Oases From Bare Rock – The Hanging Gardens of the Southwest United States

•January 3, 2013 • 4 Comments
A terrace hanging garden in Zion National Park

A hanging garden in Zion National Park

Imagine you are walking through an arid desert region, in the height of summer. There are canyons and rock formations of soaring sandstone all around you. The vegetation is dry and scrubby, designed to withstand long periods of drought. The stream beds around you are dry and will remain that way until winter or spring. It’s a beautiful but extremely harsh environment. Suddenly, your trail turns a corner and before you is a patch of lush green vegetation – ferns and grasses and flowers and algae – growing seemingly straight out of the rock, some even upside down. As you approach you see that that the area is cool and damp and shady, with water coming seemingly out of nowhere and disappearing in a dwindling trickle below. It is the complete opposite of the habitat surrounding it in nearly every way, and by all logic, shouldn’t exist.

You’ve just encountered a hanging garden, a peculiar plant community found in the greater Colorado Plateau. Hanging gardens, at their most basic, are places where water seeps out of bare rock, often year round, in an otherwise desert environment and allows water-loving plants to thrive in places where they would otherwise never be able to grow. Not only are they lovely oases, but they are often important resources for the communities around them, and a refuge for rare and endemic species.

First thing first: How and why does a hanging garden form? Let’s start with the seep. In the areas which hanging gardens are found, the geology consists of layers of highly porous sandstone (laid down in ancient, wind swept deserts) and ones of impermeable sedimentary rock which formed the bottoms of prehistoric lakes. Rivers have cut through these layers to form the deep canyons of the southwest, and it’s this particular arrangement of rock types that allows theses seeps to form.

When rain falls on bare sandstone it finds its way into the rock, both through the rock itself and through jointing in the sandstone that allows the water to make its way downward until it hits one of the impervious layers of stone. It then collects in the porous layer, as if the former lake still existed but is now underground and happens to be full of rock as well as water. But the water has to go somewhere, and following gravity it will move along the impermeable barrier until it finds a way to continue the downward journey. Sometimes it finds joints and cracks in the impervious layer and flows through these into the next layer of porous sand stone, if there is one, or into underground aquifers. But sometimes it has to move nearly horizontally, in which case it will follow any slight downward slope of the old lake bottom and any available joint system in search of a place to go.

In places where the layers have been cut through, the water often finds its exit in the wall of the canyon. These seeps can range from barely a moist patch on the rock face to an ephemeral trickle to a year-round gushing stream or pool system, sometimes flowing into an above-ground river. But if there is moisture in the desert, it will be colonized somehow, often surprisingly quickly. A true hanging garden forms when a seep comes out in a place that is shaded for enough of the day to keep the temperature cool and relatively stable throughout both the day and night.

Hanging gardens usually have very thin, poor soils, formed by natural erosion of the rock by the water and through the action of

Southern maidenhair fern (Adiantum capillus-veneris), an indicator species for hanging gardens.

Southern maidenhair fern (Adiantum capillus-veneris), an indicator species for hanging gardens.

the first species of plants to colonize the area, ones that take hold on the rock itself or on the calcareous deposits (known as tufa) that are often left on the rock by calcium-rich water. The tufa contains not just calcium but other nutrients trapped from the rainwater as it flows through the ground, and some plants can root directly in it in lieu of soil.

Hanging gardens take three distinct forms, depending on the geology around the them, the thickness of the rock layers, and the placement of the joints in the rock. The most gravity-defying are the “window blind” gardens which appear to grow directly out of a sheer rock face, when the joint between the permeable and impermeable layers of rock is flush with both layers. This type of garden, while impressive, often supports smaller and fewer species the other types. A terrace garden happens when the permeable layer has eroded further than the impermeable layer of rock, forming a shelf on which the water can collect and eventually flow over the edge, and where plants can get a foothold more easily than on a vertical face. Soil collects more easily on the ledges and so may support less acrobatic species.

Finally, the type of hanging garden that is usually richest in species an alcove garden, where the sandstone has eroded away to form an overhanging cave, usually with a pool (known as a plunge pool) at it’s base. This type of hanging garden actually has three distinct zones in which different kinds of plants may be found. The ceiling of the overhang, from which some species may grow nearly upside down, the sheer back wall, and the floor upon which soil and detritus accumulate. The ceiling may contain ferns and adventurous flowering plants, such as maidenhair fern (Adiantum spp.), monkeyflowers (Mimulus spp.) The back wall is often primarily covered in algae, although some of the ceiling species may colonize there as well. The floor will have the highest number of species, often including sedges and grasses found in regular riparian areas, columbines (Aquilegia spp.), shooting stars (Dodecatheon spp.), and even orchids (such as the helleborine orchid, Epipactus gigantea).

Aquilegia grahamii, a columbine known only from hanging gardens in three canyons of the Uinta Basin, an area with high levels of oil and drill and greatly imperiled.

Aquilegia grahamii, a columbine known only from hanging gardens in three canyons of the Uinta Basin, an area with high levels of oil drilling and greatly imperiled.

As you might imagine, the shelter provided in a hanging garden is not limited just to plants. They support rich communities of insects and other arthropods, as well as many microscopic creatures. Depending on the size and location, any number of vertebrate species may make use of the garden as well, particularly if it contains a pool of any kind. Birds, rodents, and even larger animals may drink the water, and small birds and mice may make their homes in the garden either permanently or temporarily to shelter from a drought. The seeds and vegetative parts of the plants, as well as invertebrate inhabitants can provide a food source. And amphibians make use of the pools to live and spawn in. Hanging gardens are ecosystems unto themselves, both large and tiny – some of them are big enough to support cottonwood and willow trees!

Hanging gardens don’t just contain cool looking plants, but may also shelter rare or unique endemic plants. Some of the species found there are the same as the ones found in nearby riparian or wetland areas, but others are only found in hanging gardens in the southwest, and still others are only known from a handful of hanging garden locations, often clustered close together. New species are still being regularly discovered in hanging gardens.

There may be several reasons why hanging gardens often contain rare species. One is that they are isolated from other similar plant communities and from each other, so when a relatively common wetland plant moves in to a hanging garden, it may speciate fairly quickly because it is removed from its original population and may only be able to reproduce with others in its own garden or those immediately surrounding it. In addition, hanging gardens may be refuges for species from a previous, wetter era, which have died out almost entirely as the climate turned into a desert, while just a few individuals managed to survive in hanging gardens and the seedbanks that supply them.

Jamesia americana var. zionis, a type of Cliffrose known only in Zion National Park, Utah

Jamesia americana var. zionis, a type of Cliffrose known only in Zion National Park, Utah

Given all of this, it will come as no surprise that hanging gardens are both extremely fragile and very important to the surrounding desert, as well as a vital habitat for rare species. Hanging gardens can be destroyed or damaged by natural rockfalls, floods, or storms, as well as by human trampling on delicate soil around them. In addition, their richness can be decimated by the introduction of invasive species through disturbance, and pollution from rainwater and runoff. A series of dry years can cause a seep to disappear altogether, and climate change may cause this to happen more and more often in the coming decades.

To preserve a hanging garden, you can’t just put a fence around it. You have to protect the larger ecosystem and watershed which it dwells within, which is why large scale land conservation, like The Greater Canyonlands, are vital. And even within the strict protections of the National Park System, hanging gardens can still be damaged or destroyed by outside influence, such as increasingly common bouts of extreme weather due to global climate change. And while the most abundant and well-known hanging gardens are found in protected areas like Zion National Park, Arches National Park, and Glen Canyon National Recreation Area, many are in places with no federal protection at all, and still more likely haven’t been discovered yet.

Works Consulted:

Fowler, J. F., Stanton, N. L., Hartman, R. L., & May, C. L. (1995). Level of endemism in Colorado Plateau hanging gardens. In Second Biennial Conference on Research in Colorado Plateau Transactions and Proceedings, series NPS/NRNAU/NRTP-95/11.

Harper, K. T., Sanderson, S. C., & McArthur, E. D. (2001). Quantifying plant diversity in Zion National Park, Utah. and DJ Fairbanks, compilers. Proc. Shrubland ecosystem genetics and biodiversity, Provo, UT. Ogden, UT: USDA-Forest Service Rocky Mountain Research Station, RMRS-P-21, 318-324.

Malanson, G. P. (1980). Habitat and plant distributions in hanging gardens of the Narrows, Zion National Park, Utah. Western North American Naturalist, 40(2), 178-182.

Welsh, S. L. (1989). On the distribution of Utah’s hanging gardens. Western North American Naturalist, 49(1), 1-30.

Science Book Review: A Natural History of Ferns

•December 24, 2012 • Leave a Comment

urlA Natural History of Ferns by Robbin C. Moran is a rare type of science book. It successfully walks a line between the popular science book for the layperson and the dry technical tome. The author promises us a natural history of ferns and he delivers. The book is extremely thorough and well organized, starting with basic fern biology and reproduction, then moving on classification, evolution, unusual types of ferns, and our relationship with ferns over the years, including historically and in pop culture. I’ve always liked ferns but I had no idea how much there was to know about them. Nor did I know that horsetails are actually phylogenetically ferns.

This book is very well written without shying away from technical terms or in-depth explanations. In fact, it’s all about in-depth explanations, but they are very well done and fairly easy to follow. However, this book is definitely not for the complete layperson. The author presumes at least a basic, college level knowledge of biology and some familiarity with botany. He does try to explain terms that might be unfamiliar and provides a very helpful glossary in the back, so a very determined person with no existing science background could probably figure it out, but I definitely wouldn’t recommend this as My First Fern Book (or even My First Plant Book).

What this book is excellent at is educating a person who is already a plant nerd on an area of botany that they may know little about, or introducing someone with an existing science background to botany. The progression of topics is natural, the author is entertaining and makes a few terrible plant puns, and the discussion of the science is at a reasonably high level but not so difficult that the target reader feels like they are slogging through it or preparing for an exam.

There are two other things I really appreciated about this book. First, the chapters are very short and focused on a single topic, without wandering. This made me feel like I could sit down, read a chapter, grasp a complicated concept, and then maybe come back later for more. At no point did I feel like I was being bombarded with too much information or like I couldn’t wait for a chapter to end. This format helped me retain the information more easily than if the chapters had been longer and tried to cover too many things.

Second, while the author does provide a very detailed level of information, large concepts are stressed over nitty-gritty mechanisms. The small scale stuff was there, but I felt like I could still get something out of each chapter without having to remember ever name for every structure on the fern reproductive structure, for instance. This book definitely gets my endorsement for anyone with a botanical interest who wants to go a little deeper. I would love to see more science books of this quality and level of discourse.

Lazy Saturday Links – 12/22/12

•December 22, 2012 • 1 Comment

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Happy Solstice (a day late)! I’m sure we’re all glad the days are going to start getting infinitesimally longer now. I’m having an extraordinarily lazy Saturday and that means – links! Have a great weekend, everyone!

Ecology/Evolution Links:

1: A victory for sea otters. My favorite mustelids are not only growing in numbers, but they will now have access to previous “otter free” zones, which means they can nom those sea urchins to their furry hearts’ content. Not loving the idea of de-listing them when they reach a population of a little over 3,000, though. That’s not very many, really (NY Times).

2: Sad news from the Chicago Field Museum, which will be cutting their research budget and staff. They have the one of the most extensive natural history collections in the world. A museum like this is a research institution, and it loses its purposes when it stops doing that. Not to mention the amount of knowledge and data that will be lost if the collections are allowed to deteriorate. Sarah Werning explains brilliantly (The Integrative Paleontologist).

3: A fungus has been killing thousands of frogs every year, of more than 200 species, driving some species to extinction. Scientists finally think they know the carrier – crayfish. Ed Yong explores the bizarre and problematic life cycle of this frog-killer (Not Exactly Rocket Science).

4: A tropical pitcher plant has a unique, and highly successful, way of catching its prey. We’ve already established that I love carnivorous plants, so I’m always excited to learn about a new one! (Smithsonian)

5: A stunning 126 new species have been discovered in the Mekong Basin in the last few year. A slideshow of the 12 most charismatic. And people say the world has been explored and there’s nothing new. Ha! (The Guardian).

General Science Links

1: Cold plasma? I know it exists, but still can’t quite wrap my brain around it. Jen Ouellette takes us through this strange type of matter and its many uses. But can I play with it? (Cocktail Party Physics)

2: A rundown of the top scientific discoveries of 2012, featuring the discovery of the Higgs-Boson and recording-setting quantum teleportation. Keep working on that last one – sometimes it’s too cold to drive anywhere (Wired Science).

3: How bilingualism effects the brains of children, featuring English/Gaelic and Italian/Sardinian speakers. I would like to see something similar done with languages that were less related to each other, but it’s probably hard to find a cohort of Swahili/Thai speaking children…(BBC News)

4: Measuring ice in Barrow, Alaska – the logistical challenges for arctic scientists and what ice can tell us about climate change in progress (Science Friday).

5: Scicurious brings us a Friday Weird Science post on the evolutionary psychology of the romance novel. Steamy and educational (Neurotic Physiology).

Because-I-Feel-Like-It Links

1: This is old but always makes me smile – the entire Doctor Who cast and crew do “500 Miles“, with dancing and the actual Proclaimers. Love, love, love (YouTube).

2: Mormon women around the country dared to wear pants to church last Sunday. Reactions were very mixed. It’s sad that this is even an issue, but I’m glad to see women standing for up themselves in the LDS church. As you might imagine, there has been a lot of chatter about this in SLC (Huffington Post).

3: More depressing news on the Fiscal Cliff negotiations, but at least we get to watch the Republican party destroying itself from the inside. Still, cold comfort to the average citizen facing financial consequences from the bickering (Slate).

4: Tips on how to make resolutions that will stick through the whole this. This is very practical and I’ve found it to be true for myself in the past (The Happiness Project).

5: The Good Men Project may have been attempting to raise awareness of an issue, but what they ended up doing sounds an awful lot like rape apology. You know, because men need to hear more reasons why no doesn’t mean no (Salon).

Things to Do This Weekend – Christmassy Edition

(I realize not everyone celebrates Christmas, but here are a few of the holiday things I plan to do this weekend, which are mainly Christmas themed).

Eat: Home made cinnamon rolls, unapologetically ripped off from Cinnabon. I make these every year around this time, and they will destroy your diet.

Drink: A Christmas cranberry mojito. Looks easy enough to mix up, and very seasonal. Must be a cranberry fan.

Watch: My favorite recent Christmas movie is Arthur Christmas. It looked terrible in previews, but that’s mostly because Hollywood has no idea how to market British movies here. It’s actually adorable and hysterical and not too sappy. If you’re in the mood for something stronger, go for the original Die Hard - it counts as a Christmas movie.

Cook: A Christmas goose! I’ve never done it, but I feel we should definitely bring back the goose as a holiday meal option. We just had turkey at Thanksgiving, let’s try something different! Here are some tips on goose roasting.

Make: Bored of regular paper snowflakes? Geek it up by trying your hand at these Doctor Who and Star Wars snowflakes.

 

Very Chilly Cushions – A Common Plant Adaptation to Life in the Cold

•December 20, 2012 • 5 Comments
Silene acaulis (moss campion), a nearly ubiquitous alpine/arctic cushion plant in the Northern Hemisphere. (Moleda 2012)

Silene acaulis (moss campion), a nearly ubiquitous alpine/arctic cushion plant in the Northern Hemisphere. (Molenda 2012)

I am not sure why, but lately I’ve been thinking a lot about how plants adapt to extremes of cold, both in the arctic and the alpine regions. I’m sure it has nothing to do with the fact that it’s been between 14-17 °F the past few nights, making our uninsulated bedroom a toasty 35 °F.

There are a bunch of interesting and unique adaptations of arctic and alpine plants (which, in fact, are often the same thing), and I plan to provide an overview of those in an upcoming post. Today, however, I just want to cover one adaptation that is extremely common in the tundra, especially in the very harshest parts. Cushion plants.

A cushion plant is not a plant from any particularly family or genus – cushion refers to the growth form the plant takes. And species of plants over a very wide range of groups (at least 30 families) have adapted this growth mode in cold, short seasoned climates, in and around alpine regions worldwide, as well as the arctic and antarctic. If you get high up almost any mountain range, both above and approaching timberline, you will notice that many of the small forbs you begin to see tend to grow very close to each other in clumps. These clumps are usually vaguely circular and ofter appear puffy, like a pillow, though not more than a few inches above the soil. While there are plenty of mat-forming plants in warmer climes, these unique “cushions” are found almost exclusively in alpine/subalpine environments (or arctic/subarctic ones). Cushions typically consist of many smaller plants, which may be vegetative clones of each other or may be genetically distinct, but are often treated as a single organism.

Clearly, the plants derive some serious benefit from this behavior. But what on earth could crowding each other in a resource-limited habitat do to help them? They aren’t like penguins, who generate their own heat and huddle together to share warmth. A cold plant plus another cold plant generally equals two cold plants. (Note: Some plants actually do generate heat, but they are not alpine plants. Rather they tend to be early-spring plants and, oddly, tropical plants). But their genius is in their shape and density.

Azorella compacta (Yareta), a very common cushion plant of the Andean highlands

Azorella compacta (Yareta), a very common cushion plant of the Andean highlands

The dome-like shape which the cushions tend to take (made possible by an adaptation that makes all the plants in the clump grow upward at the same rate, so no one plant is high above all the others), and the closeness with which those plants grow, makes these clumps perfect heat traps. The temperature on or inside a cushion can be up to 15 °C more than the air temperature above it. The cushions are able to retain heat radiating up from the soil, as well as absorbing heat from the sun (a very dense, large, clump of green can get surprisingly warm on a sunny day at high altitude). Add to that the fact that the wind speed in and around a cushion can be cut by up to 98% from open areas, you have a perfect recipe to prevent heat loss. Many alpine cushion plants also have very hairy leaves, which trap even more heat within. This allows the plants to maintain a relatively stable, warmer than average microclimate that is resistant to sudden changes in weather and temperature outside (such as freezing temperatures at night or sudden storms). Interestingly enough, this stabilizing effect can also be a benefit when it gets too hot out, maintaining lower temperatures against baking sunshine.

The benefits of a cushion-like growth form at high altitudes go beyond just heat retention and wind protection – they also extend to increasing soil moisture and nutrition in the area beneath the cushion. Cushion plants, like most alpine plants, have a large, deep taproot. Because alpine soils often drain quickly and are poor in nutrients, a long root system is important for the plant to be able to reach enough water and nutrition. Most alpine plants are perennial and die back to their roots in fall, having to exist on stored resources throughout the 10 month dormant season, and a thick taproot can help with that. In addition, in a place with high winds, snow, and not a lot of other plants around, a good anchor is vital. Cushion plants have the advantage of having a root system that is not just deep, but also extensive, consisting of one or more taproots and a network of entangled smaller roots closer to the surface. These help trap water and nutrients where the plant can get at them, and the dense cover provided by the cushion drastically cuts evaporation. This is not an insignificant effect; some research has shown that soil moisture in cushion sites can be increased up to 70% above non-cushion sites, and available nitrogen up to 90%.

 The mean community composition estimates for plants and arthropods associated with cushion plants and open non-cushion vegetated microsites. Note how the cushion positively effects all measurement except, in this case, diversity of plants. (Molenda 2012)

The mean community composition estimates for plants and arthropods associated with cushion plants (Silene acaulis) and open non-cushion vegetated microsites. Note how the cushion positively effects all measurements except, in this case, diversity of plants. (Molenda 2012)

Cushion plants often start out by colonizing completely bare soil, in the harshest of climates. As you can imagine, the process of getting started without any existing buffering cushion is a little bit problematic, so new cushion establishment is actually rather rare. That’s okay though, because depending on the species a single cushion can reach up 350 years old (and some Andean species are claimed to have reached 3,000). The cushion grows very slowly, much more so than lower-elevation plants, but can eventually reach up 3 m in diameter. Cushion species also tend to have very large showy flowers, often strongly smelling, for their small size, which may bloom all at once, attracting a greater number of pollinators than if they had smaller flowers or grew more sparsely.

As you can imagine, all these factors contribute to making these cushions ideal microclimates in a very inhospitable habitat. What’s really interesting is that although cushions of the same plant may reach from the subalpine or even montane habitat to well past timberline and onto nearly bare, windswept ridges, the general conditions inside the cushion remain fairly constant. So at a lower altitude the relative difference in conditions from open ground may not be very large, but as the environment becomes higher and colder and windier, conditions in the cushion will be vastly different, while still resembling conditions inside the lower-altitude cushion of the same species.

The desirable microclimate created by the cushion is not just desirable for the plant itself – in fact these plants have been shown to provide habitat for other plants, which shelter under the canopy of the cushion, as well as a variety of microorganisms and arthropods. Studies on various species of cushion plant around the world have shown that, depending on the type of plant and the location, cushion plants may improve species diversity, richness, or evenness (often all three!) when compared to a similar site with no cushion. This has led to cushion plants being variously known as “nurse plants“, “ecosystem engineers“, and “foundation species“. All these terms have different exact meanings, but in general refer to a species that alters its environment in such a way that is beneficial or even vital for a number of other species or individuals in that ecosystem.  In fact, the higher up slope you go and the more relative difference between conditions in and outside of the cushion, the more important to other species cushion plants seem to be.

Works Consulted:

Badano, E. and Cavieres, L. (2006). Impacts of ecosystem engineers on community attributes: effects of cushion plants at different elevations of the Chilean Andes. Diversity and Distributions, 12(4): 388–396.

Cavieres, L., Arroyo, M. T.K., Peñaloza, A., Molina-Montenegro, M. and Torres, C. (2002), Nurse effect of Bolax gummifera cushion plants in the alpine vegetation of the Chilean Patagonian Andes. Journal of Vegetation Science, 13: 547–554.

Cavieres, L., Badano, E., Sierra-Almieda, A., and Molina-Montenegro, M. (2007). Microclimatic Modifications of Cushion Plants and Their Consequences for Seedling Survival of Native and Non-native Herbaceous Species in the High Andes of Central Chile. Arctic, Antarctic, and Alpine Research, 39(2): 229-236

Molenda O, Reid A, Lortie CJ (2012) The Alpine Cushion Plant Silene acaulis as Foundation Species: A Bug’s-Eye View to Facilitation and Microclimate. PLoS ONE 7(5): e37223

Morris, W. and Doak, D. (1998). Life history of the long-lived gynodioecious cushion plant Silene acaulis (Caryophyllaceae), inferred from size-based population projection matrices. American Journal of Botany, 85 (6): 784-793

Old Bones, New Conservation Tool

•December 19, 2012 • 1 Comment

Let me start out by saying I love Yellowstone National Park. It is easily my favorite place I’ve ever been to. So I’m always excited when new research comes out of Yellowstone, particular when it’s research that could mean a lot for conservation in the park and elsewhere.

A recent paper in Ecology by Josh Miller outlines a new method of using bone assemblages of elk in Yellowstone as a means of discovering things about the population both in time (how the population changes over decades) and space (how the animals use the resources available to them). While the Yellowstone ecosystem has been very heavily studied, especially for the last 20-30 years, there are still plenty of gaps in the data, particular in terms of historical records about any given species. It’s important to understand as long a span of history about a population as is possible, so that you can tell if short term changes in a population’s structure, abundance, or movements are just a natural fluctuation or indicative of a trend or permanent shift. The better the historical data, the better conservationists can accurately determine how to manage a population (and know whether it’s in trouble).

The problem is the kind of decades-long, multi-generational studies required to gather this kind of data are hard to get funded and difficult to maintain over the careers of perhaps several researchers. And even if a very long term study starts now, that doesn’t help provide historical data from a hundred years ago or more. So conservation ecologists try to find other methods to learn about the habits of previous generations of populations, such as looking at soil cores, but it can be hard to find a method that is reliable across the board, particularly for different species. In addition, large, migratory mammals present a special challenge, because scientists need to know their seasonal movements as well as the population structure.

When reading the paper, I was surprised at how seemingly simple the concept behind it was, and that it hadn’t been thought of until recently. Scientists have used bone assemblages previously to determine things about the structure and abundance of a population, but using them to learn about populations over a long period or their seasonal movements is a pretty new idea, and one that had never been tested on a large North American mammal before.

Miller didn’t originally set out to study modern ecosystems or develop a new tool for conservation. He’s a paleontologist by training and was originally looking for a reliable way to estimate population size of certain dinosaurs, based on the fossil record. To do this, he needed to compare a live population of large animals to the bones they left behind and come up with some kind of ratio that could be applied to extinct animals. But once he started studying ungulates, he realized that there was much more data in the bones that was not being put to use. Part of the reason for this is that bones have generally been considered only to persist a short time in nature, but in fact they can hang around on the surface for decades to more than a century. In addition, it’s fairly easy to tell approximately how old a bone is by its rate of weathering.

Antler and neonatal bone concentrations within the study area (Miller 2012)

Antler and neonatal bone concentrations within the study area (Miller 2012)

In this study, 1 km square plots were established in 4 different habitats (grassland, lake margin, conifer forest, and river margin) across the study area, without regard for any current data on elk migration or use of certain areas. Researchers walked a set transect (line) though the study plots, recording every bone of every kind they could see. The main area of interest to this particular study were the antlers shed by male elk during the winter and the bones of recently born baby elk. The reasons for this is that there is an abundance of both (all males shed their antlers and the infant mortality rate for elk can be upwards of 80%), and that both of these say something specific about the elk’s seasonal habits. Antlers are a clue to the elk’s annual wintering grounds, and an abundance of calf bones points to the seasonal calving areas, both major yearly events that dictate the animals’ migratory patterns.

Surveys were conducted three years running, and then the data on antlers and neonatal bones were compared with aerial surveys of live elk over a decade. It was found that the bone assemblages can accurately delineate elk wintering and calving grounds, by using the bone concentration to estimate the expected number of live elk found there. In fact, for bull elk wintering grounds, the method was found to be even more consistently accurate than live aerial surveys.

Comparison of survey methods for bull elk wintering grounds (Miller 2012)

Comparison of survey methods for bull elk wintering grounds (Miller 2012)

The reason this is so exciting is that not only is there now a useful method for prediction a modern population’s use of the land through bone assemblages, but it allows scientists to study how the land use has changed over time. Bone assemblages from the past where no or few live elk or recent remains are found means that the animals’ habits have changed. Live surveys provide a snap shot of what is happening in a particular season, and when combined over several years or decades provide a short term view of populations changes. Bone assemblages are averaged over a long period time and provide excellent data on the population for up to a century past.

In addition, bone surveys like this can take place in the summer and still provide data on winter usage, and are in general less expensive to perform than aerial surveys. They can be superior in certain habitats, such as densely forested areas where it is difficult to see the animals from above. Bone surveys are also less invasive than most live surveys for the animals, thus less likely to change their behavior due to observation, and safer for researchers.

This study also opens the door for exciting new possibilities, such as maybe using approximate ages of bones to gain data on changes in use and abundance of populate by decade, instead of only a time-averaged view. I really look forward to seeing where this research leads, both in Yellowstone elk and when applied to other species. It seems like this technique is really starting to catch on for many different kinds of animals in various habitats and I think it will prove to be a very important conservation tool in the future.

(Note: I have only outlined the central conclusion of this research, there are many other interesting facets to it. I would encourage everyone to read the paper, as well as Miller’s previous one, to understand the full scope of the study and methods/calculations used)

Works Consulted:

Farke, A. (8 April 2011). Life After Death At Yellowstone: An Interview with Josh Miller (The Open Source Paleontologist blog). Retrieved 12/19/12.

Lester, Liza. (10 December 2012). Elk bones tell stories of life, death, and habitat use at Yellowstone National Park (ESA Ecotone blog). Retrieved 12/19/12.

Book Review: American Bison

•December 12, 2012 • Leave a Comment

american-bisonWhat? Two blog posts in two days? What kind of insane world is this?

I wasn’t sure what to expect when I picked up American Bison: A Natural History by Dale E. Lott, other than a lot of information about bison, obviously. I kind of thought it would be a dry, technical volume, which I wouldn’t have minded too much, but I was pleasantly surprised to find a broad, accessible summary of bison ecology and behavior.

The author not only has done a large amount of research on bison behavior, but he grew up in and around the National Bison Range in Montana, with a father and grandfather who worked managing the herds. He provides a knowledgeable, enthusiastic, and even loving voice for his topic, without seeming overly sentimental or dogmatic about any of his subjects.

The book is organized into several sections, including ones on behavior, biology, history, conservation, and other organisms’ interactions and influence on the bison. In each section he gave some basic, general information about the topic he was pursuing and then went into detail on just a few specific areas in that larger subject. I appreciated this approach, because he provided the the reader a basic foundation to work on as well as really getting into the science and providing information that even people familiar with bison might not know, without overwhelming the reader with more facts than they could remember or too much jargon for the layperson.

The strength of this book was really in its accessibility to the topic (without dumbing down too much) and in its breadth. It lives up to its subtitle “A Natural History” in that it really attempts, and mostly succeeds, in providing a relatively complete picture of the species, past, present, and potential future. I would recommend this book for the casual bison lover looking to learn more, and to anyone interested in wildlife ecology in general, but who maybe doesn’t know much about the basics. It provides a good introduction to larger ecological and conservation concepts as part of the case study of bison, but in a way that is broadly applicable the field as a whole.

One last thing I particularly noticed and appreciated was that while the author did talk about his own research a lot, he included research from other sources and was careful to talk about ways in which the research differed. This was most notable in the section on behavior, where bison behavior varies greatly between several populations that were studied (this seems to be due to resource availability). I think it’s important to show that a species is not always homogenous across its range, and that different studies may show different results, for a variety of reasons.

“American Bison” is not a perfect book, but it is well-written, informative, and a fairly quick read for a popular science book. I wouldn’t recommend it for someone already moderately well versed about bison ecology, as it is unlikely they would find any new information in it, or for someone looking for a lot of detail about any one aspect of bison natural history (such as the history of bison hunting or their digestive biology). But it’s great for the beginner enthusiast and even for more serious students of ecology who have general knowledge but not much specific knowledge about this American icon.

Pikas Pick Phenol-Heavy Plants to Preserve

•December 11, 2012 • 2 Comments

A blog? What do you mean I have a blog? Oh…this blog. Right. Sorry folks (and by “folks”, I mean the five people a week my traffic counter says still visit this dry and forsaken land), apparently consistency is not my strong point! But since I’m currently unemployed I really have no excuses to not get back in the swing of science blogging. So to celebrate my return to the internets, I’m going to start with a little post on one of my favorite local mammals: the pika!

734px-Ochotona_princeps_rockiesMost of you probably know this, but despite how adorably mousy our fluffy pika friends look, they are actually not rodents. They are lagomorphs (bunny relatives), and they live in alpine habitats – mainly over about 8,200 feet in our area. There are 30 known species of pika, but only two in North America, and the American Pika (Ochotona princeps) is the one most people are familiar with (Ochotona collaris lives in Alaska and Canada), so that’s the one I’ll be talking about.

Pikas are really quite amazing because they live in extremely inhospitable areas – cold climate, high elevations, and steep, rocky talus slopes. In many parts of their range the growing season is only about two months long, and as herbivores who rely mainly on grasses and forbs (herbaceous broad-leaved plants) they pretty much have to gather and store ten months worth of food in those two months, as well as continuing to feed themselves and put on weight for the winter at the same time. The activity of gathering food to store for later is called “haying” (insert image of pika in overalls and holding a pitchfork here).

If you see a pika on a hike, chances are it has a mouthful of grasses or leaves that it’s taking to cache in various locations beneath the rocks. One study found that pikas make around 14,000 trips to gather food over an 8-10 week season! Storing food for the long cold season is vital for them because, unlike so many other small mammals that live in similar conditions, pikas don’t hibernate. They are active all year long, even if most of that time is spent being active under the snow, in their talus slope burrows. While they do manage to collect some food during that time, in the form of lichen and evergreen plants, the main source of sustenance comes from their food caches.

But, as you might imagine, storing food for 10 months or more can be a problem, particularly when what you’re storing is leafy plant material. Plants decompose, they get moldy and develop bacteria, they lose nutritive value. How can a pika possibly ensure it has food stored that will keep all year?

Well, the genius of the pika is that it turns the plants’ own defenses against them. Plants don’t like having their leafy parts eaten, because it reduces their ability to photosynthesize, so they have evolved countless ways of discouraging predation by herbivores, and the herbivores have co-evolved countless ways overcoming those defenses. One of the main ways plants make themselves undesirable or inedible is to produce toxic compounds, the most common of which are tannins and other phenols, which make them unpleasant to eat and difficult or impossible to digest. Some animals have evolved a resistance to these compounds, such as enzymes or gut bacteria that help break them down, but the pika does something else entirely.

In the summer months, the pika will gorge itself on plants that are low in phenolic compounds, as they are readily digestible. But it will select a range of plants to store for later that are higher in phenols. The pika won’t eat these plants immediately, it caches them for the winter. The reason for this is that phenolic compounds don’t just discourage predation, they also act as a preservative. Plants higher in phenols don’t decompose as quickly as the more immediately-desirable kinds. What’s more, as they age, the toxins break down as well, rendering them edible and what’s more, more nutritious than plants stored for the same time that were low in phenols to begin with.

Turns out pikas can tell the difference between plants with high and low phenol levels; even when they are presented with a choice of plants which are the same species but individually have differing phenol levels, pikas selected the lower level plants for immediate consumption. This is a fantastic strategy for a creature like the pika. They eat the most nutritious and digestible food first, then move on to the other plants as they become more consumable over time, while at the same time ensuring they have supply of food throughout the whole winter and that it will remain nutritious and safe to eat (due to anti-bacterial and anti-fungal action of the phenols). The pika has completely co-opted the plant strategy for it’s own benefit.

Sadly, these little guys may be among the species most effected by climate change, as warming temperatures reduce their habitat and force them to move to higher elevations to combat the heat. However, in the past year there has been new evidence of pikas living at lower elevations than it was previously thought that they could tolerate, so perhaps the pika is even more adaptable than we think. Given their clever food storage habits, it wouldn’t surprise me.

Dearing, D. M. 1997. The Manipulation of Plant Toxins by a Food-Hoarding Herbivore, Ochotona Princeps. Ecology. Vol. 78, No. 3, pp. 774-781
Smith, M. T. and M. L. Weston. 1990. Ochotona Princeps. Mammalian Species. No. 352, pp. 1-8
 
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