Monsoon Season

August 15, 2014 by

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Rainy season has arrived in Portal, AZ.  For those who are unfamiliar with the area, the majority of the year’s precipitation in the Chihuahuan Desert comes in July-August, also referred to as monsoon season.  Instead of the steady, prolonged rains that the word monsoon usually calls to mind, the Arizona version consists of relatively short but intense storms interspersed with periods of blue sky.  These storms also tend to be highly localized: you may watch the rain coming at you down the valley all morning, only to have it skirt around you to the west and miss you completely.  See http://www.wrh.noaa.gov/twc/monsoon/monsoon_NA.php for more information on the North American Monsoon. 

So far this year the Portal experimental site seems to be sustaining more hits than misses, and it’s shaping up to be a fairly “good” rainy season.  To see how the current season is measuring up to recent years, I’ve plotted total monthly precipitation through time in the figure below, with monsoon seasons highlighted as grey bands.  July 2014 was the 5th rainiest month in the past 14 years, exceeded only by the rainy seasons of 2004, 2006, 2008, and 2011.  And we still have August to look forward to! 

Time series of precipitation at Portal

Time series of precipitation at Portal

So what will this mean for our study?  One may predict that a pulse of precipitation in a moisture-poor ecosystem should cause an increase in plant growth.  Indeed, we have found evidence that the rainy season is correlated to a peak in vegetation, and that more precipitation generally means higher peaks. The following plot shows this (approximately) linear relationship between summer precipitation and summer vegetation.  The astute observer may notice that 2002 and 2007 managed to reach high levels of plant activity with low levels of precipitation.  I would first like to note that the site’s weather station was not operational during 2002 and so precipitation during this time was estimated using data from a nearby weather station which, due to the patchiness of storms mentioned above, may not be a valid estimation.  For 2007 I have no such excuse; either there are anomalies in the vegetation dataset I’m using (which is satellite-derived Normalized Difference Vegetation Index), or the rain-plant relationship is somewhat more complicated than I’ve assumed.  For the present season, if it keeps raining at the same rate we’ve seen so far, we will get about 180mm in total, putting my prediction of vegetation index at 0.42-0.43.  We’ll see how this pans out in another month or two. 

Precipitation vs. Vegetation linear regression

Precipitation vs. Vegetation linear regression

The response of the rodent community to rainy season is much more difficult to observe than the plant response.  The plant activity inspired by rainy season provides a surplus of food to the rodents, which encourages reproduction and should result in an increase in rodent abundance.  However, current research suggests that short-term weather events have little to do with rodent population dynamics, that models must incorporate weather patterns from the past year or more to detect subsequent changes in rodent abundance.  For example, numbers are not likely to increase after a single “good” summer monsoon, but they may if the site experiences a wet winter followed by a wet summer or two wet summers in a row. 

Researcher and researchee enduring inclement weather

Researcher and researchee enduring inclement weather

I want to conclude by thanking local contractor Bob Walton for the beautiful new roof on our ramada.  Just in time to keep our heads dry during this past sampling weekend! 

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Spring 2014 Plant Census

April 23, 2014 by

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Last month brought members of the weecology group (Dr. Morgan Ernest, recent graduates Dr. Glenda Yenni and Dr. Sarah Supp, and current graduate student Erica Christensen) back to Portal for the (approximately) semi-annual plant census.  Winter rains had provided us with a decent selection of annual plants to count and identify, which was a welcome contrast to the sparse plant census in spring 2013.  The breakout stars this year were smallflowered milkvetch (Astragalus nuttallianus), which showed up hundreds-strong in some quadrats, Esteve’s pincushion (Chaenactis stevioides), and the invasive redstem stork’s bill (Erodium cicutarium).  One of the most striking desert flowers found in the area, the California poppy (Eschscholzia  californica Mexicana), was also present on many plots.

Eschscholzia  californica Mexicana

Eschscholzia californica Mexicana

In total, we identified 28 annual plant species, a marked improvement from the 16 species recorded in the spring census of 2013 and quite similar to the 30 species recorded in 2012.  However while species composition was similar in years 2012 and 2014, plant abundances were much lower in 2014.  This is likely due in part to differences in total winter precipitation; precipitation was high in 2012, very low in 2013, and somewhere in the middle in 2014.

Abundances of the top 10 species for the past 3 years: Astragalus nuttallianus, Erodium cicutarium, Chaenactis stevioides, Lesquerella gordoni, Descurainia pinnata, Phacelia arizonica, Linanthus bigelovii, Eschscholzia californica mexicana, Eriastrum diffusum, Lepidium lasiocarpum

Abundances of the top 10 species for the past 3 years: Astragalus nuttallianus, Erodium cicutarium, Chaenactis stevioides, Lesquerella gordoni, Descurainia pinnata, Phacelia arizonica, Linanthus bigelovii, Eschscholzia californica mexicana, Eriastrum diffusum, Lepidium lasiocarpum

We also used the trip to perform some much-needed maintenance on the site.  The low fences around each of our 24 experimental plots require frequent upkeep to prevent the rodents from tunneling under or climbing over them, but there is also a barbed wire cattle fence around the perimeter of the 20 ha site that has gotten very little care in the past decade or so.  It only came to my attention in March, when I was surprised to find a very large herbivore chewing his cud on my study site.  We were able to chase him off with minimal damage (either physical or emotional) to man and beast, but the experience inspired me to request the help of my PhD adviser in repairing some conspicuous holes in the perimeter fence.  So how many PhDs does it take to mend a barbed wire fence?  Turns out one and a half will get it done.

Dr. Morgan Ernest deftly handling some baling wire for fence repair

Dr. Morgan Ernest deftly handling some baling wire for fence repair

The cow wasn’t the only unexpected herbivore we encountered during the March rodent census.  Caught in one of the traps, seen for the first time on the site since 2009, was a tawny-bellied cotton rat (Sigmodon fulviventer).  Three species of cotton rat have been recorded at the site (S. fulviventer, S. hispidus, and S. ochrognathus), all of which prefer grass-dominated habitat to shrub-dominated.  They have been uncommon but persistent at Portal since its inception in 1977, and were even fairly abundant when the area was dominated by lush grasses in the mid to late 2000s.  However recent years have seen decreased rainfall and therefore the plots have been more characteristic of shrubland than grassland, and the Sigmodons moved elsewhere.  Does the return of the cotton rat mean a return to grassland is on the horizon?

S. fulviventer wasn't as excited to see me as I was to see him

S. fulviventer wasn’t as excited to see me as I was to see him

The Portal Project Phase 2: Coming Soon

March 18, 2014 by
Winter annuals from 2012(?). Beautiful blooms like this seem to be an increasingly rare sight!

Winter annuals from 2012(?). Beautiful blooms like this seem to be an increasingly rare sight!

Stay tuned. The Portal Project blog is coming back on line with new material and new contributors! We’ve been busy at the site with some cool results and a new grant to fund new directions. We’ll start posting about it all soon. For those of you who follow this blog, previous contributors Sarah Supp and Glenda Yenni have both graduated, though they are both still working on Portal projects and come back to the site from time to time! Erica Christensen has taken their place and plans to post regularly about what’s going on at the site. In the meantime, let this beautiful picture by Glenda in the Portal archives suffice until we finish writing up some new material for the blog!

 

What’s going on outside the Portal site?

December 7, 2012 by

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?

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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.

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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!

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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 by

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.

Coatis and programmers in the desert

September 25, 2012 by

An update from the May Portal trip (which occurred immediately after my Giant Kangaroo Rat foray):

Recent USU graduate, Ben Morris, who had been working with the Weecology lab for the past few years, finally made it out to our field site, just before starting his Ph.D. with the Hurlbert lab at UNC! Ben spends most of his time on the computer being a ninja at utilizing ecoinformatics and big data, but he proved quite worthy in the field. We also saw a coati in the middle of the desert. Not sure what it was doing out there, but it didn’t look too happy… (sorry, no coati pictures to prove it!)

Ben and onychomys

Ben weighs a grasshopper mouse.

Ben measures the hind foot length of a kangaroo rat.

Portal Squee: Nesting Cactus Mice

September 25, 2012 by

This post is way overdue, but the photos are so cute that I couldn’t help myself. Back in March 2012, when Glenda Yenni, Xiao Xiao and I travelled to Portal to count the winter plants, we discovered cactus mice (Peromyscus eremicus) nesting in a box that we were using to hold firewood. When we took the wood out of the box, there was a flurry of activity and a big fluffy nest inside!

Peromyscus eremicus in a box

A scared cactus mouse runs around the box.

What was even more interesting was that the nest had a two (eartagged!) adults  pair with 2 different ages of offspring! There were 3-4 subadult mice along with 2-4 teeny tiny juveniles (it was hard to count in the dark with all the running around). The juveniles were small enough (although they did have hair) that they remained attached to the nesting female when she ran out of the nest.

I mentioned this to Karen Mabry, who sometimes helps out at Portal, and she suggested that although not much seems to be known about Peromyscus eremicus, they may be “more monagamous” than some other species mice. Some other Peromyscus species are known to be socially and genetically monogamous, and have sometimes been confirmed as nesting with sisters (rather than a male-female pair), which could potentially explain why there were 2 different ages of juveniles in the nest box.

Peromyscus eremicus in nest

Female cactus mouse peers out of nest.

(Photo credits: Glenda Yenni)

Adventures with Giant Kangaroo Rats

June 25, 2012 by

No, there are no Giant Kangaroo Rats at Portal – but there are a few pockets where they occur in California. In late May, I travelled to the Carrizo Plain National Monument with graduate researcher Tim Bean (who visited the Portal site in December 2011) to work on his project with Giant Kangaroo Rats (GKR; Dipodomys ingens). Tim is studying the relationship between habitat quality and species distribution models and has 8 trapping grids located throughout the Monument in locations predicted to be great for GKR and poor for GKR.

CPNM

This area of Carrizo is probably more like the historic landscape. Here we captured 3 species of Kangaroo Rat: Giant, Short-nosed, and Heerman’s.

Carrizo itself is the largest remaining “intact” piece of San Joaquin Valley desert-grassland; most of the valley was converted to agriculture in 20th century. Carrizo escaped irrigation because of it’s higher elevation, out of the Central Valley. It’s home to a suite of threatened & endangered species, such as the San Joaquin Kit Fox, Blunt Nosed Leopard Lizard, San Joaquin Antelope Squirrel and a suite of unique plant species.

GKR is the largest species of Dipodomys and is federally and state endangered due to extreme habitat loss. It is estimated that the population in Carrizo Plains NM was down to a few hundred in the early 1980s, but is now estimated to be somewhere in the tens to hundreds of thousands – so it appears the GKR story may have a happy ending. There are a few other remnant populations of GKR, but Carrizo is (by far!) the largest of them.

Here I’m holding a Giant Kangaroo Rat for scale – watch out! They scratch with their sharp little claws! Also, note the awesome field biologist vest.

A close up of a Giant Kangaroo Rat.

brome grass hay piles

GKR make large ‘hay piles’ of brome grass seeds on top of their mounds. It is unknown if the seeds remain in these ‘open’ caches, or if they are later removed to a burrow or pit cache.

Because of their sensitive status and relatively high capture rates, we conducted the field work all night, in the dark. Carrizo NM gets quite hot during the day, and we didn’t want to risk killing any rodents in heated up metal Sherman traps (extra-long). In most of Tim’s trapping grids, we only captured GKR (and a few late-evening antelope ground squirrels). At a few sites, however, that seem to represent more undisturbed Carrizo Plain habitat, we also captured Short-nosed Kangaroo Rats (Dipodomys nitratoides) and Heerman’s Kangaroo Rats (Dipodomys heermani) (both still larger than the Merriam’s and Ord’s we capture at Portal; 80-100 grams).

A Short-nosed Kangaroo Rat.

At the sites predicted to be poor GKR habitat, we mostly captured small pocket mice such as the California Pocket Mouse (Chaetodipus californicus) and the San Joaquin Pocket Mouse (Perognathus inornatus).

San Joaquin Pocket Mouse – it’s cute and orangey! A weird side note is that they smell kind of sweet, like kettle corn… CAUTION: Don’t try this at home. In order to avoid disease, you should never sniff dusty rodents or any dusty place they may have defecated.

A juvenile California Pocket Mouse at a “poor” GKR trapping site.

California Pocket Mice have stiff, white, spiny hairs on their rears.

Through the (desert) looking-glass

May 17, 2012 by

Between the March and April Portal trips, I fell through the looking-glass into the Namib Desert. Everything there felt so eerily similar to southeastern Arizona, yet also strikingly different. Compare the below photos from the Spitzkoppe, a large granite massif of volcanic origins in the western Namibian Desert, and of Portal (the Chircahuan mountains also are eroded granitic domes with volcanic origins!).

Spitzkoppe, the “Matterhorn of Namibia”

Chiricahua Mountains, with the Portal Project in the foreground, October 2007

Although I didn’t actually get to see or handle any small mammals while visiting the Spitzkoppe, there are diverse rodent communities in the Namib desert, as there are in southeastern Arizona.

Unidentified small mammal hole, Spitzkoppe.

Banner-tailed kangaroo rat (Dipodomys spectabilis) hole, Portal.

Both Portal and the Spitzkoppe are arid grassland deserts on the edge of small, isolated mountains. Both have acacia shrubs with white thorns, and both abound with spiny and woolly vegetation. However, Namibian shrubs are inhabited by weaver bird nests rather than cactus wren nests (but both are roundish with small, circular openings).

Weaver bird nests in an acacia, Spitzkoppe.

Cactus wren nest in a cholla, Portal July 2009

The large, eroded granite rocks are similarly enticing, easy to climb and explore, and also host populations of small cryptic scorpions, spiders, rodents, and lizards, although in Namibia, unlike Portal, you are likely to see groups of hyraxes. The surrounding plains are home to a variety of antelope and grazers (such as springbok, hartebeest, zebra, warthog and rhino, to name a few) rather than Coues white-tailed deer or javelina.

A very cryptic Agamid lizard, Spitzkoppe

Texas Horned Lizard, Portal (Photo courtesy of R.P. O’Donnell, May 2011)

Hyraxes are NOT large rodents, but are actually more closely related to elephants! These are Rock Hyraxes (Procavia capensis).

Euphorbia virosa, “poison tree”, in the Spitzkoppe. Although it looks similar to organ pipe cactus, this is NOT a cactus, but a member of the spurge family.

Experiencing another, similar desert was an amazing experience which I hope to repeat, but I eventually crossed back to my hemisphere and the right side of the looking-glass, where my world was again familiar and the research at Portal was waiting for me to return…In late April, we captured our first pack rat (Neotoma albigula) since Fall 2009 !

Neotoma albigula

Sarah documenting the Return of the Pack Rat.

There was no rain between March and April, so the vegetation was all going to seed and the soil was dry and dusty again. Rodent abundance and diversity continues to rise, however, so they must be caching all those valuable little seeds!

Nic Kooyers, a graduate student at Washington University in St. Louis, came to learn about the project and look for unique desert vegetation. Nic is especially interested in the evolution of plants that display variation in the production of secondary compounds, but he really liked the rodents, too.

NKooyers_krat

Nic weighing an Ord’s Kangaroo Rat (Dipodomys ordii).

 

14,380

April 19, 2012 by

The intrepid Portal adventurers counted 14,380 individual plants on 382 sampling quadrats (0.25 m2 each), while also trapping >150 rodents, in only 4 days (March 12-15)! It was a whirlwind trip, but we had a lot of fun and learned a lot about plants! The numbers show Astragalus nuttalianus (Nuttall’s milk vetch, a very small plant) and Erodium cicutarium (Stork’s Bill, a dominant, spreading rosette) to be the most common annuals by far, followed by Lesquerella gordoni (Gordon’s Bladderpod, with pretty yellow flowers), Chaenactis steviodes (Esteve’s pincushion, a fleshy plant with white flowers), and Descurainia pinnata (western tansy mustard, a leggy, inconspicuous mustard).

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