SPECIES BIOLOGY of SAGEBRUSH STEPPE:
Species Biology can be described by a Species’ life strategies. Life strategies are how an organism allocates energy and materials to be able to compete in an environment, to survive and reproduce. Evolving through natural selection, developing tradeoffs of growth/survival/reproduction; life strategies are a sum of a species’ morphology, physiology, environmental responses, resource requirements, energy acquisition, storage and allocation, reproduction strategy, and life cycle. The main life strategies of Sagebrush Steppe Species evolved to be adaptations to heat and aridity (drought).
Plants
Photosynthesis is the foundation of the food-chain, providing energy for all trophic levels. Solar radiation is used to convert H20 and C20 into carbohydrates that produce energy for plants and animals. There are three photosynthetic pathways that evolved/adapted and thrive in different environments: C3, C4, and CAM. Plants are Primary producers, in that they produce energy by using sunlight to synthesize water and carbon dioxide into carbohydrate, for all upper trophic levels of the food chain.
C3 pathway produces 3-Carbonic acid. There is a one step carbon fixation process in which CO2 is fixed by Rubisco directly in the chloroplasts of a plant. C3 plants have the most ancient pathway because they evolved first, during a time period of high CO2 concentration and low O2. Therefore C3 plants can be inhibited by high levels of O2, an issue called photorespiration: where O2 binds to Rubisco instead of CO2. They are cool season plants, sensitive to warm and dry climates (thriving in temperatures 65-75 degrees F).
C4 pathway produces 4-carbonic acid. It can perform the one step function of the C3 pathway; or it can use ATP as energy for a two step process that reduces photorespiration. This two step process involves PEPcase acting as the initial receptor of CO2, not Rubisco. PEPcase has high affinity for CO2 and none for oxygen. Temperature ranges from 90-95 degrees F, so they are warm season plants. C4 plants evolved after C3, during a period with high O2 concentration.
CAM plants have evolved adaptations that conserve water in hot and arid environments, with high evapotranspiration. Stomata open in the nighttime (dark) instead of daytime (light), when CO2 enters the plant. CAM plants start photorespiration with PEPcase without solar radiation, and continue in the daytime when light is available. CAM plants are most closely related to C4 pathway, the most recently evolved pathway.
The dominant types of plants in a Sagebrush Steppe ecosystem are shrubs and grasses including Basin Big Sagebrush, Antelope Bitterbrush, Idaho Fescue, Bluebunch Wheatgrass, Rubber Rabbitbrush, Green Rabbitbrush, Cheatgrass, Ventenata, Sandberg Bluegrass, and Basin Wildrye. The general adaptations are to drought (aridity) and heat, with abundant vegetation in areas with enough precipitation to support shrubs and grasses, but not trees. They survive in the system by lasting through snowy winters and hot, dry summers. The dominant vegetation is plants that can survive in a semi-arid environment. The adaptations to heat and drought include mechanisms to survive the low precipitation, low temperature, heavy winds, and high salinity of semi-arid environments. Sagebrush Steppe ecosystem include plant species adapted for wind-dispersed seed pollination. Soil quality involves clusters of bacteria, algae, moss, and lichen growth. These soil features are heat and arid resistant, as well as fix their own nitrogen. This influences soil stability and erosion control, water infiltration, nitrogen fixation, facilitate seed germination, and nutrient cycling. Whether adaptations of Avoidance (dependent on precipitation) or Tolerance (leaf polymorphism, stem photosynthesis, and phreatophytes to reduce transpiration/photosynthesis) or Resistance (many CAM plants resistant to heat and aridity), plants have evolved to survive in a variety of different environments of heat and drought.
Animals
The Species Biology of Animals in Sagebrush Steppe Ecosystems involves behavioral adaptations to heat and drought. The main habit of animals as an adaptation to heat and aridity is Avoidance. Animals can be: nocturnal, where they are active at night (e.g. javelina); crepuscular, where they are active at dawn and dusk (e.g. coyote). To avoid heat; animals may burrow, seek shade of plants, or hide between rocks. Behavioral adaptations have evolved to seek cool micro-climates. Thermal Inertia is an advantage of larger mammals, whose bodies take longer to heat up. The dominant types of animals in Sagebrush Steppe ecosystems include Pygmy Rabbits, Coyotes, Sagebrush voles, Sagebrush lizard, golden eagles, Pronghorn, mule deer, elk, Kangaroo Rat, owls, livestock (cattle and sheep), wild horses, jackrabbits, and Sage Grouse (2). General adaptations include heat and aridity. These animals also depend on Sagebrush ecosystems for energy and nutrition. For example, the Pygmy rabbit is 99% dependent on a diet of Sagebrush in the winter to survive.
Other adaptations to heat and drought include morphological and physiological characteristics. The three categories include heat dissipation, evaporative cooling, and alternate water acquisition. Heat dissipation can involve shedding or in cases like the Jackrabbit, long/tall ears have dilating blood vessels that dissipate body heat to air. Evaporative cooling is when an animal cools itself through evaporating water from it’s surface; such as when an animal pants, or through it’s nasal passages. Alternate water acquisition involves a physiological process that regulates and balances internal water availability of an organism in the face of heat and drought. For example; the Pronghorn eats cholla fruit to obtain water and nutrients when there is limited water. A Kangaroo rat may utilize oxidized water from seeds, or retain water by use of concentrated urea and dry feces.
Citations
Gibson, Yvette. “Chapter 2: Species Biology”. Oregon State University. 2018.
U.S. Fish and Wildlife Service. “Why care about America’s Sagebrush”. USFWS. 2014. https://www.fws.gov/mountain-prairie/factsheets/Sage-steppe_022814.pdf
