unit 3

Population – A group of individuals of the same species living in the same area.
Exponential population growth – Growth with no limits; population increases rapidly.
Logistic population growth – Growth that slows as population reaches carrying capacity.
Community – All the interacting species living in the same area.
Interspecific competition – Two species compete for the same resources (–/–).
Predation – One organism kills and eats another (+/–).
Herbivory – An animal eats plants (+/–).
Mutualism – Both species benefit (+/+).
Parasitism – One organism lives on/in another and steals nutrients (+/–).
Ecological niche – A species’ “role” in its environment: habitat, diet, activity, and interactions.
Producers – Organisms that make their own food (plants, algae).
Primary consumers – Herbivores that eat producers.
Secondary consumers – Carnivores that eat herbivores.
Tertiary consumers – Top predators that eat carnivores.
Species diversity – The variety and relative abundance of species in a community.
Ecosystem – A community plus the nonliving environment.
Carbon sink – Anything that absorbs more carbon than it releases (forests, oceans, soil).
Animal – A multicellular heterotroph that ingests food.
Ingestion – Taking food into the body to digest internally.
Endoderm – Inner tissue layer; forms digestive system.
Mesoderm – Middle tissue layer; forms muscles and organs.
Ectoderm – Outer tissue layer; forms skin and nervous system.
Molting – Shedding an exoskeleton to grow.
Exoskeleton – Hard outer skeleton that protects and supports the body.
Radial symmetry – Body arranged around a central axis (like a jellyfish).
Bilateral symmetry – Left and right mirror halves (most animals).
Segmentation – Body divided into repeating units.
Metamorphosis – A developmental change from juvenile to adult form.

🧬POPULATION ECOLOGYWhat is a population?

A population is a group of individuals of the same species living in the same place at the same time.

Recognizing the graphs

  • Exponential growth: J-shaped curve.

  • Logistic growth: S-shaped curve.

  • Carrying capacity: The flat upper region where the logistic curve levels off.

When does exponential growth occur?

When resources are unlimited and the population is small or newly introduced.

When does logistic growth occur?

When population size is limited by food, space, disease, competition, etc. (density-dependent limits).

What is more common in nature?

Logistic growth — because natural resources are limited.

Density-dependent factors

Factors that get stronger as population size increases:

  • Competition

  • Disease

  • Predation

  • Food shortage

  • Crowding stress

Density-independent factors

Affect populations regardless of size:

  • Weather

  • Natural disasters

  • Pollution

  • Drought

  • Temperature extremes

🌿COMMUNITY & ECOSYSTEM ECOLOGYWhat is an ecological community?

All the interacting species in a given area.

What is an ecosystem?

A community plus the non-living environment (air, soil, water, climate).

Identifying trophic levels

  • Producers: Plants, algae

  • Primary consumers: Herbivores (rabbits, zooplankton)

  • Secondary consumers: Carnivores that eat herbivores (snakes, small fish)

  • Tertiary consumers: Top predators (hawks, sharks)

Which trophic level has the highest biomass?

Producers — because energy is lost as it moves up the food chain.

Lowest biomass?

Tertiary consumers — least energy available to them.

Carbon cycle basics

Removed from atmosphere by:

  • Photosynthesis (plants, algae)

Added to atmosphere by:

  • Cellular respiration (all organisms)

  • Decomposition

  • Burning fossil fuels

  • Deforestation

What is a carbon sink? Why important?

A carbon sink is a long-term storage site for carbon (forests, soil, oceans).
They slow climate change by reducing atmospheric CO₂.

How farming disrupts nitrogen & phosphorus cycles?

  • Fertilizer use adds excess N & P

  • Runoff moves nutrients into lakes and rivers

  • Soil is depleted when crops are removed each harvest

What is eutrophication?

A nutrient overload (N & P) causes algal blooms; when algae die, decomposition removes oxygen, killing fish.

Relationships (+/– chart)

  • Predation: +/–

  • Herbivory: +/–

  • Mutualism: +/+

  • Parasitism: +/–

  • Competition: –/–

What is an ecological niche?

Everything a species needs and does: habitat, food, behavior, timing, interactions.

What happens when niches overlap?

Competition; one species may outcompete the other, or they may partition resources.

Difference between parasitism and predation

Parasitism steals nutrients without killing immediately; predation kills quickly for food.

🐾ANIMAL PHYLA & BODY PLANSFour key body plan features (used to build the animal evolutionary tree):

  1. Tissues (none / two / three)

  2. Symmetry (none / radial / bilateral)

  3. Protostome vs. deuterostome

  4. Molting (ecdysis)

What are tissues? How many layers do animals have?

Tissues are collections of specialized cells.
Most animals have three layers: ectoderm, mesoderm, endoderm.

Radial vs. bilateral symmetry

  • Radial: Body organized around a central axis (cnidarians).

  • Bilateral: Left and right sides mirror each other (most animals).

Most animals have bilateral symmetry.

Protostome vs. deuterostome

  • Protostomes: Mouth develops first (arthropods, mollusks, annelids).

  • Deuterostomes: Anus develops first (echinoderms, chordates).

🐚ANIMAL PHYLA (Descriptions + Examples + Traits)Porifera (Sponges)

  • No tissues, no symmetry.

  • Filter feeders.

  • Ecological role: clean water.

Cnidaria (Jellyfish, sea anemones)

  • Radial symmetry; stinging cells.

  • Two tissue layers.

  • Ecological role: important predators.

Platyhelminthes (Flatworms)

  • Bilateral, soft-bodied, no body cavity.

  • Includes tapeworms and planaria.

  • Many are parasites.

Mollusca (Clams, snails, octopus)

  • Soft bodies, often with shells.

  • Bilateral; protostomes.

  • Ecological role: food sources, filter feeders.

Annelida (Earthworms, leeches)

  • Segmented bodies; bilateral.

  • Protostomes; no molting.

  • Ecological role: soil aeration.

Arthropoda (Insects, spiders, crustaceans)

  • Segmented, jointed legs, exoskeleton.

  • Protostomes; they molt.

  • Ecological role: pollinators, decomposers, predators.

Which animals belong to each phylum?

  • Porifera: sponges

  • Cnidaria: jellyfish, sea anemones

  • Platyhelminthes: tapeworms, planaria

  • Mollusca: clams, oysters, snails, slugs, octopus

  • Annelida: earthworms, leeches

  • Arthropoda: insects, spiders, crabs, shrimp, lobsters, millipedes, centipedes

🌟GENERAL QUESTIONSSexual vs. asexual reproduction

  • Sexual: two parents, produces genetically unique offspring.

  • Asexual: one parent, identical offspring.
    Doing both is beneficial because it allows fast reproduction and genetic diversity.

What is metamorphosis? Why is it useful?

Metamorphosis is a dramatic change in body form from juvenile to adult.
It reduces competition because larvae and adults use different resources.

What is a parasite?

An organism that lives in or on a host and steals nutrients (+/–).

What is segmentation? Which phyla have it?

Segmentation means the body is divided into repeated units.
Seen in Annelida and Arthropoda.

What is an exoskeleton? Which phylum has it?

A hard external skeleton for protection and support.
Found in Arthropoda.