2.1: Introduction to Biodiversity

• Biodiversity: The variability among species, between species, and of ecosystems.

• It can be described and defined at the genetic, species, and ecosystem levels.

  • Genetic diversity: It describes the range of all genetic traits, both expressed and recessive, that make up the gene pool for a particular species.

  • Species diversity: It is the number of different species that inhabit a specific area.

  • Ecosystem diversity: It describes the range of habitats that can be found in a specific area.

• Ecosystems that have high biodiversity are characterized by the following:

  • Abundant natural resources

  • Large genetic diversity

  • Complex food webs involving a variety of ecological niches

  • Large numbers of organisms of different species

  • Large numbers of different species

• Biodiversity is important because it helps keep the environment in a natural balance.

Anthropogenic Activities That Can Reduce Biodiversity

Population Bottleneck

• Population Bottleneck: It is a large reduction in the size of a single population due to a catastrophic environmental event.

  • As a result of the smaller population, there is less genetic diversity in the gene pool for future generations.

• Minimum Viable Population Size: The number of individuals remaining after the bottleneck and how that compares to the smallest possible size at which a population can exist without facing extinction from a natural disaster.

Loss of Habitat = Loss of Specialist Species

• Generalist Species: Species that live in different types of environments and have varied diets.

  • Ex.: Raccoons: They are classified as omnivores as they are able to survive on a large variety of food types.

• Specialist Species: These species require unique resources and often have a very limited diet; they often need a specific habitat in which to survive.

  • Ex.: Giant Panda Bear: They survives almost entirely on bamboo and lives in remote bamboo forests in China.

Species Richness

• Species Richness: The number of different species (diversity) represented in an ecological community or region.

  • If individuals are drawn from different environmental conditions or different habitats, the species richness can be expected to be higher than if all individuals are drawn from similar environments.

2.2: Ecosystem Services

• Cultural Benefits

  • Sustainable fisheries and aquaculture can directly support recreational services.

  • Recreational fishing is linked to healthy aquatic ecosystems.

• Provisioning Benefits

  • Ecosystems provide diversity of materials and products

  • Livestock provide different types of raw material such as fiber (wool), meat, milk

• Regulating Benefits

  • Keep pest populations in balance through natural predators.

  • Keeps food prices lower

  • Reduces the need for pesticides

  • Achieved in ecosystems through the actions of predators and parasites as well as by the defense mechanisms of their prey.

• Supporting Benefits

  • Form new soil and renew soil fertility

  • Allows for greater crop yields, which can feed more people.

  • Reduces the need for fertilizers.

2.3: Island Biogeography

• Island: A suitable habitat for a specific ecosystem that is surrounded by a large area of unsuitable habitat.

• Island Biogeography: It examines the factors that affect the richness and diversity of species living in these isolated natural communities.

• Theory of Island Biogeography: It proposes that the number of species found on an “island” is determined by immigration and extinction of isolated populations.

• Island Biogeography is influenced by the following:

  • Degree of Isolation: Distance to the nearest island or mainland.

  • Habitat fragmentation: It occurs when a habitat is broken into pieces by development, industry, logging, roads, etc., and can cause an edge effect.

  • Habitat suitability

    • Climate

    • Initial plant and animal composition

    • The current species composition.

  • Human activity and subsequent level of disruption

  • Location relative to ocean currents

• Important Points:

  • Closer islands are also easier to find for migrating species.

  • Habitat fragmentation is currently the main threat to terrestrial biodiversity.

  • Islands closer to the mainland have more biodiversity.

  • Island biogeography is used to predict biodiversity and extinction rates in habitat fragmentation on the continents.

  • Larger islands are bigger targets, so migrating species can find them more easily.

  • Larger islands have more biodiversity.

  • Larger islands have higher populations of species and therefore lower extinction rates.

2.4: Ecological Tolerance

• Earth’s ecosystems are affected by both biotic and abiotic factors, and are regulated by the Law of Tolerance.

• Law of Tolerance: It states that the existence, abundance, and distribution of species depend on the tolerance level of each species to both physical and chemical factors within its environment.

• Each organism's success depends on a complex set of conditions, including minimum, maximum, and optimum environmental factors.

• Biological, climatic, and topographic factors affect an organism's abundance and distribution. If these exceed the organism's tolerance, species numbers will decline.

2.5: Natural Disruptions to Ecosystems

• Ecosystem: A community of organisms that interact with each other and their environment and that can change over time.

• Natural and sudden disruptions dramatically affect which species will thrive in an environment and which species will not and will possibly become extinct.

Flooding

• Kills wildlife and their food source

• Soil is no longer held in place by roots.

• Flooding can result in water-saturated soils.

  • Plant roots need oxygen, so saturated soils drown them.

• Flooding may also cause water and nutrients to run off across land surfaces.

  • Burrows, dens, and nests can be destroyed by rushing water, forcing animals to move.

• Floodplain species have adapted to occasional flooding.

  • The flooding deposits nutrient-rich sediment along stream banks.

Volcanic Eruptions

• Kills wildlife and their food source.

• Soil is no longer held in place by roots.

• Volcanic materials break down and weather to form some of Earth's richest soils, which have fed civilizations.

• Over 4.5 billion years, volcanoes and cooling magma condensed steam to create all of Earth's water.

• Volcanoes also contributed to a large portion of Earth’s early atmosphere.

• Sulfur gas and water in the atmosphere form microscopic droplets that stay in the atmosphere for years, cooling the troposphere by 2–3 degrees.

Wildfires

• Kills wildlife and their food source

• Soil is no longer held in place by roots.

• Helps the ecosystem by clearing out dead and dying vegetation to give surviving plants more light.

• Ash and charcoal left from burnt vegetation can help add nutrients to depleted soil. These nutrients provide a rich environment for surviving vegetation and sprouting seeds.

• Several plants actually require fire in their life cycles.

Earth system processes operate on a range of scales

• Episodic Process: Occurring occasionally and at irregular intervals. — El Niño and La Niña

• Periodic Process: Occurring at repeated intervals. — Tide

• Random Process: Lacking a regular pattern. — Meteorite impacts

Sea Levels

• Global sea level has changed significantly over Earth’s history, with sea level being affected by the amount and volume of available water and the shape and volume of the ocean basins.

• The temperature of ocean water, the amount of water retained in aquifers, glaciers, lakes, polar ice caps, rivers, and sea ice, the changing shape of ocean basins, tectonic uplift, and land subsidence all affect sea level.

• The primary reason for changes in sea level today is glaciers and sea ice melts caused by global warming.

• ~30% of sea-level change is due to the melting of glaciers and ice sheets on land.

• ~30% of sea-level change is due to thermal expansion—as the oceans warm (climate change), water expands.

• ~40% of sea-level change is due to coastal land subsidence (sinking).

Wildlife Migrations

• Escaping harsh weather like seeking warmer water for breeding and raising young but returning to colder water for feeding as there is more food available.

• Escaping natural disasters and their environmental aftermaths like wildfires, floods, and storm events.

• Finding natural resources for food.

2.6: Adaptations

• Adaptation: The biological mechanism by which organisms adjust to new environments or to changes in their current environment.

  • Behavioral Adaptation: Such as instincts, mating behavior, or vocalizations.

  • Physiological Adaptation: Such as methods of temperature control or how food is digested

  • Structural Adaptation: Involves physical features such as body coverings.

• Short Term Adaptations

  • Develops in response to temporary changes in the environment;

  • Involves temporary changes;

  • It is not inherited, nor does DNA change; and

  • Plays no role in evolutionary processes.

• Long-term adaptations may involve DNA changing over long time periods in response to natural selection involving evolutionary processes.

2.7: Ecological Succession

• Ecological succession: The gradual and orderly process of ecosystem development brought about by changes in community composition and the production of a climax community and describes the changes in an ecosystem through time and disturbance.

• Facilitation: When one species modifies an environment to the extent that it meets the needs of another species.

• Inhibition: When one species modifies the environment to an extent that is not suitable for another species.

• Tolerance: When species are not affected by the presence of other species.

• Pioneer Species: Earlier successional plants, generalists.

  • Pioneer Plants have short reproductive times.

  • Pioneer Animas have low biomass and fast reproductive rates.

Characteristics of Succession within Plant Communities

Primary vs. Secondary Succession

• Ecological succession: The process of change in the species structure of an ecological community over time, which can be millions of years in the case of primary succession or decades in the case of secondary succession.

• Primary succession: The evolution of a biological community’s ecological structure in which plants and animals first colonize a barren, lifeless habitat.

• Secondary succession: A type of ecological succession in which plants and animals recolonize a habitat after a major disturbance.

Ecological Succession in a Disturbed Ecosystem

• Ecological disturbance: An event or force that can result in mortality to organisms and changes in the spatial patterns in their ecosystem and plays a significant role in shaping the structure of individual populations within the ecosystem.

• The impact that a disturbance has on an ecosystem depends upon:

  • Intensity and frequency

  • Season

  • Size and spatial pattern

  • Topography

• Succession: A directional, non-seasonal, cumulative change in the types of plant species that occupy a given area over time, involving colonization, establishment, and extinction, shows how an ecosystem changes after an ecological disturbance.

• Species Richness generally increases as succession proceeds and generally peaks when it reaches the climax community, but the diversity growth rate gradually slows down as succession advances to the climax community.

  • Species richness: The number of different species represented in an ecological community.

• In the early stages of succession, gross productivity is low due to the initial environmental conditions and low numbers of producers.

• In later stages of succession near the climax community, gross productivity (GP) may be high, but increased respiration (R) balances it, so net productivity approaches zero and the gross production respiration (GP:R) ratio approaches 1:1.

• Changes that occur during succession include the following:

  • Biodiversity increases and then falls as the climax community is reached.

  • The biomass production respiration ratio falls.

  • Early stages of succession have few species.

  • Energy flow becomes more complex.

  • NPP and GPP rise and then fall.

  • Soil depth, humus, water-holding capacity, mineral content and cycling increase.

  • Species-diversity increase continues until a balance is reached between:

    • existing species to expand their range;

    • possibilities for new species to establish; and

    • local extinction.

  • Species diversity increases with succession.

  • The size of organisms increases.

Keystone Species

• Keystone species: A species whose very presence contributes to a diversity of life and whose extinction would lead to the extinction of other forms of life.

• Examples:

  • Certain bat species pollinate critical trees in the rainforest and help disperse their seeds.

  • Grizzly bears transfer nutrients from oceanic to forest ecosystems.

  • Prairie dog burrowing aerates the soil and improves soil structure, while other animals use prairie dog burrows for shelter and hibernation.

  • Sea stars prey on sea urchins, mussels, and other shellfish that have no other natural predators, keeping their populations in check.

Indicator Species

• Indicator species: These are organisms whose presence, absence, or abundance reflects a specific environmental condition and can indicate the health of an ecosystem.

• Examples:

  • Caddisflies, mayflies, and stoneflies require high levels of dissolved oxygen in the water

  • Lichens —some species indicate air pollution

  • Mollusks indicate water pollution

  • Mossesindicate acidic soil

  • Sludge worms indicate stagnant, oxygen-poor water

Chapter 3: Populations