Biology: Trade-offs, Homeostasis, and Metabolism

1. Trade-offs, Homeostasis, and Metabolism 

Trade-offs in Organismal Performance 

● Organisms face trade-offs between: 

○ Fecundity (number and investment in offspring) 

○ Growth (size, defense) 

○ Longevity (lifespan) 

● Example: Eastern Fence Lizards show differences in energy intake (MEI) based on temperature and population origin. 

Temperature and Performance 

● All organisms have a narrow temperature range where performance peaks. ● Acclimation: short-term physiological adjustments. 

● Adaptation: long-term physiological/genetic changes. 

● Evolution: changes in allele frequencies over generations. 

Homeostasis 

● The ability to maintain stable internal conditions. 

● Key concepts: 

○ Ectotherm: heat from environment. 

○ Endotherm: heat from internal metabolism. 

○ Poikilotherm: variable body temperature. 

○ Homeotherm: constant internal temperature. 

○ Stenotherm: narrow thermal tolerance. 

Heat Balance Equation: 

HS = Hm ± Hcd ± Hcv ± Hr - He 

● Metabolism, conduction, convection, radiation, evaporation. 

Mechanisms of Temperature Regulation 

1. Anatomy: 

○ Insulation (fur, feathers, blubber) 

○ Coloration 

○ Counter-current heat exchange (rete mirabile) 

○ Thermal inertia (whales) 

2. Physiology: 

○ Bradycardia (diving reflex) 

○ Vasoconstriction 

○ Sweating / Evaporative cooling 

3. Behavior: 

○ Basking, migration, hibernation 

2. Water Balance and Temperature Trade-offs 

Water Balance in Animals 

● Equation: Water = Wd + Wf + Wa – We – Ws 

○ Ingestion, food metabolism, absorption vs. evaporation and secretion. 

● Adaptations include behavior, physiology, and habitat use.

Water Balance in Plants 

● Transpiration: water loss through stomata. 

● Evapotranspiration: balance between water gain and environmental loss. ● Trade-off: water conservation vs. photosynthesis efficiency. 

● Potential Evapotranspiration (PET): atmospheric demand for water. 3. Metabolism and Energy Use 

Photosynthesis 

● CO₂ + H₂O → CH₂O + O₂ (uses light energy) 

● Reduces carbon; stores energy in chemical bonds. 

Respiration 

● Opposite of photosynthesis. 

● Oxidizes sugars to release stored energy. 

Metabolic Strategies 

● Photosynthetic autotrophs (e.g., plants, cyanobacteria) 

● Chemosynthetic autotrophs (e.g., sulfur bacteria) 

● Heterotrophs (e.g., animals, fungi) 

Photosynthetic Pathways 

● C3: common, less efficient in hot/dry areas. 

● C4: spatial separation of fixation and synthesis (e.g., corn). 

● CAM: temporal separation (e.g., cacti), open stomata at night. 

4. Energy Limitation and Optimal Foraging 

Energy Trade-offs 

● Even abundant resources can’t be fully utilized due to physiological constraints. ● Pmax: max photosynthesis rate. 

● Isat: light level needed to reach Pmax. 

Animal Functional Response 

● Type I: linear increase then plateau (e.g., filter feeders) 

● Type II: decelerating intake (common) 

● Type III: sigmoidal curve; low response at low prey density. 

Optimal Foraging Theory (OFT) 

● Predicts how organisms maximize net energy gain. 

● Trade-offs: foraging time vs. handling time. 

● Applied to both animals and plants (e.g., root/shoot allocation). 5. Life History Strategies 

Life Cycles 

● Asexual vs. Sexual reproduction. 

● Types: Gametic (humans), Zygotic (fungi), Sporic (ferns). 

Key Traits 

● Age at maturity, number/size of offspring, lifespan. 

● Trade-offs: investing in current vs. future reproduction.

r/K Selection 

Plant Life Strategies (Grime’s Model) 

● Ruderals: tolerate disturbance. 

● Stress-tolerators: conserve in poor conditions. 

● Competitors: thrive in resource-rich, stable areas. 

6. Population Ecology 

Population Growth Models 

● Geometric growth: pulsed reproduction. 

● Exponential growth: continuous reproduction. 

● Nt = N₀λᵗ (geometric), dN/dt = rN (exponential) 

● Logistic growth: includes carrying capacity K. 

○ dN/dt = rN(1 - N/K) 

Density Factors 

● Density-dependent: effects intensify as population grows (e.g., disease, competition). ● Density-independent: unrelated to density (e.g., weather). 

7. Distribution and Abundance 

Factors Influencing Distribution 

● Direct environment (light, temp) 

● Indirect effects (predators, symbiosis) 

● Microclimate 

● Biotic interactions (competition) 

Fundamental vs. Realized Niche 

● Fundamental: potential range. 

● Realized: actual due to competition, predation. 

Patterns of Distribution 

● Random, Regular, Clumped 

○ Random: organisms indifferent to other individuals and environment 

○ Regular: organisms antagonistic with other individuals and resources are depleted ○ Clumped: organisms attracted to other individuals or individuals attracted to a common resource

● Small-scale vs. large-scale patterns. 

Abundance 

● Inverse relationship between body size and population density. 8. Dispersal and Metapopulations 

Dispersal Types 

● Range expansion (e.g., invasive species) 

● Within-range movement 

● Metapopulation dispersal: multiple subpopulations connected by migration. Source-Sink Dynamics 

● Source: high-quality habitat, exports individuals. 

● Sink: poor-quality, needs immigration to persist. 

9. Competition 

Types 

● Intraspecific: within same species. 

● Interspecific: between different species. 

Lotka-Volterra Competition Model 

● Adds competition coefficients (α) to logistic growth. 

● Predicts outcomes: coexistence or competitive exclusion. 

Niche Partitioning 

● Species evolve to use different resources to reduce overlap. ● Examples: warblers, barnacles, Anolis lizards. 

10. Consumer-Resource Interactions 

Types of Exploitation 

● Herbivory, Predation, Parasitism, Amensalism 

Predator-Prey Cycles 

● Modeled using Lotka-Volterra: 

○ dNh/dt = rhNh – pNhNp (prey) 

○ dNp/dt = cpNhNp – dpNp (predator) 

Stabilizing Factors 

● Refuges, alternative prey, time lags, predator inefficiency. 

Refuges 

● Space, numbers, morphology, size, behavior. 

11. Community Ecology 

Community Diversity 

● Species richness: number of species. 

● Evenness: relative abundance of each. 

Diversity Indices 

● Shannon-Wiener Index: accounts for richness & evenness. 

● Simpson’s Index: probability two individuals are same species.

Rank-Abundance Curves 

● Visualize abundance and evenness. 

● Flat slope = high evenness, steep = dominance by few species. Environmental Complexity 

● More complex environments → more niches → greater diversity.