Biodiversity Study Guide

📖 Core Concepts Biodiversity – the total variety of life (genes, species, ecosystems) on Earth. Levels of biodiversity – genetic (DNA variation within a species), species (number & relative abundance of species), ecosystem (variety of habitats & ecological processes), phylogenetic (evolutionary relationships). Functional diversity – range of traits (e.g., feeding mode, mobility) that influence ecosystem functioning. Species richness – count of different species in an area. Species evenness – how equally individuals are distributed among those species. Species diversity – combines richness & evenness (e.g., Shannon, Simpson indices). Latitudinal gradient – species richness rises toward the equator; driven mainly by higher mean temperatures. Biodiversity hotspots – regions with very high endemism that have lost >70 % of original habitat. Mass‑extinction events – six major, rapid loss episodes; the Permian‑Triassic (251 Ma) was the worst. Current drivers – habitat loss (especially agriculture), climate change, overexploitation, invasive species, pollution, human population growth. Ecosystem services – benefits humans obtain (regulating, cultural, economic). --- 📌 Must Remember 8.7 M terrestrial + 2.2 M marine species estimated total. 30 % of all species could be extinct by 2050; ≈140 000 species lost each year. 58 % of global biodiversity lost since 1970 (IPBES). Latitudinal gradient: richness ↑ from poles → equator. Shannon index: \(H' = -\sum{i=1}^{S} pi \ln pi\). Simpson index: \(D = \sum{i=1}^{S} pi^2\) (probability two random individuals are the same species). 30 % by 2030 (“30×30”) protection target; currently 17 % terrestrial, 10 % marine protected. Hotspot definition – high endemism + >70 % habitat loss. Primary human driver – land‑use change for agriculture. Economic value – ecosystem services ≈ $33 trillion/yr (Costanza 1997); biodiversity’s total economic contribution ≈ $150 trillion/yr. --- 🔄 Key Processes Measuring Species Diversity Survey area → count individuals per species → calculate \(pi = \frac{ni}{N}\). Plug \(pi\) into Shannon or Simpson formulas. Post‑mass‑extinction recovery Surviving lineages diversify → speciation outpaces extinction → overall biodiversity rises (exponential trend for vertebrates). Ecological intensification in agriculture Increase in‑field functional diversity (cover crops, pollinators, natural enemies) → enhanced pest control & yield stability. Protected‑area design Identify biodiversity hotspots → prioritize large, connected reserves → add buffer zones to reduce edge effects. Bioprospecting workflow Sample organism → isolate compound → test bioactivity → assess sustainability & benefit‑sharing (Nagoya Protocol). --- 🔍 Key Comparisons Genetic vs. Species Diversity – genetic: variation within one species; species: number of different species present. Planned vs. Associated Diversity (agriculture) – planned: crops, cover crops, introduced beneficial organisms; associated: weeds, pests, pathogens that appear unintentionally. Shannon vs. Simpson Index – Shannon emphasizes rare species (more sensitive to richness); Simpson emphasizes dominant species (more sensitive to evenness). Hotspot vs. Non‑hotspot regions – hotspots: high endemism + high habitat loss; non‑hotspots: lower endemism, often more intact habitats. --- ⚠️ Common Misunderstandings “More species = more ecosystem services” – not always linear; functional trait diversity often drives service provision. “Protected areas automatically stop loss” – effectiveness depends on size, connectivity, enforcement, and surrounding land use. “Invasive species always increase local diversity” – they may raise alpha diversity temporarily but lower gamma (regional) diversity via homogenization. “All biodiversity loss is recent” – Earth has experienced five past mass extinctions; current rates are unprecedentedly fast. --- 🧠 Mental Models / Intuition “Tree of Life” analogy – visualize biodiversity as branches: genetic variation are leaves, species are branches, ecosystems are whole trees, phylogenetic diversity is the total branch length. “Bank account” model for ecosystem services – think of nature’s services as a bank balance: over‑withdrawal (habitat loss) leads to depletion and future deficits (reduced resilience). “Ripple effect” – losing one species can trigger co‑extinctions (e.g., pollinator loss → plant decline). --- 🚩 Exceptions & Edge Cases Invasive species may raise local (alpha) diversity while reducing regional (gamma) diversity. Marine vs. terrestrial richness – terrestrial biodiversity up to 25× marine, but marine species often have larger ranges (higher beta diversity). Phylogenetic diversity can be high even when species richness is low (e.g., isolated islands with ancient lineages). --- 📍 When to Use Which Choose Shannon index when you need a metric that rewards rare species and want a single number for comparative studies. Choose Simpson index for quick assessment of dominance or when sample sizes are uneven. Apply “30×30” target for policy planning; use hotspot maps to allocate limited funds. Select planned diversity interventions (cover crops, pollinator strips) in low‑intensity farms; rely on associated diversity management (weed control) in high‑intensity monocultures. --- 👀 Patterns to Recognize Latitudinal pattern – tropical regions → higher species counts; expect higher threat levels in these areas. Mass‑extinction signature – abrupt drop in fossil diversity followed by rapid rebound in certain clades (e.g., marine invertebrates). Driver clustering – habitat loss + climate change often co‑occur in regions of rapid agricultural expansion. Service‑loss linkage – decline in plant diversity ↔ reduced carbon sequestration, nutrient cycling, and pest regulation. --- 🗂️ Exam Traps “Biodiversity loss is greatest in temperate zones” – distractor; the latitudinal gradient shows highest loss in tropical hotspots. Confusing “species richness” with “species evenness.” Remember richness = count; evenness = distribution. Assuming “all invasive species are harmful.” Some invasives may temporarily raise local diversity; the exam may ask for nuance. Mixing up “genetic diversity” with “phylogenetic diversity.” Genetic = within‑species DNA variation; phylogenetic = evolutionary distance among species. Over‑valuing a single ecosystem service (e.g., pollination) as the only benefit of diversity. Exams often test awareness of multiple regulating, cultural, and economic services. ---