EcologyEcology

Chapters 3-5Chapters 3-5

BiologyBiology – Miller – Miller • Levine• Levine

What is Ecology?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 OrganizationLevels 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 OrganizationLevels of Organization

Energy FlowEnergy 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 FlowEnergy 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 RelationshipsFeeding 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 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 PyramidsEcological 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 PyramidsEcological Pyramids

Biotic and Abiotic FactorsBiotic 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 NicheHabitat 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 InteractionsCommunity 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)

SymbiosisSymbiosis

Ecological SuccessionEcological 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 SuccessionPrimary Succession

Ecological SuccessionEcological 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

PopulationsPopulations

• 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 GrowthExponential Growth

• Under ideal conditions with unlimited resources, a population will grow exponentially

• J-shaped curve

Logistic GrowthLogistic Growth

• As resources become less available, the growth of a population slows or stops

• S-shaped curve

Limiting FactorsLimiting 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 FactorsDensity-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 FactorsDensity-Dependent Factors

• Predation – when one species feeds on another– Predator – the organism that feeds on the prey– Prey – the organism being eaten

Density-Independent FactorsDensity-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

Human Population GrowthHuman Population Growth

• At first the human population grew slowly

• About 500 years ago it started increasing rapidly

• Resembles the J-shaped curve US & WorldPopulations