Revision of Portal Project - Mammals from Tue, 2010-06-22 13:24
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Overview:
The Portal Project is a long-term ecological study that has been monitoring small mammal community responses to climate and experimental manipulation of dominant rodent species since 1977 in southeastern Arizona.
Ecological Level: Community
Biome: Desert
Location: Southeastern Arizona (Lat/Long)
Spatial Scale of data: Each plot is .25 ha. There are 24 plots.
Timespan: 1977-2002
Frequency: Monthly
Observational/Experimental: Experimental (but with long-term controls).
Manipulation: Removal of kangaroo rats (Dipodomys spp.) and removal of all rodents.
Dataset Location:
Data collection summary: All plots are trapped for one night each month. Each plot consists of 49 permanent trapping locations. Around the new moon, a sherman trap is placed at each stake. Data is collected for each animal that is caught.
Data Collected: Species, gender, reproductive information, location caught, weight, hindfoot length, individual tag.
Issues:
1) "Monthly": While data collection is meant to be monthly, things happen. Trapping follows the new moon, so some years there are 13 sample periods because there were 13 new moons in a 12 month period. Weather, airline delays, etc, can cause sample periods to be missed, so some years will have less than 12 sample periods. The take home message: different years can have different sampling intensities. Do not simply sum all sample periods within a year and compare across years.
2) The reproductive status and age columns appear to be reversed, with age actually occurring after reproductive status, not before.
3) Appears to actually include data through 2006 even though the documentation indicates that the data stops at 2002.
4) There are some out of order records at the end of the file that contain a substantial number of missing values. Many of these are stake=99, indicating that the plot was trapped, but no animals were captured. However, others appear to be normal records and it is unclear if the fact that they are out of order indicates anything.