Communities

Rarefaction Curves

Most species are rare; very few species are common

Ecological Niches

Every organism has a set of environmental parameters that they can live in

Ex. Temperature, humidity, color, etc.

Fundamental Niche

Full spectrum of all environmental conditions

Realized Niche

The actual environmental conditions they can live in

Barnacles

If two organisms have the same niche, they cannot live in the same place

Competitive Exclusion

Multiplicative growth, but they must hit carrying capacity. If they both have the same niche, only one can occur there, and the other goes extinct.

• Ex. Neanderthals

Resources Partitioning

Species that all use the same habitat, but different parts of it

Character Displacement

Two sympatric species with broadly overlapping distributions of resource use

Community Composition

What enables species to coexist

• Species evenness: Most species in most communities are rare

  Ex. Salt Marshes - species-poor

  Ex. Fens - species-rich

Competitive Exclusion vs Resource Partitioning

Competitive exclusion involves species that have the same niche, while resource partitioning refers to species that fill different niches in a habitat.

Body Size and Tropic Level

Most species are small - advantageous to have a large body mass because it’s lower metabolism per unit pass + large individuals eat larger prey and escape predation

• Larger population densities → reduced extinction risk

Energy

Only 2% of the usable light that hits the planet is absorbed by plants, 98% gets frittered away

GPP: Gross Primary Productivity

All the light that is converted to biomass

NPP: Net Primary Productivity

Light that is passed from plants to herbivores and all other trophic levels of heterotrophs

1st Level: Respiration

2nd Level: Primary Consumer (Herbivores)

3rd Level: Secondary Consumers

4th Level: Apex Predators

Trophic Pyramid

• 90% energy loss at each trophic level

• Big animals are rare because there’s barely any energy at that level

• Free-living herbivores are more abundant, predators of herbivores, and then predators of predators

Tropics: Evaporation + Transpiration

The Hotter it is, it gets too hot for productivity to occur. However, if there's an increase in water, there's a latitudinal gradient that tells us about where species occur and where species diversity changes on the plant

Janzen-Connel Hypothesis

The probability of seed dispersal decreases as distance from the parent plant increases

• Insect herbivores only ate seeds of specific trees

• High predation rates in areas w/ high seed fall

High Equilibrium Diversity in Tropics

a) Climatic stability

i. allows specialization, tighter niche packing

ii. new niches

b) Biotic Interaction: Stable climate → more predators and pathogens → numerical dominance of best competitors

c) Productivity: Increases toward equator; allows more specialization

Swallowtail Diversity

Increasing levels of specialization towards the tropics that allows more species to co-occur

Carnivore Loss Around the World

• Habitat loss, human interactions, no prey to hit on

• Predators don’t mix with livestock

Intermediate Disturbance Hypothesis

• At low levels of disturbance, you get a few species b/c the best competitors take over

• At high levels of disturbance, there aren’t many species b/c the species that are there are really good at colonizing disturbed habitats

  • Highly disturbed: Small boulders, Low Disturbance: Big Boulders, Medium Disturbance: Medium Boulders