Darwin and Ecology MG (1)

Darwin and Ecology Overview

Born in 1809 and became a naturalist on the HMS Beagle at age 22 (1831)
Undertook a five-year voyage through the Southern Hemisphere
Main mission: Expand knowledge of natural resources in foreign lands
His observations led to the conclusion that biological evolution occurs,
- Inheritable changes over time improve a population's adaptation to its environment.

Pre-Darwin Beliefs:
- Earth was believed to be only a few thousand years old.
- Species considered fixed and unchanging since creation.
Influential Discoveries:
- Fossils brought back by explorers challenged previous notions.
- Fossils found in strata reveal the age of organisms and the historical environment.
- Oldest fossils typically found in the lowest strata.

Geology:
- Study of the Earth's physical structure, history, and processes.
Darwin observed significant geological changes, including:
- Volcanic islands and coral reefs.
- Uplift and subsidence of land, fossil records, and marine fossils in the Andes.
Findings led to:
- Understanding of geological time scales.
- Increasing awareness of extinct species.

Darwin concluded that:
- Earth must be very old for evolution to occur through descent with modification.
- Fossils indicate species change, not fixity.

Study of the distribution of life-forms:
- Observed and compared animals from different regions (e.g., South America and England).
- Convergent Evolution:
  - Example: Patagonian hare resembles European rabbit due to similar environmental adaptations.
- Galápagos Islands Observations:
  - Finches exhibited variations based on food sources, indicating divergent evolution.
  - Tortoises showed adaptations based on habitat (long and short neck variations).

Proposed mechanism for evolution;
- Organisms best suited to their environment tend to reproduce successfully.
- Adaptations:
  - Heritable traits that enhance survival and reproduction (e.g., fitness).
- Most fit individuals capitalize on resources leading to more viable offspring.

Fossil evidence: succession of life forms, transitional fossils like Archaeopteryx.
Biogeographical evidence: distribution patterns influenced by isolation (e.g., marsupials in Australia).
Anatomical evidence: structural similarities due to common descent (e.g., vestigial structures, homologous and analogous structures).

A form of natural selection influencing mate choices and reproductive success.
- Two forms: female choice and male competition.

Evolution does not occur in individuals but populations.
Population Genetics:
- Studies changes in gene frequencies within populations (gene pool).

Dominant allele (D) leads to dark coloration and higher survival in certain environments.
Light-colored moths are more fit in lighter habitats due to better camouflage.

Conditions for stable allele frequencies in populations include no genetic drift, migration, or selection.

Deviations from equilibrium conditions cause change:
- Genetic mutation, gene flow, nonrandom mating, genetic drift, natural selection.

A species is a group of individuals that interbreed to produce viable offspring.
Gene flow occurs within a species, but not between different species.

Divergent Evolution:
- Different species evolve from a common ancestor (homologous structures).
Convergent Evolution:
- Different species develop similar traits independently (analogous structures).

Prezygotic Barriers:
- Habitat, temporal, behavioral, mechanical, and gametic isolation.
Postzygotic Barriers:
- Include zygote mortality and hybrid sterility.

The scientific study of interactions between organisms and their environment.
Population Distribution and Density:
- Influenced by resource availability (light, water, space).
- Patterns: clumped, random, and uniform.

Growth influenced by birth and death rates.
Survivorship Curves: Identifies different survival patterns (Type I, II, III).
Logistic vs Exponential Growth:
- Exponential: Rapid growth under optimal conditions.
- Logistic: Growth slows as resources become limited, stabilizing at carrying capacity.

Density-independent Factors:
- Abiotic factors like weather, disasters.
Density-dependent Factors:
- Biotic factors including competition, predation, and disease.