ENVIRONMENTAL SCIENCE
9/20: Chapter 5 - Biomes
Terrestrial Biomes
A biome is an area that shares similar climate, topographic, and soil conditions, as well as basic types of biological communities (plants and animals).
Temperature and precipitation are among the most important determinants in biome distribution.
Temp-controlled biomes occur in latitudinal/east-west bands.
Biomes can be predicted off of average temperature and annual precipitation.
Warmer biomes (like tropical forests) exist near the equator, for example.
Temperature and precipitation also change with altitude.
Vertical zonation — applied to vegetation zones defined by altitude.
Tropical Rainforests
Humid regions in the tropics that support one of the most complex and biologically rich biomes. Includes ample rainfall and uniform temperatures.
Cloud Forests are defined by high mountains where fog and mist keep vegetation continually wet.
Conditions occur when rainfall exceeds 200cm (80in) per year and temperatures remain warm/hot year-round.
Rainforest soil is thin, acidic, and poor in nutrients.
Nutrients experience rapid decomposition and cycling.
90% of nutrients “ties up” into living organisms.
Soil cannot support cropping or resist erosion.
½ - 2/3 of all species of terrestrial plants/animals live in tropical forests.
Tropical Seasonal Forests
Tropical regions that have wet and dry seasons with hot temperatures year-round, containing brown and dormant foliage for much of the year but becomes green during the rainy season.
Many of the plants are drought deciduous, so they lose their leaves when it’s dry.
Soil here is richer and more productive land for agriculture.
Easy land to settle in the dry season → humans burn away the land when its dry so that it is ready for settlement.
Tropical Savannas and Grasslands
Grasslands with sparse tree cover and little rainfall amounts. Prone to fire due to dry seasons.
Plants and animals have adapted to the dry conditions. Plants have long roots and many animals are migratory.
Deserts
Characterized by low moisture levels and precipitation that is infrequent and unpredictable. Wide daily and seasonal temperature fluctuations are also common.
Plants exhibit water conservation characteristics and only set seed after spring rains.
Many animals are nocturnal and conserve water to adapt to these conditions.
Deserts are vulnerable due to slow-growing vegetation and overgrazing.
Can be hot or cold deserts.
Temperate Grasslands
Communities of grasses and seasonal herbaceous flowering plants (forbs). Few trees and large daily/seasonal temperatures.
Thick, nutrient-rich organic soils that are perfect for farmlands.
Overgrazing is a major threat.
Temperate Shrublands
Warm, dry summers and cool, moist winters that occur in the Mediterranean regions.
Evergreen shrubs, pines, and scrub oaks.
Fires are a major factor.
Referred to as a chaparral in California, home to a high number of unique species.
Temperate Deciduous Forests
Supports lush summer plant growth when water is plentiful.
Deciduous trees lose their leaves in winter as an adaptation to freezing temperatures.
These areas were harvested heavily in the early settlement days of the U.S. for timber and are subjected to deforestation nowadays as well.
Temperate Rainforest
A cool, rainy forest often enshrouded in fog. Mild temperatures occur year-round with abundant rainfall.
Coniferous forests mainly.
Boreal Forests
Broad band of mixed coniferous/deciduous trees (50 degrees and 60 degrees N latitude).
Pines, hemlock, spruce, cedar, fir, etc.
Extremely cold and short summers that limit the growth rate of trees.
A taiga is the northernmost edge of the boreal forest.
Tundra
A treeless landscape that occurs at high latitudes or on mountaintops.
Growing season of 2-3 months.
No trees, limited water.
Arctic → low productivity, long winters, permafrost.
Alpine → near mountaintops, short intense growing season.
Marine Ecosystems
Oceans cover 70-75% of Earth’s surface.
Photosynthesis is carried out by algae or phytoplankton, occurring mostly near the coast.
Biological Productivity
Areas of ocean that are open and deep are biologically impoverished, with ocean areas nearer to land possessing higher biological activity.
Vertical Stratification is a key feature in marine ecosystems.
Light and temperature decrease with depth and deep ocean species often grow slowly.
Cold water has more O2 than warm water, so productivity is often higher.
Ocean System Classifications
Benthic → bottom
Pelagic → water column above the bottom.
Multiple zones: epipelagic, mesopelagic, bathypelagic, abyssopelagic, and hadalpelagic.
Littoral → near the shore.
Thermal Vent Communities
Hold great diversity.
Rely on chemosynthesis.
Comprised of tube worms, mussels, and microbes that have adapted to survive the extreme temps and intense water pressures.
Coastal Zones
Communities vary with depth, light, temperature, and nutrient concentration.
Coral reefs: aggregations of coral polyps that live symbiotically with algae, found in warm and shallow water, threatened by trash, sewage, urbanization, global warming, etc.
Mangroves: trees that grow in saltwater along tropical coastlines, helps stabilize shorelines, serves as nurseries for fish/shrimp, threatened by deforestation.
Estuaries: bays/semi-enclosed bodies of brackish water that form where rivers enter the ocean.
Salt marshes: coastal wetlands flooded by seawater, nutrient/biologically diverse, threatened by sewage.
Tide pools: depressions in rocky shorelines that are flooded at high tide but retain water at low tide, preventing plant growth but promoting animal communities, as well as diverse growth in harsh conditions.
Barrier islands: narrow islands of sad that form parallel to a coastline, providing protection from storms/waves/tides, threatened by storm erosion.
Freshwater Ecosystems
Lakes
Distinct vertical zones:
Epilimnion → warm upper layer.
Hypolimnion → cold, deeper layer that does not mix.
Thermocline → distinctive temperature transition zone that separates warm upper layers and deeper colder layers.
Benthos → bottom.
Wetlands
Land surface is saturated or covered with water for at least part of the year.
Swamps → wetlands with trees.
Marshes → wetlands without trees.
Bogs/Fens → waterlogged soils, nutrient poor.
Shallow water, so high productivity still.
Traps and filters water + stores water runoff.
Conservation is important due to rich biodiversity (bird species are common here).
Human Disturbance
Humans prevent about 40% of net terrestrial primary productivity.
Conversion of habitat → human use is the single largest cause of biodiversity loss.
Small systems are at the most risk.
Many biomes are so delicate that any small change can put it in danger.
Agricultural practices.
Deforestation.
Habitat destruction.
Global climate change.
Pollution.
9/27: Chapter 6 & 7 - Population Biology and Human Populations
Population Biology → the science of modeling changes in species abundance.
Ex. Bluefin tuna can live for 50 years, but they mature slowly.
Mathematic Population Growth
Geometric Rate of Increase or Geometric Growth
The population size that would occur after a certain amount of time under ideal conditions is described by:
Nt=N0rt
N = population, r = rate, t = time.
Exponential Growth
Continuous change and growth.
dN / dt = rN
d = delta (change) → “The change in the population (dN) per change in time (dt) is equal to the rate of change (r) times the population size (N).
Can only be maintained by a population as long as nothing limits its growth.
Population Terminology
Carrying Capacity (K) - the population of a species that can be supported in a specific area without depleting the available resources.
Overshoot - when a population exceeds the carrying capacity of the environment and deaths result from a scarcity of resources.
Population crash - a rapid dieback in the population to a level below the carrying capacity.
Boom and bust - when a population undergoes repeated cycles of overshoots followed by crashes.
Resource Scarcity
Population growth slows down as resources become scarce and a population nears its carrying capacity.
Shown in an “s-shaped” or sigmoidal growth curve.
Logistic growth → dN / dt = rN (1 - N / K) → proportion of carrying capacity.
Factors Affecting Population Growth
Logistic growth is density-dependent, meaning growth rate depends on population density.
Disease, physiological stress, and predation can influence a population.
Density dependent vs independent.
Dependent → intensifies as population increases.
Independent → includes drought, fire, or habitat destruction that affects an ecosystem.
r and K selected Species
r-selected
relies on high reproductive rates to overcome high mortality of offspring, extrinsically affected, low trophic level.
K-selected
have few offspring, slower growth, and more parental care, intrinsically affected, high trophic level.
Factors that Affect Growth Rates
Births → number of births that occur in the population.
Immigration → the number of organisms that move into the population from another.
Deaths → mortality, or number of deaths that occur in the population.
Emigration → the number of organisms that move out of the population to another.
r = B + I - D - E.
Life Span
Varies by species.
Maximum life span refers to the longest period of life reached by a given type of organism.
Differences in relative longevity among species are shown as survivorship curves.
Three Patterns
Full physiological lifespan
Probability of death unrelated to age
Mortality peaks early in life
Factors that Regulate Population Growth
Intrinsic factors → same species
Extrinsic factors → outside of a species population
Biotic factors → caused by living organisms; density dependent.
Reduces population size by decreasing natality or increasing mortality.
Interspecific interactions.
Predator-prey oscillations.
Intraspecific interactions involve competition for resources by individuals within a population.
Abiotic factors → caused by non-living environmental components; density independent.
Island Biogeography
Conservation Genetics
In a large population, genetic diversity tends to be preserved. In small populations, small events can affect the gene pool (genetic drift).
Founder Effect → occurs when few individuals start a new population.
Demographic Bottleneck → occurs when a few members of a species survive a catastrophic event.
Population Viability Analysis
Minimum viable population is the minimum population size required for long-term species survival.
Metapopulations
Connected populations that have regular or intermittent gene flow between geographically separate units.
Source habitat → birth rates are higher than death rates. Surplus migrates to new locations.
Sink habitat → birth rates are less than death rates. Species can disappear if not replenished.
Perspectives on Population Growth
Ways We Describe Growth
Fertility and Morality
Life Span and Life Expectancy
Factors that Affect Population Growth
Future of Growth