Archive for July, 2016

The Banner-tailed Kangaroo Rat: The Once – but probably not future – King

July 27, 2016

In 1977 when Jim Brown, Diane Davidson, and Jim Reichman started the Portal Project, the site looked like this:

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Photo of Portal Project from around 1977 (we think).

 

This desert heaven was home to a variety of small mammals. One of the most abundant of these was the Banner-tailed Kangaroo Rat. While I feel that most small mammals are adorable (*cough* *cough* Packrat), the Banner-tail is the one that is universally beloved by generations of Portal researchers.

 

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Banner-tailed Kangaroo Rat (Dipodomys spectabilis). How can we tell? Note its size relative to the hand and the white tuft at the end of the tail.

Kangaroo rats in general are lovely creatures. As their name suggests, these nocturnal rodents hop around like kangaroos on enlarged backlegs. As least one scientist has seen a kangaroo rat use those strong back legs to leap 5 feet horizontally (with a two foot ground clearance)1. They have a long tail which may play a role in locomotion1 and fur-lined cheek pouches that they use like a bag to carry around seeds they gather from the environment. Most kangaroo rats eat primarily seeds. A study in Nevada found that Merriam’s Kangaroo Rat (a species we have at Portal) has a diet of  approximately 70-100% seeds (it varies over the year) and they eat a small number of insects as well.2 Anyway, you get the idea, kangaroo rats in general are cool. Most kangaroo rats – like Merriam’s – are about 40-70 grams (that’s about 0.09-0.15 pounds). But there are a few kangaroo rats that are notably larger. The Banner-tailed Kangaroo Rat is one of these, being closer to ¼ of a pound.

 

So, in 1977 three kangaroo rats, alike in dignity in fair Portal where we lay our scene, coexisted without evidence of ancient grudge or new mutiny4: Banner-tails (Dipodomys spectabilis), Merriam’s (Dipodomys merriami) and Ord’s (Dipodomys ordii).

The plot below shows the population dynamics of the three kangaroo rats. The plot goes from 1977 to 20145 and shows the population size in energy use6. I like energy use – especially when I’m dealing with Banner-tails – because large animals need more food than small animals. So one large banner-tail needs the equivalent amount of energy as 2¾ Merriam’s (based on their metabolic rates). By converting the population numbers to energy use, it helps correct for this difference in food consumption. So, the graph shows that early on in the study, Banner-tails were energetically more dominant than Merriam’s or Ord’s.

Kangaroo_ratplot

This is data from our long-term site. Photo credits: Merriam’s by Sarah Supp, Ord’s by Andy Teucher via ZoocodeZoo.com, Banner-tail by an unknown Portal researcher (i.e. we forgot to document who)

This all changes, though in the mid 1980s. Why? Blame Tropical Storm Octave which dumped nearly half of the annual rainfall in less than a week7. While the other kangaroo rats barely noticed this event, the Banner-tails hated it. Many individuals disappeared over the following months. The population tried to stage a comeback in the late 80s and early 90s, but like a one-hit wonder band, it fizzled. By the late 90s, the era of the Banner-tail was over. The last Banner-tail disappeared and there was much sadness among the researchers.

But you’ll notice some blips. Like a heart that beats irregularly, every few years a few little lost souls, wandering across the desert, find our site. Hopes and dreams of a new era of banner-tails spring anew only to be crushed by disappointment when once again they disappear.

Why did the Banner-tails disappear after Tropical Storm Octave and why can’t they seem to make it at our site now? It’s not entirely clear, but we think it has to do with shrubs. Banner-tails love grasslands. They don’t mind a scattered shrub here or there, but they don’t like too many shrubs 8. Sadly, since 1977, the site has become steadily shrubbier. Below are paired photos taken from approximately the same location at the site. On the left is Jim Brown on plot 4 in the late 1970s. On the right is 19959. Notice any differences? The Banner-tails definitely do!

 

All of this is ancient history. So why blog about it now? Because we are happy to report the return of the Banner-tail! Well, kind of. I mean, we currently have one lonely female – probably fairly young given her weight and state of her fur when she showed up. We’ve caught her 3 months in a row now on plot 11. The students have joked about setting up a twitter feed for her. Tweets suggested include:

“4 months since I left home. The food here is great and all the other mice are small and easy to fight off. I’m gaining lots of weight”

“Returning to my favorite bed and breakfast this weekend. Predator-free and good but monotonous breakfast. Four out of five stars”

“Young professional female spectab [shortened form of the species name of Bannertails] seeking like-minded male. Looking for something casual and fun, no relationship. Interested suitors should arrive at Plot 11”

Needless to say, we’ve been excited by the Banner-tail. Every month we’ve been wondering “Is she still here?” One day, probably soon, the answer will be no because our site is too shrubby for a Banner-tail to be happy there, but for now we dream of fields of Banner-tails.

 

 

 

  1. George Bartholomew and Herbert H Caswell. 1951. Locomotion in Kangaroo Rats and its Adaptive Significance. Journal of Mammalogy. Vol 32. Pages 155-169.
  2. Glen Bradley and Roger A. Mauer. 1971. Reproduction and Food Habits of Merriam’s Kangaroo Rat, Dipodomys merriami. Vol 52 Pages 497-507.
  3. Ana Davidson and DC Lightfoot. 2008. Burrowing rodents increase landscape heterogeneity in a desert grassland. Journal of Arid Environments. Vol 72 pages 1133-1145.
  4. How Shakespeare should have written the opening to Romeo and Juliet. (Sorry, Shakespeare).
  5. I had this data on hand and was too lazy to update with the newest data
  6. How do we figure out energy use? We estimate it from metabolic rate. There is a well known relationship between the size of an individual and its metabolic rate – larger individuals have higher metabolic rates (i.e. they require more food per unit time than smaller organisms). We used an equation for the relationship between metabolic rate and weight that was calculated for wild rodents to figure out the metabolic rate for each individual and then summed across all individuals of the species.
  7. Thomas J. Valone, James H. Brown, Carrie L. Jacobi. 1995. Catastrophic decline of a desert rodent, Dipodomys spectabilis: insights from a long-term study. Journal of Mammalogy, vol 76, pages 428-436.
  8. Peter M. Waser and James M. Ayers. 2003. Microhabitat use and population decline in Banner-tailed Kangaroo Rats. Journal of Mammalogy vol 84. Pages 1031-1043.
  9. I keep meaning to take a recent version of this, but haven’t remembered to do this when I’m at the site.
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PORTAL: The times, they are a’changin

July 14, 2016

Updates on temporal community dynamics, and a whole new project scheme.

PortalPano

Things have been quiet on the portal blog lately.

But in the lab and the field, it has been anything but.

 


Over the past year there have been big changes afoot for the Portal project.  In the summer of 2015, Weecology lab headquarters relocated from Utah State University in small, mountainous Logan to the massive University of Florida campus in subtropical Gainesville. So now we study Arizona’s desert rodents from the mossy groves of the southeast rather than the alpine forests of the Rockies, like true cosmopolitan, ever-curious ecologists.

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The Portal project headquarters relocated from Utah to Florida in summer 2015. Leaping Krat photo illustration by Molly Zisk, taken from http://www.ocregister.com

If you’re going to box up your life, you might as well reorganize it too. In the midst of planning her transcontinental move, Dr. Morgan Ernest, supported in her decision by funders at the National Science Foundation, decided it was time for a shuffle of Portal’s long-term experimental rodent community plots as well, a reorganization of the plot gates that allow some rodent species in, and keep others out. Yuri Kochiyama once said that movement is contagious. Barkpost.com said that science has finally proven that devoted dog owners often resemble their dogs. Maybe these things have nothing to do with the rigorous study of kangaroo rats in the Arizona desert. Maybe Yuri was talking about politics, not ecology and nobody actually thinks Peyton Manning looks like his dog. But maybe, when you study the ebb and flow of desert rodent populations for long enough, they have to move when you move. That’s not science. But stay tuned and we’ll tell you all about the real science of the Portal project plot move, and the people doing the moving. In the full words of Yuri, “the movement is contagious, and the people in it are the ones who pass on this spirit.”

YuriDogsActivist Yuri Kochiyama (Wikipedia.org) and people who look like their dogs (barkpost.com).
This is silliness.  Stay tuned for science.

It takes a community of people to shuffle a community of rodents, and to pass on the spirit of the Portal project.  To facilitate all this contagious movement, the Portal project lab group, like all strong biological populations, has grown in numbers over the past year. One might even call Dr. Ernest the Pied Piper of Ecology, enlisting a group of young followers in her slow migration from the mountains towards the sea. In 2015, she recruited another smammal (small mammal)-loving Portal RA, Ellen Bledsoe, to join Erica Christensen in conducting the monthly plot rodent census, officially appointed our own Glenda Yenni as Portal project manager, and brought in another graduate student, Joan Meiners, from Utah to help communicate the many exciting new projects radiating out of the Portal, Arizona site. And even though Morgan does know quite a lot about rats, we’re all pretty confident she’s not trying to drown us.

So now that we’ve gotten the debate about doppelgänger dogs, social activism, and old nursery rhymes out of the way, we can dive right in to the nitty gritty science of the new Portal project movement – what changes we made on site, and why.

Next time on this blog series, we’ll (re)begin our Portal project story in March of 2016, one year after the great plot shuffle of 2015, when this whole crew, plus two willing workers from Dr. Ethan White‘s side of Weecology, Shawn Taylor and Kristina Riemer, headed to the Arizona desert to check in on the plot switch, conduct the Portal project’s 447th rodent census and the 34th plant census (with a new high tech twist!), and dig a giant trench in a desert near-tornado.

PiedPiperThe Pied Piper, keeper of the rodent gates. http://www.mubi.com