Chapters 3-5 Biology – Miller • Levine Ecology Chapters 3-5 Biology – Miller • Levine

What is Ecology? The scientific study of: Interactions among organisms Interactions between organisms and their environment Biosphere – portions of the Earth where life exists (land, water, and air)

Levels of Organization Species – group of organisms that can breed and produce fertile offspring Population – a group of individuals of the same species that live in the same area Community – different populations that live in the same area Ecosystem – all the organisms plus the nonliving environment Biome – group of ecosystems with the same climate and similar communities

Levels of Organization

Energy Flow Sunlight is the main energy source for life on Earth. Autotrophs (producers) – organisms that make their own food Photosynthesis – use light energy to make food Chemosynthesis – use chemical energy to make food

Energy Flow Heterotrophs (consumers) – organisms that must feed on other organisms for energy Herbivores – eat only plants Carnivores – eat other animals Omnivores – eat both plants and animals Detrivores – feed on dead matter Decomposers – break down organic matter

Feeding Relationships Energy flows through an ecosystem in one direction (sun → producers → consumers) Food chain – a series of steps in which organisms transfer energy by eating and being eaten

Feeding Relationships Food web – a network of complex feeding interactions Trophic levels – each step in a food chain or food web 1st – producers 2nd – primary consumers 3rd – secondary consumers 4th – tertiary consumers

Ecological Pyramids Energy Pyramid – shows the amount of energy available at each trophic level Only about 10% of the energy is transferred to the next level Biomass Pyramid – shows the amount of living tissue within each trophic level Pyramid of numbers – shows the number of organisms at each trophic level

Ecological Pyramids

Biotic and Abiotic Factors Biotic factors – the living things that influence organisms Abiotic factors – the nonliving things that influence organisms Light Soil Wind Water Temperature

Habitat and Niche Habitat – the area where an organism lives Niche – the role an organism plays in its habitat No two species can share the same niche in the same habitat

Community Interactions Symbiosis – any relationship in which two species live closely together Mutualism – both species benefit (flowers & insects) Commensalism – one species benefits while the other is neither helped nor harmed (orchids in a rainforest) Parasitism – one organism benefits while the other is harmed (fleas on a dog)

Symbiosis

Populations Population density – the number of individuals per unit area Population growth – increase in size of a population Population size can be affected by: Number of births Number of deaths Immigration – organisms moving into an area Emigration – organisms moving out of an area

Exponential Growth Under ideal conditions with unlimited resources, a population will grow exponentially J-shaped curve

Logistic Growth As resources become less available, the growth of a population slows or stops S-shaped curve

Limiting Factors A factor that causes population growth to decrease The population size will usually remain constant Creates the s-shaped curve Two kinds of limiting factors: Density-dependent Density-independent

Density-Dependent Factors A limiting factor that depends on population size Competition – organisms compete for resources Between members of the same species Between members of different species Parasitism and disease

Density-Dependent Factors Predation – when one species feeds on another Predator – the organism that feeds on the prey Prey – the organism being eaten

Density-Independent Factors Affects all populations, regardless of the population size Unusual weather – heavy storms Natural disasters – tornado, volcanic eruption Seasonal cycles – insects die during winter Human activities – clear-cutting forests

Evolution of Populations Directional selection - form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

Evolution of Populations Stabilizing selection - form of natural selection by which the center of the curve remains in its current position; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end

Evolution of Populations Disruptive selection - form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle

Human Population Growth At first the human population grew slowly About 500 years ago it started increasing rapidly Resembles the J-shaped curve US & World Populations

Survivorship Curves

Ecological Succession The series of changes that occurs in a community over time Primary succession – occurs on surfaces where no soil exists (no previous life) Pioneer species – the first species to populate the area Lichens → mosses → grasses → shrubs → trees

Primary Succession

Ecological Succession Secondary Succession – when a disturbance changes the existing community without removing the soil Tornadoes, fire, clear cutting Occurs much quicker than primary succession Climax community – the relatively stable final community Ex. Mt. St. Helens