Notes on Evolution and Biodiversity

Evolution and Biodiversity: Comprehensive Notes

• The variety of life on Earth is shaped by natural selection acting on populations within specific environments. With time, populations can adapt to changing environments, but extinction is also a natural part of this process. Today, human activities are changing environments rapidly, causing some species to go extinct or become endangered because they cannot adapt quickly enough.

• Invasive species are non-native species whose introduction causes or is likely to cause economic or environmental harm or harm to human health. Introductions can be accidental (e.g., brown tree snake, zebra mussel) or intentional (e.g., Asian carp for aquatic weed control). Extinction is the complete loss of a species from an area; this can be local (extirpation) or global.

• Key ideas around evolution and natural selection:

  • Key Concept a: Populations adapt to changing environments when individuals with inherited traits that increase survival or reproduction leave more offspring with those traits on average. This process is natural selection.
  • Key Concept b: Individuals do not evolve; populations do. A population is said to have evolved if the gene frequencies in a descendant population differ from those in its ancestral population.

• Genetic variation underpins evolution. Individuals within a population are genetically different. All members of a species share the same basic genes (stretches of DNA that direct protein production and influence traits); variation arises because there can be more than one form of each gene (alleles).

  • Example: Earlobes can be attached or unattached due to two alleles.
  • Environment changes create selective pressures (nonrandom influences) that affect survival and reproduction.
  • Adaptations are genetic traits that increase differential reproductive success: those with advantageous traits leave more offspring.

• Natural selection and its outcomes:

  • Natural selection is the process by which the fittest (best adapted) survive to reproduce, increasing the frequency of advantageous traits over generations.
  • It changes gene frequencies across generations (allele frequencies).
  • Introduced by Charles Darwin and Alfred Wallace; the primary driving force of evolution.
  • Modes of selection: stabilizing, directional, and disruptive, depending on which phenotypes are favored.
  • Mechanism: individuals with certain traits have differential reproductive success, leading to shifts in gene frequencies over time.

• Genetic diversity as the raw material for evolution:

  • Higher genetic diversity increases a population’s capacity to withstand environmental change.
  • Genetic variation arises mainly from mutation (a change in DNA sequence; can be neutral, beneficial, or harmful; generally rare) and genetic recombination (shuffling of alleles during meiosis that creates new allele combinations).
  • Selective pressures from abiotic (e.g., temperature) and biotic (e.g., predators) factors shape which alleles become more common.

• Natural selection in action (classic examples):

  • Rock pocket mouse and rock coloration on lava rocks illustrate how color variants are favored in different habitats.
  • Peppered moth is another classic example of habitat-dependent selection, with genes responsible for coloration not yet identified in some cases.
  • Gene flow can occur between nearby populations, but strong selection can maintain distinct color morphs on different rock backgrounds.

• Coevolution:

  • Key Concept a: Two species can become highly adapted to one another when each becomes the selective pressure shaping traits in the other (coevolution).
  • Key Concept b: Species that never coevolved with a predator or competitor may lack traits needed to survive a new invader.
  • Coevolution is a special case of natural selection where predator and prey, or host and parasite, influence each other’s evolution.

• Random evolutionary events:

  • Alongside natural selection, random events such as genetic drift, bottlenecks, and founder effects influence evolution.

• Genetic drift, bottlenecks, and founder effects:

  • Genetic drift: random changes in allele frequencies that can lead to loss of variants; does not increase adaptation to the environment; strongest in small populations and bottlenecks.
  • Bottleneck effect: drastic reduction in population size leads to loss of genetic variants and reduced diversity.
  • Founder effect: when a small group with subset of genetic diversity becomes isolated, producing a population with different gene frequencies from the original population.

• The pace of evolution and extinction:

  • The pace is generally slow and influenced by population size, genetic diversity, reproductive rate, generation time, and the strength of selective pressures.
  • r-selected species (high reproduction, fast life cycles) tend to evolve faster; many endangered species are K-selected (slower reproduction, higher investment per offspring).
  • Endangered status describes species at very high risk of extinction in the near future.

• Mass extinctions and background extinction rate:

  • Background extinction rate: historically about 1–2 extinctions per 1,000,000 species per year. In math: ext{Background rate}
    oughly rac{1-2}{10^6 ext{ species per year}}.
  • Five major mass extinctions have occurred in Earth’s history, caused by catastrophic environmental changes. Today, human impact appears to be causing another mass extinction.
  • Examples of past mass extinctions:
  • Ordovician extinction: >20% of families lost; ~85% of all marine species extinct.
  • Devonian extinction: >20% of families lost; ~80% of marine species extinct.
  • Permian extinction: 90–95% of all marine species extinct (largest extinction event).
  • Triassic extinction: ~20% of families lost, including many crurotarsans (ancestors of crocodilians).
  • Cretaceous extinction: ~70% of species extinct.
  • Approximately 99% of all species that have ever lived are extinct.

• Case studies and real-world examples:

  • Tree snake hypothesis (Guam): introduction of brown tree snake in the 1940s–1950s caused rapid bird declines; evidence includes geographic correlation, snakes’ predation on birds, and declines in other small mammals. Operation Mouse Drop (2013) attempted to reduce snake populations by releasing acetaminophen-laced mice with radio transmitters to track snakes.
  • Endemism and isolation increase extinction risk because isolated populations have limited genetic diversity and fewer opportunities for recolonization.

• Biodiversity and its measurement:

  • Biodiversity includes genetic, species, and ecological diversity. It provides essential ecosystem services and contributes to human well-being through food, medicine, economy, and recreation.
  • It is estimated that about $1.9 imes 10^{6}$ species have been identified; total species may range from $3 imes 10^{6}$ to $11 imes 10^{6}$ across the Earth.
  • Vertebrates likely comprise roughly 1 ext{%} of all species; insects dominate both known and estimated species counts.
  • Known vs. estimated numbers for major groups (illustrative):
  • Insects: known $1{,}000{,}000$; estimated $5{,}000{,}000$
  • Vertebrates: known $61{,}995$; estimated $80{,}500$
  • Roundworms: known $25{,}000$; estimated $500{,}000$
  • Bacteria: known $7{,}643$; estimated $1{,}000{,}000$
  • Fungi: known $98{,}998$; estimated $1{,}500{,}000$
  • Plants: known $310{,}129$; estimated $390{,}800$
  • Arachnids: known $102{,}248$; estimated $600{,}000$

• Economic and cultural value of biodiversity:

  • Ecosystem services are essential ecological processes that support life and economy. A worldwide study estimated ecosystem services value around $125 imes10^{12}$ dollars.
  • Instrumental value: usefulness to humans; Intrinsic value: right to exist regardless of usefulness.
  • Biodiversity supports cultural, educational, recreational benefits and sustains food, fuel, medicines, and more.

• Types of biodiversity and their roles:

  • Genetic diversity: variation in genes within a population or species.
  • Species diversity: variety of species present (richness) and their relative abundances (evenness).
  • Ecological diversity: variety of habitats, niches, trophic levels, and interactions within ecosystems.

• Endemism and biodiversity hotspots:

  • Endemic species are native to a specific area and not found elsewhere; high endemism often occurs on isolated islands or habitats.
  • Biodiversity hotspots are areas with high endemism and substantial habitat loss (≥70% of original habitat lost). They typically contain >1,500 endemic plant species and about 36 hotspots are recognized, many in the tropics.
  • Sumatra, Borneo, orangutans, pygmy elephants, and other taxa illustrate regional endemism; palm oil expansion threatens hotspots by habitat destruction.

• Isolation and extinction risk:

  • Isolated populations lose gene flow, reducing genetic diversity and adaptive potential; the larger the island and the more niches, the more species it can support, but isolation raises extinction risk.
  • Large islands with more niches may harbor more species, but isolation limits immigration and recolonization.

• Threats to biodiversity (five major categories):

  • Habitat destruction and fragmentation: alteration of natural areas; development, agriculture, mining, dams.
  • Climate change: shifting habitats; specialists are most vulnerable (e.g., polar bears).
  • Pollution: toxic impacts on species and habitats (pesticide impacts, Mekong dolphin decline).
  • Invasive species: outcompete or prey on natives, driving extinctions.
  • Overexploitation: overharvesting and depletion of populations (oyster reefs, etc.).

• Human activities and species protection numbers (illustrative threats data):

  • Overharvesting: 6{,}241 threats counted
  • Agriculture and aquaculture: 5{,}407
  • Urban development: 3{,}014
  • Invasive species: 2{,}298
  • Pollution: 1{,}901
  • Ecosystem modification (dams, etc.): 1{,}865
  • Climate change: 1{,}688
  • Human disturbance (recreation, war): 1{,}223
  • Transportation infrastructure: 1{,}219
  • Energy production: 913

• Conservation approaches: single-species vs ecosystem-based

  • Single-species conservation focuses on high-profile species (flagship species) and aims to increase population numbers; success stories exist (e.g., bald eagle, American alligator), but scope is limited to selected species.
  • Ecosystem-based conservation focuses on protecting habitats and whole ecosystems to safeguard all resident species; includes ecosystem restoration and landscape approaches.
  • Landscape conservation uses a landscape species suite—indicator species chosen to represent ecosystem health and resource needs across habitats; protecting them supports broader ecosystem protection.

• Conservation genetics and ivory trade:

  • Conservation genetics uses genetic data to identify endangered populations and trace illegal trade (e.g., ivory DNA to map poaching hotspots).
  • Five genetically distinct elephant populations identified in Africa via dung samples; DNA microsatellites (short, noncoding repeats) serve as genetic fingerprints to track origin of tusks and poaching activity.
  • DNA microsatellites are nonfunctional; they accumulate changes over generations and help identify population structure.

• Legal protection and international treaties:

  • CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora): regulates global trade; in 1990 banned African elephant ivory trade; debates about trade allowances if forest and savanna elephants are separate species.
  • CBD (Convention on Biological Diversity): promotes sustainable use of ecosystems and biodiversity; enforcement limitations and lack of punitive framework.
  • ESA (Endangered Species Act, 1973, USA): protects biodiversity in the United States; strategies include habitat conservation, captive breeding, relinking populations; success stories include bald eagle and American alligator; challenges include landowner disputes and funding.
  • Lacey Act (1900, USA): prohibits sale/purchase of illegally obtained wildlife and import of nonnative species.
  • Ramsar Convention (1971): framework for conservation and wise use of wetlands across borders.

• Protected areas and conservation planning:

  • Protected areas are geographic spaces recognized, dedicated, and managed for long-term conservation of nature; include national parks, wildlife refuges, wilderness areas, nature preserves, reserves, and game reserves.
  • Global protected areas span terrestrial and marine environments with varying levels of protection.

• Community contributions and market-based conservation:

  • Ecotourism provides low-impact travel that supports conservation and benefits local communities.
  • Debt-for-nature swaps: wealthy nations forgive debt in exchange for conservation commitments; billions have been forgiven, funding conservation in debtor nations.
  • Consumer choices influence biodiversity outcomes (buy sustainable products, support green certifications such as RSPO for palm oil).
  • Nonprofit organizations, land trusts, and conservation easements help protect land and biodiversity.
  • Citizen science opportunities enable public participation in conservation.

• Palm oil case study (case study: environmental loss for economic gain):

  • Palm oil comes from oil palm fruits and is used in about half of packaged foods and household products in the US.
  • Global demand rose markedly post-2007 due to health and consumer trends; ~95% of palm oil in the US comes from Malaysia and Sumatra, contributing to deforestation.
  • Environmental costs include: deforestation of >8 million hectares of rainforest in SE Asia; regional climate change, accelerated warming, flooding and erosion, air and water pollution, displacement of orangutans and other species.
  • Natural tropical forests in Indonesia and Malaysia are among the most biodiverse; Sumatra alone hosts thousands of plant species and many tree species, but palm oil plantations have low biodiversity and reduced ecosystem services.
  • Palm oil plantations have lower biodiversity, lower diversity of birds and insects, and poorer ecosystem services: water production and purification, erosion control, carbon storage capacity, and habitat complexity.
  • Sustainable palm oil initiatives include certification schemes (RSPO) and shifts toward productivity improvements to reduce plantation expansion.
  • Consumers can drive change by seeking certified sustainable palm oil and supporting products that use sustainable sources.

• Additional notes on biodiversity and human health:

  • Biodiversity supports ecosystem services that underpin food security, medicine, and health.
  • Habitat destruction and fragmentation reduce ecosystem services and biodiversity, with downstream effects on human populations.

• Final emphasis:

  • Education and understanding of how populations evolve and how humans influence biodiversity are crucial for making informed decisions that protect ecosystems and human well-being.

• Quick recap of key terms:

  • Allele, mutation, genetic recombination, selective pressure, adaptation, natural selection, evolution, gene flow, genetic drift, bottleneck, founder effect, endemic, hotspot, isolation, extirpation, keystone species, flagship species, ecosystem services, intrinsic vs instrumental value, conservation genetics, CITES, CBD, ESA, Lacey Act, Ramsar, RSPO, ecotourism, debt-for-nature swaps.

• Equations and numeric references (LaTeX):

  • Background extinction rate approximation: ext{Background rate}
    oughly rac{1-2}{10^6 ext{ species per year}}.
  • Global species identified and estimates: $N<em>{ ext{identified}} oughly 1.9 imes 10^{6}, ext{ total estimates } N</em>{ ext{total}} <br /> oughly 3 imes 10^{6} ext{ to } 11 imes 10^{6}.$
  • Vertebrates share of life on Earth: ext{Vertebrates}
    oughly 1 ext{% of all species}.
  • Mass extinction event magnitudes (illustrative):
  • Ordovician: >20 ext{ ext{%}} of families; ~85 ext{%} marine species extinct.
  • Devonian: >20 ext{ ext{%}} of families; ~80 ext{%} marine species extinct.
  • Permian: 90$-$95 ext{%} marine species extinct.
  • Triassic: ~20 ext{%} of families extinct.
  • Cretaceous: ~70 ext{%} of species extinct.
  • Economic value of ecosystem services: $ext{approx. } 125 imes 10^{12} ext{ USD}.$

• Important cases and examples mentioned: Guam tree snake case study, peppered moth, rock pocket mouse, deer mice and owl predation, lion and elephant ecosystem roles (keystone), palm oil case study, and elephant poaching crisis.

• Reading guidance: The material emphasizes understanding how natural selection, genetic variation, and ecological interactions shape biodiversity; the role of human actions in accelerating extinctions; and the range of conservation strategies—from protecting individual species to safeguarding ecosystems and landscapes.