Ecosystems what are they ?

(Refer to Essentials of Ecology,
G. Tyler Miller)

Ecosystems

Levels of organization

Individual/Organism

Population

Community

Ecosystem

Biosphere

an Ecosystem consists of all of the organisms living in a community (or communities) together with the abiotic factors with which they interact

COMMUNITY

A community / biological community, consists of all the populations of the different species living and interacting in an area. It is a complex and interacting network of plants, animals and microorganisms.Structure of a community is usually the result of many interactions

- competitive interactions (interspecies, intraspecies)

- Symbiosis (mutualism, commensalism, parasitism)

- Predation (predator-prey realtionship; food webs)

- variety of disturbances through time

- environmental fluctuations

Rocky Shore community an example

the mix of barnacles, algal mats, herbivorous snails on rocks etc.predation and competition influence distribution eg. snails grazing algal spores,
predatory snails eating herbivores

Rocky Shore

community

Existence of life depends upon

an energy source (the sun)oxygen, carbon, nitrogen and other elements, all of which are part of worldwide geological and chemical cyclesgravity

An ecosystem consists of 2 major components;

nonliving (abiotic) living (biotic).

The sun

The one-way flow of high-quality energy from the sun, through materials and living things in their feeding interactions, into the environment as low-quality energy (mostly heat dispersed into air or water molecules at low temperature), and eventually back into space as heat. No round trips are allowed because energy cannot be recycled.

Cycles

The cycling of matter through parts of the biosphere is essential to life as the earth is closed to significant inputs of matter from space. So the Earths fixed supply of nutrients must be recycled again and again for life to continue. Nutrient trips in ecosystems are round trips.

Gravity

Allows the planet to hold onto its atmosphere and causes downward movement of chemicals in the matter cycles.

Ecosystem has TWO functions / characteristics

Energy flow

Cycling of materials

Essential characteristics of ecosystems
1. Energy flow

Energy flows in a unidirectional way (it does not cycle!) fig 4.13 Miller Ch 4

This requires a continuous input of energy into an ecosystem

Energy source autotrophs heterotrophs

Essential characteristics of ecosystems
1. Energy flow

Autotrophs

(e.g. plants, algae) organisms capable of synthesizing all their required organic molecules from simple organic substances and an energy source

Heterotrophs

(e.g. animals)

organisms that cannot synthesize complex organic compounds and must feed on organic material formed by other organisms to obtain energy and necessary molecular building blocks for metabolism and growth

Energy in ecosystems

All organisms require energymaintenance, growth, reproduction, (and movement)The energy driving the biosphere (and all ecosystems) is solar radiation, captured via photosynthesis by autotrophsabout 1% of visible light converted to chemical energyabout 120 billion tonnes of new organic material produced each yearabout 99% of all organic matter in the biosphere is autotrophs (i.e. mostly plants)

Primary Production

Photosynthesis

6 CO2 + 12 H2O C6H12O6 + 6 O2 + 6H2O

Respiration

Energy (from photosynthesis) is released and used by the organism when the complex molecules are subsequently broken down during metabolism.

(+ solar energy)

Essential characteristics of ecosystems
2. Cycling of materials

Materials (e.g. carbon, nitrogen, phosphorus) are cycled from the abiotic environment, through living organisms, and back to the abiotic environmentThis results from metabolic activities of plants and animals, and organisms such as bacteria and fungi that break down organic matter

Productivity in ecosystems

A measure of net primary productivity is the change in biomass per unit time
(but be aware of what may have been lost)

Biomass - the weight of living tissue per unit area (e.g. kg/ha)

Which are the most productive ecosystems?

Ecosystem Net primary World primary

production production

(g/m2/yr) (billion t/yr)

Tropical rain forest 2200 37.4

Woodland/shrubland 700 6.0

Temperate grassland 600 5.4

Desert and scrub 90 1.6

Swamp and marsh 2000 4.0

Open ocean 125 41.5

Upwelling ocean zones 500 0.2

Algal beds and reefs 2500 1.6

Miller Ch 4 Fig 4.6

Flow of energy and materials through an ecosystem

Systems approach to ecosystem function

Reading list

Khrone, D.T.(2001). General Ecology. Brooks/Cole Thompson Learning. Chapter 14: Energy Flow and Trophic Structure; Chapter 15: Biogeochemical and Nutrient CyclesMiller, G.T. (2005). Essentials of Ecology. Brooks/Cole Thompson Learning. Chapter 4: Ecosystems: What are they and how do they work?

ECOSYSTEMS

ecosystems are a network of

interactions, beginning with

the PRIMARY PRODUCERS

(the PLANTS) and

connecting to herbivores,

carnivores, parasites,

decomposers

...energy, nutrients & water

are cycled through the

network by these different

groups