ECOLOGY & EVOLUTION DETAILS

By

Vaibhav Kumar Maurya

PhD

Ecology is the scientific study

• of the interactions between organisms and their environment• Interactions between organisms and their environment

Components of ecology

• Abiotic factors – non-living parts of an organism’s environment– Air currents, temperature,

moisture, light, soil

• Biotic factors – all the living things that inhabit the environment

Principles of Ecology

• Ecology – study of relationships between living and nonliving parts of the world

• Ernst Haeckel (1866) – first to use the word to name the study of how organisms fit into their environment

Levels of Organization

Organism

Population

Community

Ecosystem

Biosphere

Biome

Niche vs. Habitat vs. Ecosystem

• Ecosystem – all the organisms in a given area and the abiotic factors that affect them

• Habitat – place an organism lives out its life• Niche – role and position a species has in its

environment– Includes all biotic and abiotic interactions as an organism

meets its needs for survival– If two species are competing for the same niche, one will

most likely drive the other out and take control of the niche.

• What is your niche?

Niche vs. Habitat vs. EcosystemA great blue heron that lives around the Wye Marsh is part of the Wye river ecosystem. The heron and its mate eat fish, frogs, salamanders, snakes, crayfish, mice, aquatic insects, crickets, grasshoppers, and a variety of other insects in Georgian Bay and the Wye Marsh and build a nest in a tree along side the marsh.

• What is the heron’s habitat?• What is the heron’s niche?• What is the heron’s ecosystem?

Relationships

• All living things form relationships with other living things

• Symbiotic Relationship – a relationship between organisms of two different species that live together in direct contact

Commensalism

• One organism benefits – The other is not affected– Examples

– Spanish moss on a tree– Barnacles on a whale– Burdock seeds on a passing animal

Mutualism• Both organisms benefit

– Acacia tree and ants (Pseudomyrmex sp.) – tree provides food for the ants and the ants protect the tree from animals that would eat the leaves

– Lichens: algae and fungus living together. Algae provides food (photosynthesis) and the fungus provides protection and attaches the lichen to the rock or wood where it lives.

Parasitism• One organism benefits,

the other is harmed– Some live with in the host

• Tapeworms• Heartworms• Bacteria

– Some feel on the external surface of the host• Ticks• Fleas• Mistletoe

– Most do not kill their host (at least not quickly)

Ecosystem Requirements

• #1 - Continuous supply of Energy

• #2 – A flow of energy from one population to another

Obtaining Energy

• Autotrophs - use energy from the sun or energy stored in chemical compounds to produce energy

• Heterotrophs – must consume their energy– Herbivores– Carnivores– Omnivores– Detritivore (AKA decomposers)

Herbivores

• Eat plants (autotrophs)

Carnivores

• Eat other heterotrophs– Predators – kill their own food– Scavengers – eat animals that are already dead

Omnivores

• Eat both autotrophs and heterotrophs (plants and animals)

Decomposers and ScavengersDecomposers – decompose organic matter and

return nutrients to soil, water, and air.

Scavengers consume dead organisms.– Ex. fungus, bacteria

Energy Flows through an Ecosystem in a Complex Network of Feeding relationships called a FOOD

WEB.

Food Chain

Energy Pyramid

• The energy pyramid is made of several trophic levels• A Trophic Level (or feeding level) is a group of

organisms whose feeding source is the same number of steps from the Sun. – Primary Producers (Autotrophs) are the First Trophic

Level. – Primary Consumers (Herbivores) are the Second

Trophic Level. – Secondary and Tertiary Consumers (Carnivores and

Omnivores) are the Third and Fourth Trophic Levels.

– Most Animals feed at more than one Trophic Level.

Trophic Levels

• Energy is Lost or Used as it Flows through the Trophic Levels of an Ecosystem.

• Producers (Plants) absorb Energy from the Sun, but only about ½ of the Energy capture from the Sun becomes part of the Plants Body. The other ½ is used for Living and Growing or Lost as HEAT.

• At each Trophic Level, the Energy stored in an organism is about 1/10 that of the Level Below it. (10%).

Trophic Levels

• Because Energy diminishes at each successive Trophic Level, Few Ecosystems can contain more than 4 or 5 Trophic Levels.

• Organisms at Higher Trophic Levels, Large Carnivores, tend to be Fewer in number than those at Lower Trophic Levels, Producers.

Number and Biomass Pyramids

• The number of organisms at each trophic levels decreases as you step up the pyramid.

• Biomass (living organic matter) is reduced at each trophic level as well

Ecology and evolutionary biology are closely related sciences

•Events that occur in the framework of ecological time (minutes, days, years) translate into effects over evolutionary time (decades, millennia). •Example: Hawks feeding on mice impact mouse population and may eventually lead to selection for mice with fur as camouflage.

• Ecological research scale ranges from individuals to the biosphere

What determines distribution & abundance of species?Two classes of answers

1. Contemporary, local factors (domain of traditional Ecology)

2. Historical factors (= evolutionary ones)

•Why different species live in different environments? (Adaptation)

•E.g., long necked giraffe in savannas of Africa (widely dispersed, umbrella-shaped trees); white coated polar bear in Arctic (invisible to prey)

Nature selection as a force of evolutionWhat is Darwin’s natural selection?

The differential success (survival and reproduction) of individuals within the population that results from their interaction with their environment.

“Survival of fitness, elimination of ‘inferior’ individual”

Two conditions (assumptions):• 1. There is variation in populations. Variation is heritable. • 2. In every generation some organisms are more successful at

surviving and reproducing than others. Survival and reproduction are not random, but are related to variation among individuals. Organisms with best characteristics are ‘naturally selected.’

If 2 conditions are met then the population will change from one generation to the next. Evolution will occur.

Evidence of natural selection

• Evolution of beak shape in Finches.• Peter and Rosemary Grant’s (and colleagues) work

on Medium Ground Finches Geospiza fortis.• Darwin’s Finches

Genetic studies show all arise from a single ancestral species.

Heritability is an essential feature of NSHeritability: individual’s characteristics are passed from one generation to the next. Measured

as proportion of the variation in a trait in a population that is due to variation in genes.• Mendel’s genetics and inheritance

Genetic variation is the ingredient for Natural SelectionSources of genetic variation

– Mutation: inheritable changes in a gene or a chromosome

• Gene mutation: (point mutation)

• Chromosome mutation

– deletion, duplication, inversion, translocation

– Genetic recombination

Sexual reproduction

two individuals produce haploid gametes (egg or sperm) – that combine to form a diploid cell or zygote.

– Reassortment of genes provided by two parents in the offspring– Increases dramatically the variation within a population by creating new

combinations of existing genes.

Asexual reproduction: less variation (only mutation)

Evolution is a change in gene frequency• Evolution is a change of gene frequencies within a population (or species)

over time

– Individuals do not evolve, populations evolve

– Focus on gene pool, collective

But why do we see populations are still the ‘same’ over many generations?

• The Hardy-Weinberg Principle:

Gene frequencies will remain the same in successive generations of a sexually reproducing population if the following five conditions hold:

– Random mating

– There is no mutation

– The population is very large

– There is no selection

– There is no migrations (isolated from other populations)

Five Causes of evolution• Mutations

• Gene flow - Emigration and immigration of individuals (Flow of alleles)

• Genetic Drift – Changes in the gene pool of a small population due to chance

• Nonrandom mating: (AA mates AA, Aa)

• Natural selection

Speciation and mechanisms• Speciation: splitting of one species into 2 different species. • Concept of species:

– Biological Species: a species is a group of organisms whose individual have the potential to interbreed and produce fertile offspring.

• Reproductively isolated: don’t produce fertile hybrids• Natural conditions: artificial breeding doesn’t count. For example,

artificial insemination, keeping 2 species locked up together.– Morphological species: members of the same species look similar

to each other. Many examples of organisms that look similar but can’t produce fertile offspring.

– No one species concept applies to all organisms

Mechanism of Speciation– Allopatric speciation (probably most vertebrates)

• allopatric species occupy areas separated by time or space.– Sympatric speciation (especially plants and insects)

• Sympatric species occupy the same place at the same time

• The traits selected for by natural selection need to be inheritable so that the next generation after selection retains the change

• Three types of selection– Directional

• See finches– Stabilizing

• Long necks in giraffes– Disruptive

• Sexual dimorphism

Summary

• What is ecology?

• What are the components of ecology?

• What is niche?

• What are the relationships in ecosystem?

• What is natural selection?

• Different types of NS

• Gene and genetic variation

• Evolution

• Concept of species.

• Speciation and mechanisms