Selection Pressure and Adaptation in Ecology

Selection Pressure

• Selection pressures influence an organism's survival in an environment and can be biotic (living factors) or abiotic (nonliving factors).
• Examples include predation pressure, which can lead to adaptations such as speed in prey animals and camouflage in predators.
• A selecting agent is a specific factor prompting selective pressure, such as cheetahs pressuring wildebeest to be faster.

Biotic and Abiotic Factors

• Biotic factors include predation, food availability, competition, and disease.
• Abiotic factors encompass temperature, light intensity, water availability, soil pH, mineral content, and atmospheric gases.

Cane Toads in Australia

• Introduced in 1935 for pest control, cane toads have become invasive, spreading significantly and evolving over 50 generations.
• Long-legged, fast-moving toads at invasion fronts have a selective advantage, facing less competition for resources.
• Cane toads lay 30,000 eggs at a time and possess poison glands that threaten native predators, leading to species decline (e.g., goannas, northern quolls).

Prickly Pear Distribution in Australia

• Introduced from South America, prickly pear became invasive, rendering 40,000 km of farmland unproductive.
• The introduction of the Cactoblastis moth larvae effectively reduced prickly pear populations, showing biotic selection pressure in action.

Adaptations

• An adaptation is a modification that improves survival in specific environments.
• Structural adaptations involve physical changes, such as blubber in whales for insulation or long fingers in fruit bats for wing support.
• Physiological adaptations include internal changes, such as koalas' low metabolic rates for digesting low-nutrition gum leaves and rattlesnakes producing venom.
• Behavioral adaptations are voluntary actions, like bats huddling for warmth or possums being nocturnal to avoid heat.

Charles Darwin and Evolution

• Darwin's theory of evolution describes how traits favoring survival become more common over generations ("survival of the fittest").
• Natural selection is driven by variations in species, leading to increased survival and reproduction of individuals suited to their environments.
• Finch populations in the Galapagos showcased adaptation through varying beak shapes suited for local resources.

Theory of Evolution by Natural Selection

• Variation, overproduction, competition, adaptation, and speciation are key elements in natural selection.
• Microevolution involves small changes in gene frequencies, while macroevolution encompasses larger evolutionary group changes, often traced through fossils.

Divergent and Convergent Evolution

• Divergent evolution occurs when species share a common ancestor but develop different traits due to varying environmental pressures, exemplified by Galapagos finches.
• Convergent evolution arises when unrelated species evolve similar traits due to similar environmental challenges, as seen in sharks and dolphins.

Punctuated Equilibrium vs. Gradualism

• Gradualism proposes a slow, continuous evolution over time with small changes, while punctuated equilibrium suggests rapid changes followed by stability.
• The fossil record supports both theories, showcasing transitional forms and sudden new species appearances.

Evidence for Evolution

• Biochemical, anatomical, embryological, and biogeographic evidence demonstrates evolution.
• Homologous structures indicate common ancestry through evolutionary modifications (e.g., forelimbs of mammals).
• Vestigial structures are remnants of ancestral features that are reduced and no longer serve their original function.

Fossil Dating Techniques

• Fossils are formed through rapid burial to prevent decomposition and can be classified as impressions, preserved remains, or traces.
• Relative dating orders fossils chronologically, while absolute dating estimates their actual ages using radioactivity.

Modern-Day Examples of Evolution

• Cane toad populations exemplify rapid evolution and adaptation post-introduction.
• Antibiotic-resistant bacteria demonstrate modern evolutionary change, with resistant strains surviving treatment and proliferating in populations.### Antibiotic Resistance
• Bacteria can evolve quickly, leading to populations resistant to common antibiotics.
• The rise of antibiotic-resistant bacteria poses a significant challenge in medical treatment.

Cane Toad Introduction to Australia

• Cane toads were introduced to Australia in 1935 and have since proliferated extensively in northeastern Queensland.
• Their spread is facilitated by several adaptive traits and environmental factors.

Traits of Invasive Cane Toads

• Toads at the invasion front typically exhibit straight-line travel and possess longer legs compared to those in established populations.
• Longer legs contribute to greater endurance and enable faster movement to new areas.

Factors Supporting Cane Toad Population Growth

• A lack of natural predators in Australia has contributed to their successful establishment.
• Availability of abundant food resources enhances their breeding success.
• Favourable environmental conditions facilitate their survival and reproduction.

Reproductive Success and Genetic Adaptation

• Cane toads can lay up to 30,000 eggs at a time, significantly increasing population size.
• Genetic changes favor individuals that arrive first to new locations, enhancing their competitive advantage over later arrivals.
• Those who arrive early tend to have access to more resources, leading to higher breeding success due to reduced competition.

Explore the concepts of selection pressure, including biotic and abiotic factors that affect an organism's survival. Understand the role of invasive species like cane toads in Australia and how they adapt to their environments. This quiz will test your knowledge of ecological principles and adaptations.