Darwin and Ecology MG (1)

Darwin and Ecology Overview

• Selections from Chapters 16, 17, 18, 44, 45

Charles Darwin

• 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.

Paradigm Shift in Understanding

• 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 and Fossils

• 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.

The Evolutionary Process

• Darwin concluded that:

  • Earth must be very old for evolution to occur through descent with modification.

  • Fossils indicate species change, not fixity.

Biogeography

• 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).

Natural Selection

• 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.

Theory of Evolution

• Populations change over time through natural selection.

• Common ancestry of living things but each adapted uniquely to lifestyles.

• Theory unifies various biological observations.

Types of Evolutionary Evidence

• 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).

Molecular Evidence

• All life shares biochemical molecules (DNA, ATP).

• Close relationships indicated by shared genetic material and proteins.

Sexual Selection

• A form of natural selection influencing mate choices and reproductive success.

  • Two forms: female choice and male competition.

Evolution and Populations

• Evolution does not occur in individuals but populations.

• Population Genetics:

  • Studies changes in gene frequencies within populations (gene pool).

Peppered Moth Example

• 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.

Hardy-Weinberg Equilibrium

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

Causes of Microevolution

• Deviations from equilibrium conditions cause change:

  • Genetic mutation, gene flow, nonrandom mating, genetic drift, natural selection.

Genetic Drift

• Changes in allele frequencies due to chance events (e.g., natural disasters).

• More pronounced in small populations.

• Types: Bottleneck effect and Founder effect.

Species Definition

• 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 vs. Convergent Evolution

• Divergent Evolution:

  • Different species evolve from a common ancestor (homologous structures).

• Convergent Evolution:

  • Different species develop similar traits independently (analogous structures).

Reproductive Barriers and Isolation Mechanisms

• Prezygotic Barriers:

  • Habitat, temporal, behavioral, mechanical, and gametic isolation.

• Postzygotic Barriers:

  • Include zygote mortality and hybrid sterility.

Ecology Overview

• 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.

Population Growth Factors

• 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.

Regulation of Population Growth

• Density-independent Factors:

  • Abiotic factors like weather, disasters.

• Density-dependent Factors:

  • Biotic factors including competition, predation, and disease.

Extinction

• Complete disappearance of a species or taxonomic group.