Introduction to Biodiversity
Unit 2.1: Introduction to Biodiversity
Module 14: The Biodiversity of Earth
Complexity Levels and Biodiversity
Nature operates at various levels of complexity.
Simplest Level: Natural selection operates here.
Species Definition
Species: A group of organisms which is distinct from other groups based on:
Size
Shape
Behavior
Biochemical properties
Capable of interbreeding and producing viable offspring.
Key Note: Different species may mate but will not produce viable offspring.
Measurement of Biodiversity
The number of species in any given location is a primary measure of biodiversity. Estimating the total number of species presents challenges.
Insects are estimated to comprise the largest portion of species, possibly numbering around 10 million!
Diversity Types in an Ecological Context:
Habitat Diversity: The variety of ecosystems within a given region.
Species Diversity: The variety of species in a given ecosystem.
Genetic Diversity: The variety of genes within a given species.
All three types are vital for understanding biodiversity in an area or ecosystem.
Calculating Biodiversity
Species Richness: The total number of species in a specified area.
Species Evenness: The relative proportion of individuals across different species in a given area.
Is one species dominant, or is representation even among various species?
Examples:
Community 1 exhibits higher biodiversity with both richness and evenness assessed.
Shannon-Wiener Index
Description: A formula that combines species richness and evenness into a single calculation.
Variables:
n = Total number of species in the community
pi = Proportion of individuals of species in decimal form
ln = Natural logarithm
A higher number results in higher biodiversity.
Phylogeny and Evolutionary Relations
Phylogeny: illustrates the evolutionary relationships among species,
Biodiversity is essential for species survival. The more genetically diverse a population is (having a larger gene pool), the more effectively it can respond to environmental stressors.
Mechanisms of Evolution
Evolution: Defined as a change in the genetic composition of a population over time.
Evolution can occur in three primary ways:
Natural Selection (as outlined in Darwin’s Theory)
Artificial Selection (Human-driven selection, discussed further in Unit 9)
Random Processes (e.g., bottleneck effects)
Example: Wildfires decimating koala populations, thus erasing genetic diversity.
Darwin’s Theory of Natural Selection
Key components:
Individuals produce an excess of offspring—many cannot survive.
Individuals within a population possess different traits.
These traits can be inherited by offspring.
Variations affect survival and reproductive success.
Adaptations
Adaptation: Any trait that enhances an individual's fitness (i.e., survival and reproductive ability).
Fitness: The relative survival and reproductive success of an individual.
Example: The Peppered Moth, which demonstrates adaptation changes based on environmental conditions.
Random Processes of Evolution
Mutation:
Defined as a random change in the genetic code, resulting from errors in DNA replication.
Most mutations are harmful; however, some can enhance survival. These beneficial mutations can increase genetic diversity if spread to future generations.
Gene Flow:
The transfer of genetic material through movement of individuals between populations, altering genetic composition.
Example: Introduction of panthers from Texas into the Florida panther population.
Genetic Drift:
A non-adaptive random process influencing genetic makeup over time through random mating events.
Consequences: Small populations may experience significant changes in genetic diversity, such as black mice struggling to find mates in their dwindling environments.
Bottleneck Effect:
Reduction in genetic diversity due to a significant decrease in population size caused by factors like habitat loss or natural disasters.
Examples: Piebald deer, white tigers, and the decline of the koala population due to Australian wildfires.
Founder Effect:
Population changes arising from a small group of colonizing individuals. As they establish a population in a new environment, adaptation requirements change.
Example: A rat population in Lancaster might have a higher prevalence of the polydactyl gene due to this effect.
Importance of Biodiversity
Biodiversity is crucial for the survival of species and ecosystems.
A more diverse ecosystem can better recover from disruptions.
Loss of Habitat: Leads to a cascade of species being affected:
Specialist Species: Species well adapted to specific environments are lost first.
Generalist Species: Species that can thrive in diverse environments follow.
E.g., removal of a grasshopper from a food chain results in a collapse of the community as the frog, snake, and hawk are affected.
In a food web, only the frogs may suffer without the grasshopper, thus maintaining some integrity of the community.
Ecological Tolerance
All organisms have a range of tolerance, which represents the conditions they can endure before injury or death occurs.
Example: Coral bleaching, which occurs when higher temperatures cause coral to lose their symbiotic algae, resulting in the coral turning white or bleaching.
Realized Niche: The spectrum of biotic and abiotic conditions in which a species actually lives.
Niche Generalist: Species that thrive in varied environmental conditions.
Niche Specialist: Species that can only survive in narrow conditions, thus making them more vulnerable to extinction.
Module 21: Community Succession
Ecological Succession
Definition: The predictable replacement of one group of species by another group of species over time.
Pioneer Species
Pioneer Species
Definition: A species that can colonize new areas rapidly and grow well in full sunlight.
Types of Succession
Primary Succession
Occurs on surfaces that are initially devoid of soil (e.g., bare rock).
Example: Can be colonized by algae, lichens, and moss which, upon dying, create organic matter.
Disruptions leading to Primary Succession:
Anthropogenic Causes:
Nuclear explosions
Mountain removal
Abandoned parking lots
Natural Causes:
Volcanic eruptions (cooling lava)
Newly exposed rock from retreating glaciers
Secondary Succession
Occurs in areas that have been disturbed but have not lost their soil.
Example: After events like fires or hurricanes.
Disruptions leading to Secondary Succession:
Anthropogenic Causes:
Forest fires
Logging
Mining/Fossil fuel extraction
Natural Causes:
Grasses being replaced by better competitors
Introduction of species with easy seed dispersal (e.g., wind, cherry pits)
Pioneer species such as aspens and cherry trees that rapidly colonize areas and thrive in sunlight; these species can eventually overgrow and shade out others.
Next, shade-tolerant species like beeches grow tall, outcompeting pioneers and eventually dominating the area.
Disturbances can be on a large scale (e.g., entire forests chopped) or small scale (e.g., one tree dying or being uprooted).
Aquatic Succession
Following disturbances like storms, diatoms are the first to colonize, followed by red and green algae, and then barnacles.
Keystone Species
Keystone Species
Definition: A species that plays a role in its community far more important than its relative abundance might suggest.
Types of Keystone Species:
Ecosystem Engineers:
Create or maintain habitats for other species.
Examples:
Bees: Help keep plants alive by pollination.
Beavers: Change the environment through dam-building.
Elephants: Preserve grasslands by eating small trees.
Bears: Maintain populations of moose and elk through seed dispersal from droppings.
Flagship Species
Flagship Species
Definition: The most popular and iconic species used to raise awareness for areas that need protection.
Note: They are not necessarily the most at risk but are used due to their recognizability.
Indicator Species (Bioindicators)
Indicator Species
Definition: A plant or animal that, by its presence, abundance, scarcity, or chemical composition, indicates some distinctive aspect of the health or quality of an ecosystem.
Characteristics of Indicator Species:
Demonstrate environmental health.
Examples:
Birds: Declining numbers indicate habitat destruction.
Trout: Presence indicates water quality.
Lichen: Indicates air quality.
Milkweed: Can indicate ground-level ozone.
Amphibians: Presence of estrogen in water indicates pollution.
Invertebrates: Their diversity indicates water quality.
Species Richness
Species Richness
Definition: The number and types of species present in a community, influenced by various factors.
Influencing Processes:
Colonization of the area by new species.
Speciation within the area.
Losses from the area due to extinction.
Influencing Factors:
Latitude: Species number decreases from the equator towards the poles.
Time: Longer existence of a habitat allows for more colonization, speciation, and extinction.
Habitat Size: Larger habitats typically support more species.
Distance from Other Communities: Closely positioned communities usually have more species.
Note: Factors 3 and 4 are the basis for the theory of island biogeography.