ECOSYSTEMS

What is an Ecosystem? The biological community together with its associated non-living environment Ecosystems consist of biotic and abiotic components

Biotic Components of an Ecosystem Living things Divided into two groups based on their source of food: Autotrophs Heterotrophs

Autotrophs Require only inorganic nutrients and an outside energy source to produce organic nutrients Also called producers as they produce food Two types: Photoautotrophs – produce organic nutrients via photosynthesis Chemoautotrophs – produce organic nutrients using energy obtained from the oxidization of inorganic compounds

Examples of Autotrophs Cyanobacteria Photosynthetic protists Plants Algae Chemosynthetic bacteria

Parasitic herb (Hyobanche sanguinea), Namaqualand Heterotrophs Require a source of preformed organic nutrients Also called consumers as they consume food All animals are heterotrophs, as are fungi, many bacteria and parasitic plants Parasitic herb (Hyobanche sanguinea), Namaqualand

Types of Heterotrophs Herbivores – Feed on plants or algae Carnivores – Feed on other animals Omnivores – Feed on plants and animals Detrivores – Feed on decomposing organic matter Decomposers – Break down organic material

Examples of Heterotrophs Herbivore Herbivore Carnivore Carnivore Decomposer Decomposer

Energy Flow & Chemical Cycling Every ecosystem is characterised by two fundamental processes: Energy flow One-way flow of energy through biotic community Begins when producers absorb solar energy Chemical cycling Cyclical flow of materials from the abiotic environment, through the biotic community and back again to the abiotic environment

Energy Flow & Chemical Cycling Energy flows through an ecosystem Chemicals cycle through an ecosystem

Energy Flow With few exceptions, all ecosystems depend on solar energy as a primary energy source Primary productivity is the rate at which producers convert solar energy into biomass Primary productivity is dependent upon sunlight, nutrient and water availability

Productivity of Ecosystems Tropical rain forests have high productivity because of abundant rainfall and sunlight Estuaries and marshes have high productivity because of high nutrient influx from rivers and streams

Productivity of Ecosystems

Energy Flow Some of the energy captured from the sun is lost to the environment as heat when producers use energy for cellular respiration Some energy also goes to detritus feeders through waste production and death Only a portion (~10%) of the energy captured by producers is passed on to consumers

Energy Flow Consumers also lose energy due to respiration, excretion, and death At each trophic level, only ~10% of the energy is passed up to the next trophic level All the energy taken in by producers is ultimately lost as heat through respiration

Energy Flow Only 10% of the energy taken in by a herbivore goes to carnivores The rest goes to detritus feeders, or is lost to the environment as heat

Energy Flow Energy flow through an ecosystem is one way; it is not recycled Autotrophs must continue to capture the sun’s energy for ecosystems to persist

Trophic Levels Ecosystems have a trophic structure that represents the different feeding relationships that determine the route of energy flow and the pattern of chemical cycling Species in an ecosystem are divided into different trophic levels based on their main source of nutrition

Trophic Levels Trophic levels include: Primary producers Primary consumers Secondary consumers Tertiary consumers Detritivores and decomposers

Primary Producers Autotrophs support all other trophic levels either directly or indirectly by synthesising sugars and other organic molecules using light energy EXCEPTION: In hot water deep-sea vents, chemosynthetic bacteria form the basis of the food chain. These bacteria obtain energy from chemical sources such as hydrogen sulfide (H2S) instead of from sunlight

Primary Consumers Primary consumers are herbivores that consume the primary producers For example, herbivorous insects, grazing mammals, seed-eating birds, aquatic zooplankton and some fish

Secondary Consumers Secondary consumers are carnivores that eat herbivores E.g. spiders, frogs, insect-eating birds, lions, many fish, sea-stars

Tertiary Consumers Tertiary consumers are carnivores that eat other carnivores

Detritivores & Decomposers These are consumers that derive energy from organic wastes and dead organisms E.g. bacteria, fungi, and scavengers such as cockroaches and vultures This level is an important part of the recycling process as it returns chemicals to the primary producers

Food Chains A food chain depicts the transfer of energy from one trophic level to the next

Food Webs Feeding relationships in nature are usually much more complex than a simple chain E.g. several primary consumers may feed on the same plant species and one primary consumer may eat several types of plant These complex feeding relationships are depicted in a diagram called a food web

Antarctic Food Web

Ecological Pyramids Food chains lose energy between trophic levels Only about 10% of the energy of one trophic level is available to the next trophic level This explains why few top carnivores can be supported in an ecosystem The flow of energy between successive trophic levels can be depicted as an ecological pyramid

Productivity Pyramids A productivity or energy pyramid depicts the amount of energy contained in each trophic level from the lowest, the producers, to the highest, the top carnivores Trophic levels are stacked in blocks proportional in size to the energy acquired from the level below

Productivity Pyramid

Biomass Pyramid In a biomass pyramid, each tier symbolises the total dry weight of all organisms in that level

QUESTION Why could more people be supported on Earth if people were vegetarians than if they ate meat?