Ecology Study Guide

Characteristics of Life

Defining Life

Biologists define life by identifying a set of characteristics shared by all living organisms. These features distinguish living things from non-living matter and help organize biological study.

• Order: Living things are highly organized, composed of one or more cells. Cells are the basic units of life.

• Reproduction: Organisms can produce new individuals of the same type, ensuring the continuation of their species.

• Growth and Development: Organisms grow and change over time, following specific instructions encoded in their DNA.

• Energy Processing / Metabolism: Living things obtain and use energy, carrying out chemical reactions to sustain life. Example Equations: Photosynthesis: $6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$ Cellular Respiration: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}$

• Regulation / Homeostasis: Organisms maintain stable internal conditions (homeostasis) distinct from their external environment.

• Response to Stimuli / Environment: Living things sense and respond to changes in their surroundings.

• Evolutionary Adaptation: Populations of organisms change over generations, adapting to their environment through natural selection.

Example: A rose bush grows and develops, responds to sunlight, reproduces by forming seeds, and maintains water balance through its cells.

Cellular Organization

Prokaryotic vs. Eukaryotic Cells

All living organisms are made of cells, which can be classified as prokaryotic or eukaryotic.

• Prokaryotic Cells: - No membrane-bound nucleus - DNA is located in the cytoplasm - Few organelles - Examples: Bacteria, Archaea

• Eukaryotic Cells: - Membrane-bound nucleus - DNA is enclosed within the nucleus - Many organelles (e.g., mitochondria, chloroplasts) - Examples: Plants, Animals, Fungi, Protists

Comparison Table:

Feature	Prokaryotic Cell	Eukaryotic Cell
Nucleus	Absent	Present (membrane-enclosed)
Organelles	Few	Many
DNA Location	Cytoplasm	Nucleus
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists

Unit: Ecology

Introduction to Ecology

Ecology is the scientific study of the interactions between organisms and their environment, including both biotic (living) and abiotic (non-living) factors.

• Biotic Factors: Living components such as plants, animals, bacteria, fungi.

• Abiotic Factors: Non-living components such as sunlight, temperature, water, soil, and nutrients.

Example: In a savanna, giraffes (biotic) interact with trees (biotic) and water availability (abiotic).

Levels of Ecological Organization

• Individual: Single organism

• Population: Group of individuals of the same species in an area

• Community: Populations of different species living and interacting together

• Ecosystem: Community plus abiotic environment

• Biosphere: All ecosystems on Earth

Population Ecology

Population Concepts

• Population: Group of individuals of a single species living in the same general area.

• Density: Number of individuals per unit area.

• Dispersal: Pattern of spacing among individuals.

Patterns of Dispersal

• Random: Unpredictable spacing, rare in nature.

• Uniform: Even spacing, often due to antagonistic interactions.

• Clumped: Most common; individuals aggregate near required resources.

Survivorship Curves

Survivorship curves show the proportion of offspring that survive to different ages.

• Type I: High survival early and middle life, rapid decline in older age (e.g., humans, elephants).

• Type II: Constant death rate throughout life (e.g., some birds, reptiles).

• Type III: High death rate early in life, survivors live long (e.g., trees, fish).

K-selected vs. r-selected Species

Feature	K-selected Species	r-selected Species
Size	Large	Small
Reproduction	Few, large offspring; much parental care	Many, small offspring; little parental care
Sexual Maturity	Later	Early
Competition	High	Low

Population Growth Models

• Exponential Growth: Population increases rapidly under ideal conditions. Equation: $\frac{dN}{dT} = r_{max}N$

• Logistic Growth: Population growth slows as it approaches carrying capacity (K). Equation: $\frac{dN}{dT} = r_{max}N \left(\frac{K-N}{K}\right)$

Definitions: $N$ = population size $r_{max}$ = maximum per capita rate of increase $K$ = carrying capacity

Factors Affecting Population Growth

• Density-Dependent Factors: Effects increase with population density (e.g., predation, disease, competition).

• Density-Independent Factors: Effects are unrelated to population density (e.g., natural disasters).

Community Ecology

Community Interactions

• Competition (-,-): Both species are harmed by competing for the same resource.

• Competitive Exclusion Principle: Two species competing for the same resource cannot coexist indefinitely; the better competitor will exclude the other.

• Resource Partitioning: Species with overlapping niches may coexist by using resources differently.

• Fundamental Niche: The full range of environmental conditions a species can occupy.

• Realized Niche: The actual conditions a species occupies due to competition.

Condition	Realized Niche	Fundamental Niche
Size	Small	Large
Competition	Yes	No
Limiting Factors	Many	Few
Nature of Niche	Actual	Ideal/Theoretical
Synonyms	Post-competitive	Pre-competitive

Other Community Interactions

• Exploitation (+,-): One species benefits, the other is harmed (e.g., predation, herbivory, parasitism).

• Mutualism (+,+): Both species benefit (e.g., pollination).

• Commensalism (+,0): One species benefits, the other is unaffected.

Keystone Species

A keystone species has a disproportionately large effect on its community. Its removal can cause significant changes in ecosystem structure.

Ecological Succession

• Primary Succession: Occurs in lifeless areas where soil has not yet formed (e.g., after a glacier retreats).

• Secondary Succession: Occurs in areas where a disturbance has destroyed a community but left the soil intact (e.g., after a fire).

Energy and Matter in Ecosystems

Energy Flow

• Energy enters ecosystems as sunlight and is converted by producers (plants) into chemical energy.

• Energy flows through trophic levels: producers → consumers → decomposers.

• Energy transfer is inefficient; only about 10% of energy is passed to the next trophic level.

Matter Cycling

• Matter (e.g., carbon, nitrogen) cycles between biotic and abiotic components of ecosystems.

• Decomposers play a key role in recycling nutrients.

Additional info: These notes expand on the provided slides and images, adding definitions, examples, and tables for clarity and completeness.