Population Ecology of Sagebrush Steppe

Population Ecology provides information on populations of species, indicating the long term sustainability of that population and the degree to which a species utilizes it’s available habitat. Population can be defined as the individuals of a particular species that occupy a certain area.

Demography is the study of how a population of a species changes over time; including population size and density, distribution, and survivorship type. The dominant vegetation species of Sagebrush Steppe is Big Basin Sagebrush, while examples of some of the dominant Wildlife Species is mule deer (1) and Burrowing Owls (7).
Population Growth and Control describes that there a variety of factors that influence changes in population size and density; density independent factors and density dependent factors. Density dependent factors can be geometric (e.g. periodic reproduction such as when deer reproduce annually), or exponential (e.g. continuous reproduction such as when rabbits reproduce at any time); if resources are unlimited. Since resources are not unlimited, a system will only support a maximum number of individuals, and a population will reach Carrying Capacity and slow or decline. Birth and death rates must be balanced to avoid growth, until migration or habitat area expands producing more resources. Therefore, Density Dependent can be defined as the regulation of population size based on its relation to carrying capacity. Density independent factors are regulated by environmental factors such as drought/wildfire or community dynamics such as predation/allelopathy.

Population distribution and dynamics are influenced by both abiotic and biotic factors. The two main abiotic factors are physical geography and climate, while the biotic factors include species interactions: allelopathy, predation, competition, mutualism, etc.

Disturbance and Climate Change involve a variety of different factors. Disturbance may be related to invasive plants, fire, drought, grazing, agriculture, urbanization, recreation. Climate Change involves shifting of climatic factors such as precipitation, temperature, wind, and pressure fronts in its variation, intensity, or global distribution. Shifts in climatic factors can influence change in species population dynamics and distribution. Since Biogeography is dependent on climate and geology, shifts in climate will produce biogeographic shifts for a species range.
The following examples of demography, population growth and control, and disturbance and climate change in Sagebrush Steppe ecosystems focus on one dominant vegetation species, and one dominant animal species.


The dominant vegetation of Sagebrush Steppe is Big Basin Sagebrush (Artemisia tridentata var. (ssp. tridentata)):

Demography- Native to the Intermountain Western United States, Great Basin, the lifeform of this vegetation is shrub and it is resistant/tolerant to drought. It has a perennial life cycle, a fast growth rate, and fast regrowth rate. Capable of allelopathy, can grow 2-15 feet depending on environment. Adaptable to sand, loam, or clay soil with fine, medium, or coarse texture. Big Basin Sagebrush has a high tolerance for CaCO3 and grows in deep, seasonally dry, well drained soil with a minimum depth of 3 ft. It requires a minimum of 110 frost free days, and moderate moisture use. Grows in Soil pH 6.5 to 8.5, slightly acidic to slightly basic soil. Receives low precipitation, 10-19 inches annually. Flowers August to October and reproduces by seed in Fall and Winter. Seedling Vigor is Moderate and depends on precipitation, seeds sheltered by mature sagebrush are more likely to survive. This means that Big Basin Sagebrush populations survive in semi-arid environments with deep rooted soil.

Population Growth and Control- The abiotic factors that influence population dynamics include the geographical and climatic characteristics previously discussed in the Demography section of Big Basin Sagebrush. So this species may increase in population size/density where these environmental factors apply, and will be less abundant where they do not. One major biotic factor that influences population dynamics is allelopathy, a species interaction that helps Big Basin Sagebrush compete with other vegetation through inhibiting the other plant.

Disturbance and Climate Change- Big Basin Sagebrush has a long life span of 40-50 years but does not resprout after disturbance, such as fire (8). It is important to consider fire in land management of this species, because this disturbance will wipe a population from a community. Climate change results in higher temperatures and lower precipitation, influencing an increase in fire frequency and intensity; and possible reduction of Big Basin Sagebrush.


One dominant animal species of Sagebrush Steppe is Mule Deer (Odocoileus hemionus):

Demography- The rate of movement shows that mule deer have crepuscular activity patterns (3). Deer densities are high along the Columbia River, and where trees may serve as a food source, visual and thermal cover for protection (3). Natural factors that affect homerange include topography, season, food availability, mating activity, population density, and cover density (3). This species has lower and more variable fawn survival, but is compensated by high fecundity rates (4). They will move to higher elevation during hot periods, and lower elevation during colder periods (1)

Population Growth and Control- Mule deer are affected by both Density Dependent and Density Independent factors. Predation (density independent) is the highest cause of mortality, but balances out the high deer densities (4). Mule deer are limited by forage availability (density dependent) and climate (density independent). They also reproduce annually (density dependent). Population Dynamics of mule deer include populations are limited by both forage availability and climate, adult females are limited by forage availability, while fawns are limited by both forage availability and predation, and population growth is constrained by fecundity and fawn predation; and overall can be destabilized if large changes in the abundance of predators or alternative prey change predation risk (4).

Disturbance and Climate Change- In response to human disturbance mule deer will exhibit behavior to avoid risk, resulting in less food availability near anthropological activity; and indirect habitat loss 4.6 times greater than direct habitat loss (2) This is important for management in energy development, as indirect habitat loss due to human avoidance reduces mule deer populations, as mule deer carrying capacity is limited by forage availability (2). Whether directly or indirectly; mule deer populations will decline or slow in response to urbanization and human activity. Immediate response to the disturbance of fire is to flee, but this species may seek out recently burned sites that have more fertile and productive shrubland vegetation. In response to climate, mule deer will migrate due to deep snow and cold temperatures (6). Climate change results in changes in biogeography and vegetation dynamics, resulting in a changing environment and range for the mule deer. Less forage will result in reduced habitat.


Arizona-Sonora Desert Museum. “Animal Fact Sheet- Mule Deer”. Arizona-Sonora Desert Museum. 2008. https://www.desertmuseum.org/kids/oz/long-fact-sheets/Mule%20Deer.php
Dwinell, Samantha, Kevin Monteith, Hall Sawyer, Gary Fralick. “Effects of human disturbance on the Nutrition ecology of mule deer”. Wyoming Game and Fish Department. 2017. https://wyocoopunit.org/projects/effects-of-human-disturbance-on-the-nutritional-ecology-of-mule-deer
Eberhardt, Lester E., Eric E. Hanson, Larry L. Cadwell. “Movement and Activity Patterns of Mule Deer in the Sagebrush-Steppe Region”. The American Society of Mammalogists. Journal of Mammalogy. 1984. https://academic.oup.com/jmammal/article-abstract/65/3/404/850660
Forrester, Tavis and Wittmer, Heiko. “A review of the population dynamics of mule deer and black‐tailed deer Odocoileus hemionus in North America”. Wiley Online Library. 2013. https://onlinelibrary.wiley.com/doi/abs/10.1111/mam.12002
Gibson, Yvette. “Ch 3: Population Ecology”. Oregon State University. 2018.
Monteith, Kevin L, Vernon C. Bleich, Thomas R. Stephenson, Becky M. Pierce, Mary M. Conner. “Timing of seasonal migration in mule deer: effects of climate, plant phenology, and life‐history characteristics”. Ecosphere. Ecological Society of America. 2011. https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/ES10-00096.1
Rich, Terrell. “Habitat and Nest-Site Selection by Burrowing Owls in the Sagebrush Steppe of Idaho”. U.S. Bureau of Land Management. The Journal of Wildlife Management. Vol. 50, pp. 548-555. Oct., 1986. http://www.jstor.org/stable/3800962?seq=1#page_scan_tab_contents
Young, James and Evans, Raymond. “Population dynamics after Wildfire in Sagebrush grasslands”. Journal of Range Management. Vol. 31, No. 4 pp. 283-289. 1978. http://www.jstor.org/stable/3897603?seq=1#page_scan_tab_contents

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).

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.

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.


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

Biogeography of Sagebrush Steppe

Solar Radiation And Geographic Location

Sagebrush Steppe Ecosystems are geographically located in the Northern Mid-Latitude(30 to 45 degrees North) region of approximately 40 million hectare of the Western UnitedStates (3) (Oregon, California, Idaho, Wyoming, Utah, Nevada), providing habitat for 350 vertebrae species (1). Solar radiation reaches Earth as insolation, and due to distance and angle of Earth from the Sun, insolation intensity decreases as you move farther from the equator.Declination is the point where insolation is at a maximum, and moves from 23.45 degrees North to 23.45 degrees South, which results in seasonal change (1). This also results in more variation between day/night length and maximum/minimum daily temperatures as you move away from the Equator, due to Earth’s rotation around the sun and declination (position of sun with respect to the equator). Northern Mid-Latitude regions have the warmest temperatures from June-August and the coldest temperatures from December to February, with a variation below 0 degreesCelsius to above 30 degrees celsius. Sagebrush Steppe ecosystems occur at elevations from 150to 2000 meters (500-6550 ft), with an average elevation of 1235 meters (4052 ft) (1). Vegetation is abundant Sagebrush with other shrubs, grasses, and flowering plants. Terrain is typically flat valleys and plains or gently rolling hills located in the Sierra-Nevada Mountains, CascadeMountains, and Rocky Mountains. There are 3 physiographic regions in the Intermountain West(2) including the Colorado Plateau, Great Basin, and Columbia-Snake River Plateau. Sagebrush steppe does not make up the Colorado Plateau (1).

Weather can be defined as the day to day state of the atmosphere (1). Climate can be defined as the patterns of precipitation, temperature, humidity, barometric pressure and wind over time (1). The main inputs influencing climate are solar radiation, Earth’s atmosphere, andTopography. Solar radiation heats the Earth’s surface producing wind patterns and the water cycle, influencing the distribution of weather patterns. Precipitation is the main determinant of vegetation production (1). In Sagebrush Steppe Ecosystems, precipitation falls in low amounts at9.84 inches or 200-500 mm per year, with an average of 250 mm per year (1). Due to the northern latitude location, elevation, and topography; precipitation falls mainly in the form of snow. A Mid-latitude location results in uneven distribution of solar radiation; influencing variation in photoperiod, which effects growing season of plants, daily duration of
photosynthesis, produces semi-arid plant communities, and an Orographic effect due to theCascades and Sierra-Nevada Mountains to the West and Rockys to the East. Due to the*Orographic effect, Precipitation is driven by global wind patterns and warm air flows inland off of the Ocean and crashes into a mountain. The warm air rises, cools, and the moisture condenses to fall as rain. As the air mass moves over the mountain and loses moisture as rain, the air becomes dry on the other side. Therefore, as warm air moves inland off of the Pacific Ocean, it hits the westward side of the Cascades and Sierra Nevada Mountains, rises and cools and falls as rain on the Westward side of the Mountains, then becomes dry as it rests on the Eastward side of the Mountains. Therefore, the dry air produced by the Mountains settles and produces a semi-arid environment that supports a Sagebrush Steppe Ecosystem.The Sagebrush Steppe Ecosystem land uses include forage for livestock, habitat for wildlife, aesthetic value of open space, cultural heritage of the West, energy development like wind and solar energy, and a high quality water source (4). Landscape considerations include habitat degradation such as fragmentation, erosion, decreased water quality, reduced forage and habitat, fire (suppression), converting land to agriculture, and drought (3).


Climate influences vegetation communities, water cycling, and Sagebrush Steppe ecosystem function because of temperature and the amount of precipitation. Temperature affects the rate of evaporation, degree growing days, and frost period; influencing the type, species, and abundance of a plant community. Sagebrush Steppe Ecosystems have temperatures from 34.6 to100.4 degrees F (1), and are therefore warm and dry in the summer, and colder with frost in the winter. Since precipitation is the driving factor of vegetation production (5); the low amount of precipitation in Sagebrush Steppe Ecosystems results in enough water to support grasses and shrubs, but not enough to support large amounts of trees. In Sagebrush Steppe Ecosystems; water flows through shallow creeks and contributes to the water cycle through evaporation, and is absorbed by plants and contributes to the water cycle through transpiration. A warming climate means more evaporation and less precipitation; which results in less vegetation, increased runoff,and erosion.


Topography influences vegetation communities, water cycling, and Sagebrush Steppe ecosystem function because it influences climate and geology. For example, temperature decreases as elevation increases, precipitation falls as snow (1). The main topography of Sagebrush Steppe is the formation of basins (valleys) and range (Mountains) (1). SagebrushSteppe topography includes flat valley, rolling hills, or foothills. The Orographic Effect (*refer toSolar Radiation and Geographic location) is the main reason that the Topography (Mountains
and Valleys) of the region influences the semi-arid environment of the Sagebrush SteppeEcosystem.


Soil is the primary determinant of the type of plant species in any given area. It’s influence is determined by parent material, soil organic matter, texture and structure, pH and salinity, and physical/biological crusts. Sagebrush Steppe Ecosystems have parent material that is volcanically derived with sand and clay particles. The Soil Orders and Suborders in this ecosystem include Aridisols ((Arigids and Cambids)) but also Mollisol (Ustolls and Xerolls) and Andisol (Xerands) (1). Aridisols occur in arid regions, Mollisols are dark in color because ofOrganic matter and rich in nutrients, and Andisols are derived from volcanic ash. The ColumbiaRiver region contains Loess Soils, while the Great Basin has deep alluvial soil (1). Soil is formed through primary succession of parent material such as Sedimentary, Igneous, and MetamorphicRock. Soil horizons build up as parent material mixes with Organic matter. Soil Organic Matter(SOM) reflects the fertility of a system and influences nutrient cycling, carbon sequestration, soil structure, plant rooting, water infiltration, water holding capacity, and microbe habitat. SOM amount and rate is affected by precipitation and temperature. Sagebrush Steppe has moderate levels of SOM. Soil texture and structure of a Sagebrush Steppe ecosystem is greatly affected by degradation. For example, human activities, wind, and water can put pressure on soil aggregate sand contribute to degradation. However, aggregate stability is important for erosion control,water infiltration, nutrient availability, and facilitating root growth.

(1)Stewart, Kandy. “Sagebrush Steppe Module”. Oregon State University. 2017.
(2)National Park Service. “Sagebrush Steppe”. NPS.gov. 2017.https://www.nps.gov/crmo/learn/nature/sagebrush-steppe.htm
(3)McIver, J.D.; Brunson, M.; Bunting, S.C., and others. 2010. “The Sagebrush SteppeTreatment Evaluation Project (SageSTEP): a test of state-and transition theory.” Gen.Tech. Rep. RMRS-GTR-237. Fort Collins, CO: U.S. Department of Agriculture, ForestService, Rocky Mountain Research Station.https://www.fs.fed.us/rm/pubs/rmrs_gtr237.pdf
(4)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
(5)J.D. Bates, T. Svejcar, R.F. Miller, R.A. Angell. “The effects of precipitation timing on sagebrush steppe vegetation”. Journal of Arid Environments. 2005.

The Great Plains

Main characteristics of grassland areas:

Tallgrass Prairie

The most mesic of all central plains grassland types: receives the most rainfall, greatest longitudinal diversity, and greatest abundance of dominant species (Sims 271). From Tallgrass lecture, 500-1000 mm precipitation annually, mostly in Spring and Summer.
Large ecological amplitudes and geographical range (271)
Vegetation is long-lived perennials, and varies with climate and soils; primarily bunchgrasses and sod-forming grasses (271).
Three grassland Associations: Bluestem/True Prairie, Nebraska Sandhills, and land from Canada to Kansas/Nebraska/The Dakotas (271).
Most now in cultivation- used for livestock grazing (272)
Fire suppression has led to an increase in woody vegetation (273)

Mixed-grass Prairie:

Serves as an ecotone – Blend of Tallgrass and Shortgrass Prairies (274)
Lies west of the Tallgrass Prairie (274)
Richest floristic complexity of the grasslands; vegetation includes intermediate/short stature grasses, tall grass, forbs, suffrutescens, and low growing shrubs (274).
Vegetation fluctuates due to climate (Shortgrass will occur in more arid environments and is more drought tolerant), fire suppression, and livestock/wildlife grazing (275).
Associated with rolling topography (275).

Shortgrass Prairie:

Large expanse of vegetation east of the Rocky Mountains (278)
Cool season grasses in the north, shortgrasses dominate the west, while tall grass and mixed grass is more prominent in the East (278)
Evolved to adapt to grazing- first buffalo and then domestic livestock
Location of the 1930s Dust Bowl in which the shortgrass prairie was plowed for farming (278)
Fire is detrimental to most vegetation (279)

California Grasslands:

Known as the Pacific Prairie (279).
Original vegetation included cool-season perennial bunchgrasses, annual and perennial grasses, and forbs. Now it is mostly dominated by weedy annuals, and annual forbs (279).
Land has been cultivated for ranching/farming, urbanized/industrialized, and introduced to Invasive Plant Communities (279).

Desert Grasslands:

This arid environment extends from Shortgrass Prairie in Texas and New Mexico, South to Northern Mexico (280).
Three types of Mesquite have increased on all soil types (280).
Have been modified for such a long time, that no standard for comparison exists (280).
Grazing has influenced fluctuations between grassland and shrubland ecosystems (280).

The Great Plains

Physical characteristics:

Precipitation and temperature are the most important variables (Lauenroth 229).
Annual precipitation from 300 mm in the West to 1000 mm in the East; seasonality and amount as snowfall varies, winter is the dry season (229).
Mean annual temperatures range from 2 (in the North) to 18 (in the South) degrees Celsius (231).
Mostly dry sub-humid or semi-arid environment, less than 1% arid (233)
60% of the region has been converted to agricultural ecosystems (233).

Ecological characteristics

Physical characteristics of the region influence large-scale changes and variability in vegetation
Soil texture influences vegetation type, net primary production, SOM, nutrient availability, and land use (233).
West to East Precipitation gradient influences shortgrass growth in the West and Tallgrass growth in the East (235).
Precipitation and Temperature gradient result in changes in composition of C3 and C4 grasses; where C3 dominates colder drier regions, and C4 is more abundant in warm, humid areas (235)
“The multidimensional gradients in climate, soil and plant-type gradients across the central grassland region result in a complex spatial distribution of potential plant communities” (237)
Arrival of European settlers resulted in the introduction of exotic plants; leading to a reduction of native vegetation and an increase in Invasive plant communities (247).
Most of the area has been converted to cropland, in areas where precipitation, temperature, and soil make land the most suitable for farming; leading to loss of native vegetation, net primary production, and changes in balances of nitrogen and carbon (247).
Disturbance could be fire, drought, human activity, invasive plants, grazing, etc.
Habitat and food source for livestock and wildlife

Important Grass Species
Big Bluestem:
family- Poaceae
Scientific Name- Andropogan gerardii
Origin- Native
Lifespan- Perennial
warm season grass
deep roots, rhizomes in top 10 cm
climax species
forage for sheep, horse, cattle, elk, deer, pronghorn. Preferred by livestock over most other grass species. Birds may eat seeds.
Essential cover for birds and small mammals, highly nutritious and palatable.
Shade tolerant, tolerates moderate grazing.
Family- Poaceae
Scientific Name- Sorghastrum nutans
Native Perennial
1-2 meters tall, warm season grass, scaly rhizomes, germinates from seed
climax species but can also invade disturbed sites
Eaten by livestock and wildlife in the summer. Seeds eaten by small mammals. Excellent cover for certain birds.
Moderately tolerant of salinity and acidity.

I think these two species of Tallgrass are some of the most important in the Great Plains because they both serve as a food source for livestock and wildlife, habitat for wildlife, and possess important adaptations. They are also both considered a climax species, and will dominate an undisturbed ecosystem.

One of the things that makes The Great Plains so important is the vast land area it covers in the United States. It has a broad and variable range of precipitation, temperature, and soil that produces a unique ecosystem. The vegetation provides valuable forage for livestock and forage/cover for wildlife.This landscape also provides great topography for agriculture, farming, and ranching; contributing to the economic productivity of the United States. The grassland ecosystem influences nutrient cycling, water quality and quantity, and other ecosystem goods and services. The Great Plains are greatly threatened by anthropological activity (agriculture, urbanization, energy development), overgrazing, fire (suppression), drought, and invasive plants. Unsustainable use of the Great Plains leads to degradation and a threatened status.

Luaenroth, W. K.; Burke, I .C.; and Gutmann, M. P., “The Structure and Function of Ecosystems in the Central North American Grassland Region” (1999). Great Plains Research: A Journal of Natural and Social Sciences. Paper 454.

Sims, Phillip L., “Ch 9: Grasslands” North American Terrestrial Vegetation. Cambridge University Press. 1999.

C3 Plant Metabolism vs. C4 Metabolism

Photochemical reactions of photosynthesis are the light reactions of plants. The chemical equation is 2 H2O + 2 NADP+ +2 ADP + 2 PI – 2 NADPH2 + 2 ATP + O2. Special adaptations plants have evolved include extended and broad, lateral leaves that absorb more radiation for photosynthesis. The organelle responsible for photosynthesis is the Chloroplast. The chloroplasts contain many different pigments that allow for light absorption. Chlorophyll is a main pigment and stable molecule that has the ability to gain and lose electrons; therefore able to pass on excited electrons to other molecules. Photochemical reactions occur in the Thylakoids and Thylakoid Membrane. 3 things occur in excited pigments: energy is transferred to a reaction center, heat is produced and energy is lost, fluorescence releases photons and energy is lost.

The Enzymatic reactions of photosynthesis are processes that involve the dark reactions and do not require light. These processes take place in the stroma, aqueous medium. Photorespiration in the Glycolate pathway is an inefficient process that increases in hot temperature and low humidity climates and: fixes O2 instead of CO2, a major disadvantage of C3 photosynthesis.
NADPH and ATP are important in both types of photosynthesis because they are the energy that combine with carbon dioxide and water to produce glucose and oxygen. Photosynthesis= 6 CO2 + 6 H2O + energy -> C6H12O6 + 6 O2. Photosynthesis is a biological process in which solar energy is used to form chemical bonds. Photosynthesis is important for many reasons including oxygen evolving photosynthesis producing and regulating atmospheric oxygen for respiration and forming the ozone layer, protecting Earth from UV radiation.

The main differences between C3 and C4 grasses:
C3 Metabolism:
used by all plants,
the most prevalent and primitive pathway,
evolved with climates of high CO2 and low O2
C4 Metabolism:
PEPcase Phosphoenolopyruvate carboxylase (higher affinity for CO2 and none for O2) is the initial receptor of CO2 instead of Rubisco,
occurs in Mesophyll cells and Bundle Sheath cells (contain chloroplasts) surrounding the Xylem and Phloem (veins),
is an adaptation that solves the problem of photorespiration,
evolved 7-9 million years ago in a period with high O2 concentration

C3 and C4 grasses are highly linked to different environments because of different advantages/disadvantages the C3 and C4 photosynthesis/pathways evolved. The advantages of C4 Photosynthesis include no photorespiration, CO2 fixation is resistant to heat and drought, higher water use efficiency. Disadvantages include cold sensitivity (therefore evolving to be warm season plants); and contain more bundle sheath cells (high in fiber)/less mesophyll so are more fibrous than C3 grasses. Photosynthesis relies on Rubisco to fix CO2; factors affecting Carboxylation (acquisition of CO2 by Rubisco) include Rubisco quantity/activity, CO2 concentration, acceptor concentration (RuBP), protoplasm hydration, temperature, and minerals (P). Since C4 is reliant on PEPcase as an initial receptor and not Rubisco, it evolved to reduce photorespiration before carboxylation occurs. C3 pathway evolved during a time in history where the atmosphere was high in CO2, low in O2; while C4 pathway evolved during a period that the atmosphere was high in O2. So climatic conditions influence what environments C3 and C4 grasses grow in. Areas with higher O2 concentration will have more C4 grasses because of their adaptation to photorespiration (a disadvantage of C3 photosynthesis), in hot and humid environments. The C3 pathway is more evolutionarily ancient because it speciated before the C4 pathway. The C4 evolved this adaptation due to natural selection making them more fit for environments the C3 grasses can not survive in.

Rangeland- Grasslands

Rangelands are arid and semiarid wildlands that make up to 60% of the world’s land mass; composed of native vegetation of grasslands, shrublands, and open woodlands. For various reasons (low precipitation, rough topography, cold temperatures, etc) Rangelands are unsuitable to grow timber and crops. Rangelands provide multiple ecosystem goods and services such as grazing for livestock and habitat for wildlife, serving as a watershed, improving soil and water quality, providing clean air, open spaces, and recreation.
Grasslands can be defined as land composed mostly of grass species, members of the family Poaceae, with little or no woody vegetation. Sufficient precipitation is needed to be able to support grasses, but not trees and shrubs, in this biome. Grasslands occur on every continent and are around 23% of total land cover.
Grasslands are important economically because of grains from cereal grasses that provide food for animals and humans: wheat, rice, corn, oats, barley, rye. Grasses also provide hay and pasture for livestock. Grasses are important ecologically because they have an extensive root system that improves soil quality and prevents erosion. They also influence sequestration of CO2. They are worth studying because of the ecosystem goods and services grasses provide.

Grasslands are threatened by a variety of human activities including agriculture, fragmentation, invasive species, lack of fire, desertification, urbanization, and livestock. Grasses are being converted to cropland and infrastructure, suppressed of fire, and overgrazed by different animals. All of these things contribute to the loss and degradation of grasslands. It is important to conserve grasslands because of the regulating, provisioning, and cultural services that they provide. Grasslands provide food and habitat, improve soil and water quality, play a role in nutrient cycling, and have cultural value. It is important that we manage grasslands sustainably so that these goods and services continue.

E.O Wilson identified two laws in biological/ecological systems: properties of life are obedient to laws of chemistry and physics, and all biological processes and differences that distinguish species are evolved from natural selection. Species originate from the evolution of some difference that adapts them to the environment. Natural selection is the process by which organisms that have physical/molecular traits that better adapt them to their environment will tend to survive and reproduce. Speciation is the formation of new and distinct species, from the splitting of one evolutionary lineage into two. Natural selection is the primary influence driving evolution, and therefore speciation.
Grasses are in the division Magnoliophyta, class Liliopsida, in the order Cyperales, part of the family Poaceae (Gramineae), have 600 genera, and have around 9000 species. They occur in arid or semi-arid environments. They are annual (reestablish by seed each year) or perennial (persist from year to year) herbs that have noded stems. The have leaves with two parts: sheath surrounding stem and a linear, flat blade. Flowers are formed by inflorescence subdividing into spikelets, which other flowering plants do not have. The dry fruit is called caryopsis (grain). Grasses have rhizomes, stolons, basal leaf meristems, high shoot/root density, underground nutrient reserves, deciduous roots, and rapid transformation/growth.
The main adaptations of grasses involve responses to the disturbance of drought and open space. They have evolved to be wind pollinated and drought resistant. Grasses are able to spread during periods of increasing drought because of traits such as Basal meristems, small stature, high root and shoot density, deciduous roots, underground nutrient reserves, and rapid transformation and growth. Rhizomes and Stolons are used as growth strategies to extend the root system laterally. Other adaptations include how rhizomes evolved because of trampling by large herbivores, basal leaf meristems evolved as an adaptation to grazing, and wind pollination evolved due to open conditions of savannas.

Grasslands are abundant because of the genetic traits that have evolved that help them better fit their environment, to survive and reproduce. Therefore, natural selection has influenced Poaceae to survive throughout history due to specific beneficial differences evolving in response to disturbance and environmental change, and thrive in today’s biosphere. The specific traits that grasses have evolved through natural selection is basal leaf meristems, high root/shoot density, underground nutrient reserves, deciduous roots, and rapid transformation/growth, rhizomes and stolons. All of these characteristics contribute to drought resistance. As an adaptation of moving from woodland to open landscapes, grasses evolved to be wind pollinated and can reproduce more efficiently. Rhizomes and stolons produce lateral growth without the use of seeds, increasing distribution and abundance. The morphology of grasses is important to grassland abundance because without the evolutionary process forming this vegetation type, Poaceae would have never developed traits that help them better adapt to their changing environment; and they would eventually go extinct. Basically, the current state of grass species morphology is produced by species adaptation to environmental change. Overall, grasslands are abundant because of their resistance and resilience to environmental change; because of their ability to easily adapt to disturbance because of traits they evolved due to natural selection and speciation.

Changing Human Behavior to Minimize/Mitigate Disturbance

One major aspect of changing human behavior to minimize and mitigate disturbance is through education and awareness. In the case of invasive species, informing people about the consequences of transporting plants and animals to new places will mitigate the spread of invasive species. For fire disturbance, educating people on the dangers of fire suppression as well as how fires benefit an ecosystem may influence greater acceptance and better management. Grazing can be better managed by the knowledge and use of Grazing Systems. Governmental policy is also effective in changing societal behavior, for example a carbon tax can minimize the human impact on climate change by limiting emissions. In order to change individual human worldviews, educated discussion and supported facts go a long way to convince people to consider ideas that they haven’t before.

The Human Footprint is an important factor influencing management methods. Disturbance is greatly impacted by human urbanization, and can be better managed if we understand the relationship between human activity and the effects of disturbance on different ecosystems. Research on the Human Footprint helps to minimize and mitigate disturbance, and has developed as “humans have dramatically altered wildlands in the western United States over the past 100 years by using these lands and the resources they provide. Anthropogenic changes to the landscape, such as urban expansion and development of rural areas, influence the number and kinds of plants and wildlife that remain. In addition, western ecosystems are also affected by roads, powerlines, and other networks and land uses necessary to maintain human populations. The cumulative impacts of human presence and actions on a landscape are called the “human footprint.” These impacts may affect plants and wildlife by increasing the number of synanthropic (species that benefit from human activities) bird and mammal predators and facilitating their movements through the landscape or by creating unsuitable habitats. These actions can impact plants and wildlife to such an extent that the persistence of populations or entire species is questionable…The human footprint aids managers in planning, implementing land-use actions, and developing strategies to conserve habitats and wildlife. Modeling the human footprint across large landscapes also allows researchers to generate hypotheses about ecosystem change and to conduct studies in regions differing in potential impact. Because funding for restoration and conservation projects is limited, and because there is little room for errors in the management of species of concern, land managers are able to maximize restoration and conservation efforts in areas minimally influenced by the human footprint. As such, the human footprint model is an important first step toward understanding the synergistic effects acting on shrublands in the western United States.” (USGS). The Human Footprint measures the negative or positive changes that humans have made to a landscape. It includes factors of urbanization, recreation, Energy development, and climate change. All of these things are valuable or inevitable, but educated management can help make these things sustainable. Considering the areas least impacted by the human footprint allows managers to consider what ecosystem is worth the time, money, and effort to repair and research.


USGS. The Human Footprint in the West: A Large-scale Analysis of Human Impacts. US Department of the Interior. December 2003.

Salmon Without Rivers Discussion

Lichatowich, Jim. Salmon without Rivers: a History of the Pacific Salmon Crisis. Island Press, 1999.

In Chapter 7 of Salmon Without Rivers, Lichatowich discusses solutions to the four main problems causing the declining abundance of salmon: facilitating salmon egg transfer, eliminating predators of salmon, controlling ocean troll fishery, and strengthening salmon passage at high dams (pg 152). In 1925, experts met in Seattle; finally acknowledging and discussing the extent of these issues, and how to solve them. One conclusion that came from the meeting was that substantial research of salmon and their decline was still needed (proposed by Gilbert). Considered by some to be the first fisheries biologist in the US, “as early as 1913, Gilbert had used an ingenious method to work out the basic life histories of the Pacific Salmon…The salmons scales grow roughly in proportion to the growth of the fish, and as the scales grow, circular ridges are deposited on their surface. These rings, called circuli, are similar to the rings in a cross sectional cut of a tree. Narrow spacing between tree rings means slow growth, whereas wide spacing indicates rapid growth” (pg 164). This methodology still influences current knowledge of salmon life history, for example, from Gilbert’s idea of dividing “juvenile salmon into two general categories, stream and ocean, based on their life histories. Stream-type fish remained in fresh water for a year and migrated to sea in the spring of their second year of life. Ocean-type fish migrated to sea shortly after emerging from the gravel during their first year of life” (pg 164). As you can see, Gilbert’s findings about scales provided information that led to a topic integral to fish conservation: life history. This advancement in the knowledge of Pacific salmon life history improved harvest recommendations by expanding our understanding of issues like the homing of salmon, and when hatcheries should release them. Life history answers broad questions like, what/ when/ where/ and how salmon do things; and also very specific questions like, “that salmon populations were composed of individual fish that exploited their environment in different ways. He speculated that this life history diversity had an ecological basis, and that it was an integral part of the relationship between the fish and it’s environment” (pg 165). One issue that hatcheries (at the time) had with Gilbert’s findings was that they believed that human controlled production was more efficient than natural ecological processes (165), and therefore continued to degrade fish natural life history by operating hatcheries on their own terms. By taking a more ecological and scientific approach, harvest management can be improved. All of the problems causing the decline of salmon, introduced in the 1920’s Seattle meeting, are human caused. Researching salmon life history, and applying convergent evidence to harvest management, will likely improve salmon abundance.

Other aspects of salmon ecology that should be considered are the general changing effects that human urbanization has on salmon habitat. Examples include the effects of climate change, recreation, disturbance, and energy development. By studying and managing these things with a greater environmental ethic, humans can create greater biodiversity of salmon habitat, and provide better chances for natural ecological processes to work.

Local Invasive Species


An invasive species that I have seen in my hometown of Newberg Oregon is Nutria (Myocastor Coypus). They inhabited the forest/creek that ran through my families backyard and around our Cul-de-sac. Nutria compete with native species for food, resources, and habitat. They also cause destruction to natural landscape through burrowing.

“Nutria are native to South America and were introduced deliberately into North America for fur farming in the 1930s. In Oregon, the species is limited to areas in the southern Willamette Valley and central Coastal Region. It usually occurs in or adjacent to rivers, lakes, sloughs, marshes, ponds, and temporarily flooded fields. Nutrias construct burrows in banks of rivers, sloughs, and ponds, sometimes causing considerable erosion.” (https://myodfw.com/wildlife-viewing/species/invasive-species (Links to an external site.))

This invasion could have been prevented in multiple ways. Their transportation from South America, simply for economic benefit through fur farming, could have been prevented. Establishing hundreds of Nutria Farms in the Pacific Northwest could have been prevented. Farmers releasing Nutria when it became uneconomical, also could have been prevented. This invasion could have been prevented if the economical benefits of fur trade didn’t influence people to transport them here and establish farms.

Invasive Species-negative effects on Biodiversity

Here https://www.environmentalscience.org/invasive-species (Links to an external site.) is a page that generally describes the history, consequences, and simple management of invasive species. The issues caused by invasive species have been occurring for thousands of years; from Romans using foreign species in the Colosseum, to European colonization of the New World. Exotic plants and animals can be detrimental to an ecosystem because these species did not co-evolve with the native species of the landscape. Throughout history, invasive species have generally been introduced in three ways: 1) Accidently released in a new area they were intentionally brought to, 2) Introduced to eradicate another invasive species, 3) Sneaking into Cargo on ships.

Invasive species can be managed and controlled. One key factor is educating people about the dangers of transporting wildlife to new places. Hunting is also a way to manage uncontrolled invasive species as well. The article overall emphasizes the impact globalization has on the number of invasive species.

In my opinion, the root cause of the issues that invasive species may impose is the fact that the species did not co-evolve with the native species of the area. Ways in which one species evolved in it’s natural habitat, may not fit into the foodweb of other ecosystems. So when an invasive species thrives, it hurts the biodiversity of the natural area. Human action influences the introduction of invasive species through globalization. In Oregon, feral swine are an invasive species that “have been shown to restrict timber growth, reduce and/or remove understory vegetation and destabilize soils, causing increased erosion and compaction while simultaneously decreasing stream quality. Rooting and grubbing activities have been shown to facilitate the invasion of noxious weeds and other nonnative vegetation, reducing site diversity and distribution of native species. Feral swine compete with native wildlife and livestock for food and habitat, and they prey on young native wildlife and livestock. Feral swine can transmit disease to wildlife, livestock and humans” (ODFW Invasive Species Fact Sheet http://www.dfw.state.or.us/conservationstrategy/invasive_species/docs/ferel_swine_fact_sheet.pdf (Links to an external site.)). They were introduced by escaping from domestic swine facilities or by being released intentionally. ODFW requires landowners to inform them when there are feral pigs on their property and to submit a removal plan. They also ban the sale of hunts on public/private property. Feral pigs are so prolific that even with legal hunting, the invasive population only increases. Management plans are complex for this reason. I think that it will take a combination of educating people on not releasing their pigs/keeping their domestic pigs secure, eradicating feral pigs, and taking precautionary measures for agriculture and livestock to make a good attempt at controlling this invasive species. It takes correcting negative human action to help control the future biodiversity of ecosystems.