Exam sheet
Speciation
Definition
Allopatric Speciation: This type of speciation occurs when populations of a species become geographically isolated from one another, preventing gene flow. Over time, these populations may evolve independently, leading to the emergence of new species.
Sympatric Speciation: This occurs when populations in the same geographic area diverge into separate species due to reproductive barriers, even without physical separation. This can happen through mechanisms such as polyploidy, habitat differentiation, or sexual selection.
Differences
Geographic Isolation: Allopatric speciation involves a physical barrier, whereas sympatric speciation does not require such barriers.
Mechanisms of Divergence: Allopatric relies on environmental changes or dispersal that separates populations, while sympatric often involves genetic changes like polyploidy or changes in preferences for mating (sexual selection).
Examples
Allopatric: Darwin's finches on the Galapagos Islands, which evolved distinct traits based on their isolated environments.
Sympatric: Cichlid fish in African lakes, which have diversified into multiple species in the same water body, often driven by dietary preferences and mating behaviors.
Reproductive Barriers
Reproductive barriers evolve as populations diverge, which include:
Prezygotic Barriers: Prevent mating or fertilization (e.g., temporal, behavioral isolation).
Postzygotic Barriers: Occur after fertilization (e.g., hybrid sterility, hybrid breakdown).
Polyploidy
Definition: Polyploidy is the condition where an organism has more than two complete sets of chromosomes.
Autopolyploidy: Results from the doubling of chromosome number within a single species, leading to reproductive isolation from the original population.
Allopolyploidy: Involves hybridization between two species followed by chromosome doubling, allowing the hybrid to become fertile and establish a new species.
Habitat Differentiation and Sexual Selection
Habitat Differentiation: Different niches or microhabitats lead to speciation where populations exploit different resources, reducing competition.
Sexual Selection: Preferences for certain traits by potential mates can drive divergence and contribute to the development of reproductive barriers.
Outcomes of Hybrid Zones
Reinforcement: Hybrid offspring are less fit than parent species, leading to stronger reproductive barriers.
Fusion: If hybrids are as fit as or fitter than parent species, they may fuse into a single species.
Stability: Hybrids continue to be produced without significantly affecting the parent species, maintaining a stable hybrid zone.
Punctuated Equilibrium vs. Gradualism
Punctuated Equilibrium: Suggests that species remain relatively stable for long periods (stasis), interrupted by brief periods of rapid change due to environmental factors.
Gradualism: Proposes that species evolve slowly and steadily over time through a gradual accumulation of small changes.
Biodiversity
Levels
Species Richness: The number of different species in a given area.
Species Evenness: The relative abundance of each species in a community.
Subspecies: Populations that are genetically or morphologically distinct within a species.
Importance
Genetic Diversity: Important for population resilience to environmental changes and diseases.
Ecosystem Diversity: Variability among ecosystems contributes to stability and resilience of the biosphere.
Expressing Species Diversity
Scientists often express species diversity using indices that combine both richness and evenness, such as the Shannon index.
Approximately 1.5 to 2 million species have been described, but estimates suggest that 8 to 10 million species may exist, with the most widely accepted count being around 8.7 million.
Incomplete Species Count
The species count is incomplete due to factors such as undiscovered species, taxonomic challenges, and under-explored habitats.
The largest group of organisms is estimated to be insects.
Latitudinal Gradient
Definition: A pattern where biodiversity tends to be higher in tropical regions and decreases toward the poles.
Reasons: This gradient exists due to factors such as climate, habitat availability, and evolutionary history.
Extinction Dynamics
Mass Extinction: A significant, global decrease in biodiversity over a relatively short time.
Background Extinction: The normal rate of species extinction occurring throughout Earth's history.
Extirpation: Local extinction of a species in a specific geographic area.
Greatest Cause of Biodiversity Loss: Habitat destruction, primarily due to human activities.
Habitat Fragmentation
Definition: The process of dividing large habitats into smaller, isolated patches, negatively impacting species survival.
Consequences: It reduces genetic diversity and disrupts ecosystem services.
Habitat Loss: Most prevalent in tropical rainforest regions, whereas polar and desert regions experience the least.
Pollution and Biodiversity
Pollution, such as chemicals and plastics, leads to habitat degradation, endangering species and reducing biodiversity.
Biomagnification: The process where toxic substances accumulate in higher concentrations at higher levels of the food chain.
Invasive Species and Climate Change
Invasive Species: Non-native species that disrupt local ecosystems and outcompete native species, leading to biodiversity loss.
Climate Change Effects: Alters habitats and forces species to migrate, leading to shifts in community structures.
Regions Most Affected: Coral reefs and Arctic regions are particularly vulnerable to climate change, experiencing rapid changes in temperature and habitat conditions.
Average Rise in Global Temperature: Approximately 1.2°C since the late 19th century, resulting in significant environmental changes.
Greenhouse Gases: The three major ones are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O).
Major Source of Greenhouse Gases: Energy production, particularly from burning fossil fuels, is the leading contributor.
Phenotypic Plasticity
Definition: The ability of an organism to change its phenotype in response to environmental conditions.
Organisms with short generation times may adapt more quickly to stressors like climate change due to faster reproduction and evolution cycles.
Importance and Conservation of Biodiversity
Causes and Consequences
Biodiversity loss is driven by human activities, including habitat destruction, climate change, pollution, and overexploitation.
Consequences include loss of ecosystem services, reduced food security, and diminished medicinal resources.
Ecosystem Services
Biodiversity supports ecosystem services such as pollination, nutrient cycling, and water purification, which are essential for human survival.
Food Security and Medicine
Biodiversity enhances food security by providing a variety of crops and livestock that can withstand pests and diseases.
Its importance in medicine is profound, as many medical treatments are derived from natural substances.
Economic Benefits
Biodiversity boosts economies through agriculture, tourism, and ecosystem services.
Biophilia
The innate human affinity for nature and living systems is termed biophilia, highlighting the importance of conserving biodiversity for overall well-being.
Conservation Biology
Defined as the scientific study of nature and of Earth’s biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction.
Umbrella Species
Species whose conservation protects many other species under their care due to their habitat requirements.
Protecting an umbrella species can help maintain the ecosystem’s overall biodiversity.
Protecting Species
Protecting individual species is not enough; habitat preservation, genetic diversity, and ecosystem stability are also crucial for effective conservation efforts.