Ecosystems and Biodiversity Notes

The Living World: Ecosystems

Introduction to Ecosystems

  • Interactions between living organisms and their physical environment define an ecosystem.
  • Biotic Factors: Living components, e.g., plants, animals, microorganisms, fungi, protists.
  • Abiotic Factors: Nonliving (physical) components, e.g., hydrosphere, atmosphere, geosphere; nutrients, pH, salinity, dissolved oxygen (DO), wind speed, temperature, depth.
  • Biosphere: The region of Earth where life exists, encompassing all ecosystems.
  • Ecosystem: A community of living organisms and their physical environment in a specific area.
  • Ecosystems can have distinct boundaries (e.g., caves, lakes).
  • Most ecosystems have indistinct boundaries, making it hard to determine where one ends and another begins.
  • Ecosystems interact with their surroundings through energy and matter exchange.
  • Competition: The struggle of individuals to obtain limited shared resources.
  • Competitive Exclusion Principle: Two species competing for the same limiting resource cannot coexist.
  • If two species share the same realized niche, the superior competitor will drive the other to extinction.

Competition and Resource Partitioning

  • Competition for limiting resources impacts population sizes.
  • Gause's experiments with Paramecium:
    • P. aurelia and P. caudatum grew well separately.
    • When grown together, P. aurelia thrived, while P. caudatum went extinct, demonstrating the competitive exclusion principle.
  • Resource Partitioning: Species divide a resource based on behavioral or morphological differences.
    • Selection favors individuals that minimize resource overlap with other species.
    • Over generations, species evolve to reduce overlap and partition resource use.

Species Interactions

  • Mutualism: Interaction between two species that benefits both by increasing their survival or reproduction chances.
    • Example: Acacia trees and ants – trees provide food and shelter to ants, while ants protect trees from herbivores and competitors.
    • Coral reefs and algae – coral provides home, algae provide sugars via photosynthesis.
    • Lichens (alga + fungus) – fungus provides nutrients to alga, alga provides carbohydrates via photosynthesis.
  • Predation: One animal kills and consumes another.
    • Prey species evolve defenses to avoid predators.
  • Parasitism: One organism lives on or in another (host).
    • Parasites rarely kill hosts directly.
    • Pathogen: A parasite that causes disease in its host.
    • Parasitoid: Predator that lays eggs inside a host organism.
  • Herbivory: An animal consumes plants or algae.
    • Abundant herbivores can significantly impact producer populations.
    • Producers evolve defenses (e.g., spines, distasteful chemicals) against herbivores.
  • Commensalism: One species benefits, while the other is neither harmed nor helped.
    • Example: Birds perching on a tree to spot food; the tree is unaffected.

Species Distribution and Impact

  • Native Species: Species living within their historical range for thousands or millions of years.
  • Exotic (Alien) Species: Species living outside their historical range.
    • Example: Honeybees introduced to North America in the 1600s; red foxes introduced to Australia for hunting.
  • Accidental introductions:
    • Rats on cargo ships reaching oceanic islands.
    • Fungi wiping out American Elm and Chestnut trees in the U.S.
  • Many exotic species fail to thrive in new regions.
  • Invasive Species: Exotic species that thrive and cause harm to native species.
    • Examples in the U.S.: rats, zebra mussels, kudzu.

Terrestrial and Aquatic Biomes

  • Biomes: Categorized by average annual temperature and precipitation.
    • Examples: Tropical rainforest, tropical seasonal forest, subtropical desert, woodland/shrubland, temperate grassland, temperate seasonal forest, temperate rainforest, boreal forest, tundra, polar ice cap.
  • Terrestrial Biome: Geographic region defined by average annual temperature, precipitation, and plant growth forms on land.
  • Plants and animals adapt to the specific climate of a biome.
  • Aquatic Biome: Aquatic region defined by salinity, depth, and water flow.
  • Climate diagrams display monthly temperature and precipitation, indicating biome productivity.

Aquatic Biomes: Freshwater

  • Freshwater biomes include streams, rivers, lakes, ponds, and freshwater wetlands.
  • Often serve as sources of drinking water.
  • Rivers: High oxygen levels due to flowing water; carry nutrient-rich sediment to deltas and floodplains.
    • Flowing fresh water from underground springs or runoff from rain/snow.
    • Streams are narrow with small water volume; rivers are wider with larger water volume.
  • Lakes and ponds: Standing water, often too deep for emergent vegetation.
    • Littoral zone: Shallow water with rooted plants.
    • Limnetic zone: Deeper water where plants don't emerge.
    • Profundal zone: Deepest water with limited light and oxygen.
    • Benthic zone: Sediments at the bottom of all three zones.
  • Lakes are classified by fertility level:
    • Oligotrophic: Low nutrients, low phytoplankton, clear water.
    • Mesotrophic: Moderate fertility level.
    • Eutrophic: High fertility, turbid water, high algae growth often due to human-introduced fertilizers.
  • Freshwater wetland: Area submerged/saturated by water for part of the year, supports emergent vegetation.
    • Among the most productive biomes on Earth.
    • Benefits: Flood control, groundwater recharge, water filtration, high plant growth.

Biogeochemical Cycles

  • Biogeochemical cycle: The movement of matter within and between ecosystems.
  • Energy flows, and matter cycles.

The Carbon Cycle

  • Movement of matter between sources and sinks.
  • Source: Releases more greenhouse gas into the atmosphere than it absorbs.
  • Sink: Reservoir that absorbs and holds a chemical element or compound for a long time.
  • 7 processes of the carbon cycle:
    • Photosynthesis, respiration, exchange, sedimentation, burial, extraction, and combustion.
  • Fast parts: Living organisms, exchange of CO_2 between air and water, combustion of organic carbon.
  • Slow parts: Carbon held in rocks, soils, and fossil fuels for millions of years.
  • Reservoir: Stores carbon or other substances; can be sources or sinks.
  • Largest carbon reservoir: rocks/sediments in the ocean.

Carbon Cycle Processes

  • Photosynthesis:
    • Plants, algae, phytoplankton remove CO_2 from atmosphere and convert it to glucose.
    • Acts as a CO_2 sink.
  • Cellular Respiration:
    • Plants, animals release stored energy, use O_2 to break down glucose, and release energy.
    • Acts as a CO_2 source.
  • Ocean and Atmosphere:
    • CO_2 moves directly between ocean and atmosphere.
    • Dissolves into and out of ocean water at the surface, maintaining balance.
    • More CO_2 leads to ocean acidification.
  • Sedimentation:
    • Marine organisms take out CO_2 to make calcium carbonate exoskeletons.
    • Dead organisms sink, and their bodies break down into sediments with Carbon.
  • Burial:
    • Over time, pressure changes turn sediments into sedimentary stone (e.g., limestone, sandstone), creating long-term Carbon reservoir.
  • Extraction and Combustion:
    • Extraction of fossil fuels by humans, followed by combustion (burning), releases carbon into the atmosphere.

Human Impacts on the Carbon Cycle

  • The cycle is balanced without human influence.
  • Combustion of CO_2 is leading to global warming.
  • Greenhouse gases absorb heat.
  • CO_2 contributes the most to warming.
  • Humans are moving fossilized carbon to the atmosphere faster than sedimentation and burial, upsetting the balance.
  • Tree harvesting increases CO_2 in atmosphere.
  • CO_2 levels have increased from 280 ppm in 1800 to over 420 ppm today.

The Nitrogen Cycle

  • Moves nitrogen from the atmosphere into soils via fixation pathways, including fertilizer production.
  • Nitrogen can exist in several forms in the soil.
  • Denitrifying bacteria release nitrogen gas back into the atmosphere.
  • Atmosphere is a major reservoir of nitrogen.
  • Critical plant and animal nutrient for DNA and protein synthesis.
  • Nitrogen fixation: Converts nitrogen gas (N2) into usable forms (ammonium NH4^+ and nitrate NO_3^-).
  • Available for plant uptake and incorporation into tissue.
    *

Nitrogen Cycle Processes

  • Bacteria Fixation:
    • Bacteria in soil or symbiotic relationship with root nodules convert N_2 into ammonia.
    • Involves cyanobacteria and bacteria in legume roots.
  • Synthetic Fixation:
    • Humans burn fossil fuels to convert N2 into NO3.
    • Nitrates are added to fertilizers.
  • Nitrification:
    • Conversion of NH4^+ into nitrite NO2^- and then nitrate NO_3^- by soil bacteria.
  • Assimilation:
    • Plants take in nitrates and ammonia from soil.
    • Animals eat plants and other animals to obtain nitrogen.
  • Ammonification:
    • Fungal and bacterial decomposers break down organic nitrogen in dead bodies/waste into ammonia.
  • Denitrification:
    • Conversion of nitrate NO3^- into nitrous oxide (N2O) and nitrogen gas (N_2) under anaerobic conditions.

Human Impacts on the Nitrogen Cycle

  • Climate: Nitrous oxide (N_2O) is a greenhouse gas, contributing to warmer climate.
  • Ammonia volatilization: Excess fertilizer leads to NH_3 entering the atmosphere, causing acid precipitation and respiratory irritation.
  • Leaching and Eutrophication: Synthetic fertilizers cause nitrates (NO_3^-) to leach from soil into waterways, leading to algae blooms.

The Phosphorus Cycle

  • Begins with weathering or mining of phosphate rocks and the use of phosphate fertilizer.
  • Releases phosphorus into the soil and water.
  • Used by producers and moves through the food web.
  • In water, phosphorus can precipitate and form sediments, eventually becoming phosphate rocks.
  • Major reservoirs: rocks and sediments with phosphorus-bearing minerals.
  • No atmospheric component.
  • Limited transfer from ocean to land.
  • Scarce in aquatic and terrestrial biomes.
  • Phosphorus is a limiting factor in undisturbed ecosystems.
  • Very slow cycle.

Human Impacts on the Phosphorous Cycle

  • Humans mine phosphorus to make fertilizer.
  • Fertilizer runoff leads to phosphorus leaching into water bodies, causing algae growth.
  • Algal Bloom: Rapid increase in algae, some of which produce toxins.
  • Algae die, and decomposition consumes oxygen, creating hypoxic conditions.
  • Dead Zone: Low oxygen levels lead to fish and aquatic organism deaths.
    • Example: Mississippi River into the Gulf of Mexico.
  • Phosphates in detergents also contribute; now banned in detergents in some regions.

The Hydrologic (Water) Cycle

  • Movement of water between sources and sinks in different states (solid, liquid, gas).
  • Driven by solar energy.
  • Ocean is the largest reservoir.
  • Ice caps and groundwater are smaller reservoirs with usable freshwater.
  • Transpiration: Plants draw groundwater from roots to leaves, where it evaporates through stomata.
  • Evapotranspiration: Combined evaporation and transpiration.
  • Precipitation pathways:
    • Runoff: flows over the surface to a body of water
    • Infiltration: trickles through soil into groundwater aquifer
  • Groundwater (aquifers) and surface water (lakes/rivers) are freshwater sources for humans and animals.
  • Precipitation recharges groundwater if soil is permeable, and recharge surface water via runoff.
  • Most sulfur exists as rocks.
  • Weathering releases sulfate ions (SO_4^{2-}) that producers assimilate.
  • Sulfur moves through the food web.
  • Volcanoes, burning fossil fuels, and copper mining release sulfur dioxide (SO_2) into the atmosphere.
  • SO2 combines with water to form sulfuric acid (H2SO_4), which returns to Earth via rain or snow.

Primary Productivity

  • Photosynthesis: Plants, algae, and bacteria use solar energy to produce sugars from carbon dioxide and water.
  • Cellular respiration: Cells unlock energy through:
    • Aerobic respiration: Glucose and oxygen are converted into energy, carbon dioxide, and water.
    • Anaerobic respiration: Glucose is converted into energy without oxygen (less efficient).
  • Primary productivity: Rate of converting solar energy into organic compounds.
    • Gross primary productivity (GPP): Total solar energy captured by producers via photosynthesis.
    • Net primary productivity (NPP): Energy captured by producers minus their respiration energy use.
    • Measured in energy per unit area per time (e.g., kcal/m2/year).
  • Producers capture about 1% of available solar energy via photosynthesis.
  • NPP is typically 25-50% of GPP.
  • Biomass: Total mass of living matter in an area.
  • Standing crop: Amount of biomass present in an ecosystem at a particular time.

Trophic Levels

  • 1st Law of Thermodynamics: Energy is neither created nor destroyed, only changes form.
  • 2nd Law of Thermodynamics: Usable energy decreases as you move up a food chain.
    • Matter and energy are not destroyed but change forms.
  • Ecological efficiency: Proportion of consumed energy passed from one trophic level to another.
  • Trophic pyramid: Distribution of biomass, numbers, or energy among trophic levels.
  • Ecosystems depend on continuous inflow of high-quality energy.
  • Terrestrial and marine communities flow energy from sun to producers in lowest trophic levels upward.

Energy Flow and the 10% Rule

  • About 10% of energy moves from one trophic level to the next; the other 90% is used or lost as heat.
  • Graphing individuals or biomass within each trophic level typically forms a pyramid.

Food Chains and Food Webs

  • Food Chain: Linear diagram linking producers and consumers, showing energy and matter movement through trophic levels.
  • Food Web: Interlocking pattern of food chains showing energy and nutrient flow.
  • Feedbacks: Occur throughout the environment.
  • Negative Feedback Loop: System responds to change by returning to its original state.
  • Positive Feedback Loop: Change in a system is amplified.
    • Example: Population growth.
  • Keystone species: Species significantly influencing community structure.
    • Examples: Sea otter, lion, gray wolf, sea star, elephant.
  • Indicator species: Plant or animal indicating ecosystem character or quality.
    • Examples: Amphibians, fish, grizzly bears, prairie dogs.
  • Ecosystem engineer: Keystone species creating/maintaining habitat.
    • Examples: Beavers, elephants, earthworms.

The Living World: Biodiversity

Introduction to Biodiversity

  • Number of species in a place measures biodiversity.
  • Estimating total species on Earth is challenging.
  • Approximately 2 million species have been named.
  • Biodiversity: Variety of life forms in an environment. Levels of biodiversity:
    • Ecosystem diversity: Variety of ecosystems in a region.
    • Species diversity: Variety of species within an ecosystem.
    • Genetic diversity: Variety of genes among individuals within a species.

Habitat and Niche

  • Habitat diversity: Variety of habitats in an ecosystem.
  • Specialists: Organisms living under a narrow range of conditions.
    • Koala eats only eucalyptus leaves.
  • Generalists: Organisms living under a wide range of conditions.
    • White-tailed deer can live in lots of places and eat lots of plants
  • Species richness (r): Total number of species in an area.
  • Higher richness indicates a healthy ecosystem.
  • Species evenness: Relative proportion of individuals within different species.
    Measures of species diversity:
    Communities can have the same species richness but different levels of species evenness.

Ecosystem Services

  • Ecosystem services: Processes by which life-supporting resources are produced.
  • Five categories of ecosystem services:
    • Provisions
    • Regulating services
    • Support systems
    • Resilience
    • Cultural services
  • Provision: A good humans can use directly.
    • Lumber, food crops, medicinal plants, natural rubber, and furs.
    • 70% of top 150 prescription drugs in the U.S. come from natural sources.
  • Regulating Services
    • Natural ecosystems regulate environmental conditions.
    • Rainforests and oceans remove carbon from the atmosphere.
    • Ecosystems regulate nutrient and hydrologic cycles.
  • Support Services
    • Natural ecosystems provide support services like pollination for food crops and natural pest control by providing habitat for predators of agricultural pests.
    • Healthy ecosystems can also filter pathogens and chemicals from the water.
    • Cultural Services
    • Awe-inspiring beauty of nature provides an aesthetic benefit that people will pay money for.
    • Scientific funding agencies may also award grants to scientists to explore biodiversity with no promise of any economic gain.
    • Ecological Tolerance
    • Resilience: rate at which an ecosystem returns to its original state after a disturbance
    • For example, several different species may perform similar functions in an ecosystem but differ in their susceptibility to disturbance. If a pollutant kills one plant species that contains nitrogen-fixing bacteria, but not all plant species that contain nitrogen-fixing bacteria, the ecosystem can still continue to fix nitrogen.
  • Species requiring specialized habitats are prone to declines, however, species may decline in abundance without complete habitat destruction.
  • Humans have been moving animals, plants and pathogens around the world, with invasive, exotic species posing serious threats to biodiversity as predators, pathogens, or superior competitors to native species.
  • Threats to biodiversity include toxic contaminants such as pesticides, heavy metals, acids, and oil spills, as well as endocrine disrupters can have non-lethal effects that prevent or inhibit reproduction. The release of nutrients cause algal blooms and dead zones, and thermal pollution makes water bodies too hot for some species to survive.
    *Human population growth has lead to a decrease in biodiversity
  • If climate changes due to precipitation or temperature, then biodiversity is threatened. If a species niche changes, this is not always possible to adapt to. Overharvesting occurs when one species is removed faster than the population can replace them, in extreme cases this can cause extinction.

Island Biogeography

  • Theory of island biogeography: Habitat size and distance determine species richness.
  • Larger islands support more species meaning the larger the island, the greater the biodiversity:
    • Species richness increases as habitat size increases.
  • Islands closer to the mainland support more species:
    • Easier to colonize areas closer to the mainland
  • Islands are colonized by new species arriving from elsewhere.
  • Many island species evolve to be specialists due to limited resources.
  • Specialists face trouble with invasive species (generalists) that outcompete them.

Ecological Tolerance and Niches

  • Fundamental niche: Abiotic conditions where a species can survive, grow, and reproduce.
  • Realized niche: Abiotic and biotic conditions where a species actually lives.
  • Ecological Tolerance: Range of conditions (temperature, salinity, sunlight) an organism can endure.
  • Applies to individuals and species.
    • Optimal range: range where organisms survive, grow and reproduce
    • Zone of Physiological Stress: range where organisms survive, but experience some stress such as infertility, lack of growth, decreased activity
    • Zone of Intolerance: range where organism will die
  • Every species has optimal environment.

Natural Disruptions to Ecosystems

  • Intermediate disturbance hypothesis: The hypothesis that ecosystems experiencing intermediate levels of disturbance are more diverse than those with high or low disturbance levels.
    • Number of algal species observed in response to different amounts of herbivory by marine snails. When few or many snails are present, there is a low diversity of algal species, but when an intermediate density of snails are consuming algae, the snails cause an intermediate amount of disturbance and a higher diversity of algal species can persist in the ecosystem.
  • Niche generalist A species that can live under a wide range of abiotic or biotic conditions.
  • Niche specialist A species that is specialized to live in a specific habitat or to feed on a small group of species
  • Niche specialists do well when environmental conditions remain relatively constant; however loss of a favored habitat or food source leaves them with few alternatives for survival.
  • Niche generalists fare better under changing conditions because they have a number of alternative habitats and food sources available.

Adaptations and Evolutions

**The death of the last member of a species. Organisms adapt to their environment over time, both short and long term scales through incremental changes at the genetic level.
Environmental changes may be either sudden or gradual, May threaten a species’ survival – individuals will alter behaviors, move or die

  • Microevolution Evolution below the species level.
  • Macroevolution Evolution that gives rise to new species, genera, families, classes, or phyla.

Adaptations

Evolution by artificial selection The process in which humans determine which individuals breed, typically with a preconceived set of traits in mind.

  • Artificial selection has produced numerous breeds of livestock and pets.
  • Most modern agricultural crops are the result of many years of careful breeding.
  • Artificial selection can also produce unintended results such as herbicide resistance.

Evolution by natural selection The process in which the environment determines which individuals survive and reproduce. Key ideas of the theory of evolution:

  • Individuals produce an excess of offspring.
  • Not all offspring can survive.
  • Individuals differ in their traits.
  • Differences in traits can be passed on from parents to offspring.
  • Differences in traits are associated with differences in the ability to survive and reproduce.
    The five random processes through which evolution occurs:
  • Mutation
  • Gene flow
  • Genetic drift
  • Bottleneck effects
  • Founder effects
  • Mutation A random change in the genetic code produced by a mistake in the copying process.
  • When mutations occur in cells responsible for reproduction those mutations can be passed on to the next generation.
  • Sometimes a mutation improves an organism’s chances of survival or reproduction. If such a mutation is passed along to the next generation, it adds new genetic diversity to the population.
  • Gene flow The process by which individuals move from one population to another and thereby alter the genetic composition of both populations.
  • The arrival of individuals from adjacent populations alters the frequency of alleles in the population.
  • In a population that is experiencing natural or artificial selection, high gene flow from outside can prevent the population from responding to selection.
  • Gene flow can be helpful in bringing in genetic variation to a population that lacks it.
  • Genetic drift A change in the genetic composition of a population over time as a result of random mating.
  • Like mutation and gene flow, genetic drift is a nonadaptive, random process.
  • Can have a particularly important role in altering the genetic composition of small populations.
  • Bottleneck effect A reduction in the genetic diversity of a population caused by a reduction in its size.
  • Reduced population numbers means reduced genetic variation.
  • Low genetic variation in a population can cause increased risk of disease and low fertility.
  • The bottleneck effect means species are less able to adapt to future environmental changes.
  • Resulting low diversity can lead to decline and extinction.
    • Founder effect A change in the genetic composition of a population as a result of descending from a small number of colonizing individuals
    • Allopatric speciation – speciation that occurs with geographic isolation
  • When a group of individuals goes to a new area that is physically separated from the larger population
  • If the conditions are different enough evolution will occur and a new species will occur
  • Sympatric speciation – evolution of one species into two species without any geographic isolation
  • Usually occurs due to polyploidy – having three or more sets of chromosomes
  • Humans have altered plant species for larger plants and fruits, found in some snails and salamanders
  • Primary succession Ecological succession occurring on surfaces that are bare rock with no soil.
  • Pioneer species such as algae, lichens and mosses will commonly move into unoccupied habitat
  • Secondary succession
  • The succession of plant life that occurs in areas that have been disturbed but have not lost their soil.
  • Primary succession
    Primary succession occurs in areas with bare rock and no soil. Early- arriving plants and algae can colonize bare rock and begin to form soil, making the site more hospitable for other species to colonize later. Over time, a series of distinct communities develops. In this illustration, representing an area in New England, bare rock is initially colonized by lichens and mosses and later by grasses, shrubs, and trees.
  • Secondary succession
    Secondary succession occurs where soil is present, but all plants have been removed. Early- arriving plants set these areas on a path of secondary succession. Secondary succession in a New England forest begins with grasses and wildflowers, which are later replaced by trees.
  • Lakes are filled with sediments and slowly become terrestrial habitats.