observed each year.

1982
1983
1984
2010
2011
Snakes
63
57
40
8
28


1 comment:

  1. I countenance, I make not been on this webpage in a endless time? withal it was added feeling to see It is such an vital content and ignored by so numerous, alter professionals. I thank you to service making grouping more alive of practical issueExcellent บาคาร่าออนไลน์ whatsis as exemplary.

    ReplyDelete