Ecosystem Ecology

Basic ecosystem - nutrient cycling in red, energy flow in grey

Basic Energy Flow

Basic Energy Flow

Energy Flow Expanded

Energy Flow in Different Ecosystems

Transfer Efficiency

10% Rule for Transfer Efficiency

Consumption Efficiency• CE = food ingested/food produced

• How much of prey population that consumer eats

• For herbivores – 5% in forests, 25% in grasslands, 50% in phytoplankton ecosystems

• For vertebrate predators – up to 50-100% vertebrate prey; 5% invertebrate prey

• For invertebrate predators – 25% invertebrate prey

Assimilation Efficiency

• AE = food assimilated/food ingested

• How much of prey eaten is digested

• AE usually low for herbivores, microbivores, detritivores – 20-50%

• AE usually high for carnivores – 80%

Production Efficiency

• PE = new biomass produced/food assimilated

• How much of prey digested is converted to consumer biomass and used in reproduction – rest is lost as respiratory heat

• PE high for invertebrates – 30-40%

• Intermediate for ectotherm vertebrates – 10-20%

• Low for endotherm vertebrates – 1-2%

For Example – Caterpillar Efficiency

Efficiency of Energy Transfer (Production Efficiency)

E = P/(P + R)

where

E = efficiency

P = net production

R = respiration

• Some representative efficiency values are as follows:

• birds 1.3%

• small mammals 1.5%

• large mammals 3.1%

• fish 10.0%

• herbivorous insects 39%

• carnivorous insects 56%

• detritivore insects 47%

Lindeman’s Efficiency

• LE = assimilation at trophic level n

assimilation at trophic level n – 1

LE examines efficiency of transfer between trophic levels – often assumed to be 10% but…is actually more complex

Light Absorption

Lindeman’s Efficiencies

Decomposition

Decomposition

• Role in ecosystems – decomposition is gradual disintegration of dead organic matter and is brought about by both physical and biological agents

• decomposers - organisms which convert organic elements to inorganic form - mostly bacteria and fungi

• detritivores - animals that consume dead organic matter

• only decomposers can break down complex organic material releasing nutrients to soil - other organisms can do limited breakdown, but not enough to efficiently recycle nutrients

Resources for decomposers and detritivores

• not just dead bodies of plants and animals, but also shed dead body parts such as skin cells (food for mites on humans), feathers, horns, leaves, twigs

• loss of cells from root caps creates rhizosphere which is resource rich place for soil bacteria

• plant tissues are leaky and release soluble sugars and nitrogen compounds on leaf surface creating rich environment for bacteria and fungi on leaves called phyllosphere

Rhizosphere

Rhizosphere

Bacterial Cells in White, Green, Red

Phyllosphere

Phyllosphere

Phyllosphere – Bacteria from Leaf Impressions on Plate

Donor Control

• Decomposers and detritivores live in world where resource supply is donor controlled - the donor controls density (population size) of the recipient, but the reverse does not happen - there is no direct feedback between consumer population and resource

• In contrast, plants and predators do exert a direct effect on their resources because they reduce amount of resources (population size of the prey) in the environment

Basic Energy Flow

Important Terms for Decomposition Cycle

• Immobilization - inorganic nutrient element is incorporated into organic form, usually through the growth of green plants - thus not available to other plants

• Mineralization - conversion of elements from organic to inorganic form by decomposition

Decomposition of Leaves

DecomposersAnd

Detritivores

Detritivore Microfauna

Nematodes Rotifers

Detritivore Mesofauna

Mites

Springtails

Macro-fauna - African dung beetle

Otzi the Iceman

African white-backed vulture

African vultures – Masai Mara

BuryingBeetles

Earthworms

Earthworm casts recycle organic matter in soil

Nightcrawlers are new to North America

Composting

Compost Pile Food Web

Soil Food Web Microbes