Posts Tagged ‘desert ecology’

What’s going on outside the Portal site?

December 7, 2012

The 20-hectare Portal research site has been studied for over 30 years now – and we’re still learning new things! But every additional year brings up new insights and new questions about the ecology happening in that patch of the desert. Why did certain species disappear? Where did new species come from? How important are changes in the weather to the persistence of species? Are there important trade-offs in rodent survival strategy (i.e., competition vs. dispersal)? How important are plant dynamics to rodent species composition (or vice versa)? What might we be missing by only focusing on rodents and plants?

Image

The Portal research site, and fencing around a rodent trapping plot.

One major question we’ve been thinking about more lately is the connection of the 20-hectares patch of desert that we study (Portal) to the surrounding desert. Since we know that rodents species come and go throughout the years, and they must be coming and going to somewhere else, we decided to venture outside our usual trapping grids for a few days to see what’s going on outside the Portal site.

October 12-17, a subset of the Ernest and White labs (Morgan, Glenda, Ken, Erica, and myself) travelled to do the usual monthly rodent-trapping and to trap 12 additional “outside” areas within walking distance of the site. We tried to trap in areas that might have different characteristics, because locations with different vegetation or topography could support different rodent species than we might expect at the Portal site. Our sites included two cattle tanks, some arroyos, areas grazed by cattle, and an area that used to be a study site for Peter Waser (he studies banner-tailed kangaroo rats), and has been cleared of shrubs.

Image

Cattle tanks collect rainwater, but are actually dry most of the year. This one looked like a mini-grassland.

To learn about the rodents that might occur outside of Portal, in each site we set a rodent trapping grid approximately the same size as a Portal plot (50 meters x 50 meters) and sampled the vegetation by counting the plants along an X-shaped transect. We marked our rodent trap location with pink flagging tape, which was a great idea, because otherwise it would have taken *forever* to find and pick up our traps the following morning. It turns out that walking in a straight line in the desert without a guide is really hard!Image

 

The portal crew setting out rodent traps. See the pink flagging?

We didn’t do our usual plant-survey at Portal this fall, and mid-October is a bit late in the season, but we were able to confidently identify most of what we saw, even if the plant was already going to seed. Most of the crew was new to plant transect work, but I think they were convinced that counting plants isn’t that bad, at least until we came to our final riparian area, which was full of catclaw acacia (Acacia greggii). “Cat-claw” acacia is as horrible as it sounds… like thousands of tiny, angry kittens clawing at your clothes, face, and hands. Except that these angry kittens leave the tips of their claws in your skin. Yes, we left with plenty of battle scars!

Image

The white line down the center of the photo is the transect tape for our vegetation survey. The green stuff is a thicket of cat claw acacia. Worst. Transect. Ever.

Overall, the trip was a success, and I think that everyone had a good time. Research is exciting and fun when it’s done right! I left wishing we could spend more time exploring the desert around Portal and learning more about the natural environmental gradients that might be an important part of what’s driving observations at our site. So many ecological studies are done at small spatial and temporal scales, but understanding species dynamics and connectance across a landscape is an important challenge for ecologists. Hopefully, our mini-exploration was just a first step in beginning to understand our research in the larger context of the Chihuahuan desert landscape.

September Portal update

September 30, 2012

In September, I returned to Portal bringing with me the newest Ernest lab member, Erica Christensen. It was a bit cooler than usual for mid-September, but overall, a great time of year to be in the desert. We captured 263 rodents, most of which are still represented by the desert pocket mouse (Chaetodipus penicillatus) and Merriam’s kangaroo rat (Dipodomys merriami). It’s much less buggy than other years, and it was a really pleasant weekend. No complaints about desert fieldwork in the fall!

dipodomys merriami

Merriam’s kangaroo rat.

pocket krat

A small kangaroo rat warms up in my pocket before being released. Sometimes after a cool night, rodents need a little help in the morning.

EricaCandPE

Erica helps process a cactus mouse (Peromyscus eremicus).

jumping Spider

We found this guy, jumping spider Phidippus octopunctatus, on a shrub while exploring the area surrounding the site.

zinnia grandiflora

We didn’t conduct a formal plant survey this fall due to logistical constraints, but many flowers were blooming in September. Here is a small perennial, Zinnia grandiflora.

October Rodent Census

November 7, 2011

October is one of my favorite months to be at Portal. The day and night temperatures seem perfect and the days are long enough to enjoy the scenery of the desert. Because of this, it’s also one of the best times to introduce new Portal volunteers to the site. Throughout the project’s duration, many people have come to help with the rodent and plant censuses, and many of these people have not been graduate students or even biologists. This month, I was able to bring my mom, Mary Mohlman, who works at Lincoln Elementary School in Hastings, NE. Her students have actually been studying deserts this fall, so she was excited to learn about the rodents and to take lots of pictures to show the kids.

Mary helping to set traps in the late afternoon.

Mary Mohlman getting to know a desert pocket mouse which was trapped on a total rodent exclosure plot. These individuals are set free off-site after being identified and measured.

Rodents are fun!

Our trap numbers continued to increase and we had nearly 200 individuals! In addition, some of our other species made a few cameos, including four cactus mice (Peromyscus eremicus), 4 southern grasshopper mice (Onychomys torridus), 2 silky pocket mice (Perognathus flavus), and even a new Bailey’s pocket mouse (Chaetodipus bailey)! We had one strange encounter with a very, very pregnant female kangaroo rat (Dipodomys merriami) who weighed over 60 grams (usually ~ 35-45 grams)! As soon as we let her go, she started making urgent squeaking noises and ran about 5 feet away from us towards the corner of the plot where she dug a hole, climbed inside, and covered the entrance. For the next 10 minutes, as we finished the rest of the traps on the plot, we could hear her squeaking while underground. I can’t say what was happening, but it was very strange behavior.

A new Bailey's pocket mouse. So far, its still the only one we've caught on the site in the last few months.

The rain seems to have stopped for the season and the vegetation was much drier than a few weeks ago when we completed the plant census. However, there were still plenty of very large centipedes (Scolopendra spp.) and texas horned lizards to be seen (Phrynosoma cornutum).

Eragrostis cilianensis (stinkgrass) growing along side plot 12. Winter is nearing and the vegetation will soon be gone along with many of our smaller rodent species (some of which enter torpor during the colder months).

Portal lives: a long awaited update

July 31, 2011
While I’ve been busy shirking my blogging duties over the past year, many people have been busy keeping Portal up and running. After we ran out of NSF funding last summer to fund research collection at the site, we were able to keep collecting data bi-monthly for the rest of 2010 on a shoestring budget and with a lot of help from Portal volunteers past and present. Luckily for us, rodent numbers remained extremely low throughout 2010 so maintaining rodent exclosures was not problematic, even with the decrease in trapping frequency. In addition, we were able to secure some funding for the next two years and began trapping each month again in January 2011. There is not a lot of money for incidentals, so we are continuing to use a combination of pit-tags and ear tags for individual markers until they run out and are keeping our fingers crossed that the trap shed and other necessary supplies can last a few more years.

This slideshow requires JavaScript.

Trapping this year has been interesting–dealing with record cold temperatures, smoke from the Horseshoe 2 forest fire in Cave Creek Canyon, and a very pesky pack rat that seems intent on living in our trap shed and destroying as many trap box shoulder straps as possible. The spring and winter were extremely dry, combined with record-low temperatures in February, and there was almost no spring germination. Consequently, this past winter, rodent numbers once again dropped extremely low (20-30 rodents in the entire site!), but enough survived the last year to reproduce this spring and our numbers this summer have been >100 rodents on site. This is still a very small number compared to more productive summers only a few years ago and we have also seen a drastic change in species diversity at the site compared to a few years ago. We are currently capturing only 4 species–Merriam’s kangaroo rat (Dipodomys merriami; common), Ords kangaroo rat (Dipodomys ordii; rare), desert pocket mouse (Chaetodipus penicillatus; very common), Bailey’s pocket mouse (Chaetodipus baileyi; very rare), and southern grasshopper mouse (Onychomys torridus; common). In 2011, it seems like we are drowning in desert pocket mice (Chaetodipus penicillatus). In fact, there are plots where kangaroo rats (Dipodomys spp.) should be “king” and instead, we are ONLY catching desert pocket mice! Its all very surprising, but perhaps that is what makes Portal so interesting.