Tropical community ecology midterm 1

What is a biological community?

A level of biological organization made up of interacting populations of different species in the same area

Collective properties

Simple sum of all parts of a community

Examples of collective properties

Species richness; biomass

Emergent properties

Properties that are more than the sum of all parts

Examples of emergent properties

Niche partitioning; density-dependent predation; food web structure

Community structure

How a community looks

Community function

What happens in a community (processes)

Community composition

Which species are present

Tropical forest emergent layer

Tallest trees receiving the most sunlight

Tropical forest canopy

Main layer formed by tree crowns

Tropical forest undercanopy

Lower branches beneath the canopy

Tropical forest shrub layer

Small plants on the forest floor

Habitat structure factors

Carbon storage; light availability; age/size distribution; successional stage; microhabitats

Main drivers of habitat structure

Latitude; altitude; moisture

Guilds / functional groups

Groups of species that use resources in similar ways

Community functions

Nutrient cycling; carbon sequestration; erosion control

Local community assembly processes

Dispersal; abiotic factors; species interactions

Metacommunity

A group of communities that interact with each other

Clements view of communities

Communities act as tightly coevolved superorganisms

Gleason view of communities

Communities assemble loosely based on species tolerances and chance

Examples of bounded communities

Ponds; mangroves; bromeliads; tree-fall gaps

Why the tropics receive more energy

Earth's shape causes uneven heating concentrated at the equator

ITCZ

Low-pressure belt near the equator where trade winds converge and cause rainfall

Cause of wet and dry seasons in the tropics

Seasonal movement of the ITCZ

Why biodiversity is higher in the tropics

Less temperature variation and consistent solar energy

Effect of altitude on tropical temperature

Temperature decreases with increasing altitude

Orographic effect

Air rises over mountains, cools, condenses, and causes rain

Köppen climate maps

Classify biomes based on climate

Holdridge life zone system

Classifies communities using temperature, precipitation, and biotemperature

Biotemperature

Temperature as experienced by plants for photosynthesis

Potential evapotranspiration (PET)

Balance between water gained and water lost

PET greater than 1

More water lost than gained

Gross Primary Productivity (GPP)

Total energy captured by plants per unit area per time

Net Primary Productivity (NPP)

GPP minus respiration

Why NPP is hard to measure

Belowground growth, herbivory, and root exudates are difficult to quantify

Highly productive ecosystems

Coral reefs; algal beds; swamps; marshes; mangroves

Why tropical forests are "leaf factories"

Most productivity occurs in leaves rather than wood

Leaf litter in tropical forests

Dropped year-round in very large amounts

Dominant tropical soil types

Oxisols and Ultisols

Why tropical soils are nutrient-poor

Heavy weathering and leaching remove nutrients

Paradox of tropical luxuriance

High biomass and productivity on nutrient-poor soils

Where nutrients are stored in tropical forests

Plants and leaf litter rather than soil

Plant adaptations to low soil fertility

Shallow roots; more roots; tougher leaves; longer leaf lifespan

Importance of decomposition in the tropics

Rapid nutrient recycling maintains productivity

Key decomposers in tropical forests

Bacteria; fungi; termites; invertebrates; protists

Energy flow vs matter cycling

Energy flows through ecosystems; matter cycles within them

Why ecosystems are open systems

They exchange energy and matter with surroundings

Limitation on food chain length

Energy loss at each trophic level

Net Production Efficiency (NPE)

Efficiency of converting energy into biomass

Endotherms vs ectotherms

Endotherms lose more energy as heat

Bottom-up control

Plant defenses limit herbivore populations

Top-down control

Predators limit herbivores and protect plants

Trophic cascade

Chain reaction caused by removal of a species

Connectance

Actual interactions divided by possible interactions in a food web

Keystone species

Species with a disproportionately large effect on ecosystem structure

Typical tropical food chain length

Short (about four trophic levels)