ecology section D

Factors which influence the numbers and types of organisms within an ecosystem

Abiotic factors:
non-living factors
examples: include ~ light intensity, temperature, exposure, soil type, altitude, % humus, dissolved oxygen, wind

biotic factors
living factors ~ the influences of living organisms on each other

examples include:

feeding- more animals can live where there are more plants, which provide food and shelter

competition- tends to reduce organism numbers

predation- tends to reduce the number of prey

pollinators- a decrease in the bee population, means less pollination and fewer seeds produced, so a decline in the plant populations

disease- reduces populations, for example myxomatosis 1950s

climate factors

influence of prevailing weather conditions on living organisms

temperature- organisms grow best at higher temperatures as chemical reactions are faster, but lower temperatures cause some animals to hibernate

light intensity- plays a major role in plant distribution as controls the rate of photosynthesis
e.g buttercup grows better where there is strong exposure to the sun, whereas bluebells grow better best in a shaded woodland

wind exposure- trees grow best on sheltered side, wind aids seed dispersal e.g. grass

edaphic factors

are edaphic factors relating to the soil

examples
-soil type
-soil ph- most plants prefer neutral to slightly alkaline soils
-minerals content- plants absorb minerals in solution, so if there is insufficient water, soluble minerals are not available
-humus content

aquatic factors:

factors relate to organisms living in or near water based environments such as the rocky seashore

examples

• wave action and currents- waves create currents which can plants and animals away, Seaweeds and mussels have structures for attachment to rocks

• light penetration- as water interferes with light penetration, plant life is very much limited to the brightly lit upper layers of lakes, rivers, seas

• dissolved oxygen concentration- oxygen is needed for aerobic respiration

Energy flow

energy flow- the pathway of energy transfer

ecosystems are unable to function unless there is a constant input of energy from an external source

• the sun is the primary source of energy for our planet

• only 1% of energy from the sun is trapped by plants

• sunlight energy is converted to chemical energy by green plants through photosynthesis

• plants or producers transfer chemical energy to consumers during feeding

• 10% of chemical energy is transferred as energy transfer involves great wastage:
  - as energy is lost and used in growth, respiration or lost as heat energy

Different types of nutritional types

organisms are divided into two major nutritional types
producers
consumers

producers:
make their own food using an energy input. Carry out photosynthesis
examples:
green plants are photosynthetic, using sunlight energy to make carbohydrates
chemosynthetic bacteria make food using energy from chemical reactions

consumers:

cannot make their own food and take in food from another organism

types of consumers

herbivore- only eats plants
adapted to eating plants as they have ridged teeth to crush grass and cows and sheep have long intestines with bacteria to digest cellulose
e.g. cows sheep rabbit

carnivores- only eat meat called the secondary consumers when they feed on the primary consumer or tertiary consumer if they feed on the secondary consumer

omnivores- eat both plants and animals
have a range of adaptations e.g. humans have different enzymes to digest different food types
e.g. humans gulls, badgers, crows

decomposers- feed on dead organic matter usually by extracellular digestion
cause- nutrient recycling
e.g. earth worms

detritus feeders:
consume decaying plant and animal parts as well as faeces

Food chains

a list of species such that each species in the list is eaten by the next one

it is a pathway along which energy is passed from one species to another, through feeding, with one species at each trophic level

grazing vs detritus food chains

grazing food chains begin with green plants
detritus food chains begin with detritus which is dead or decaying organic matter in the soil

Trophic levels

the feeding or energy level in a food chain
marks the position of a species within a food chain

Grassland food chain

• grazing food chain starts with a green plant and is the most common:
  buttercup → greenfly → ladybird → blackbird

• the arrow connects each step in the food chain and represents the direction of energy flow

• food chains are normally short with 4/5 feeding levels as:
  1. only 10% energy is passed on to the next feeding level
  2. there is a large energy loss 90% at each level due to growth, respiration and lost as heat energy

detritus food chain

detritus → earthworm → thrush → hawk    

• detritus is composed of a mixture of non-living organic matter and attached to micro-organisms: e.g. decaying leaves, animal remains, manure

• decomposers such as bacteria and fungi decompose dead plants and animals

• products of decomposition: are leaves are consumed by detritus feeders and then on to carnivores

aquatic ecosystem food chain
phytoplankton → zooplankton → sea trout → seal

producer: leaves
primary consumer: snail, earthworm, green fly, rabbit
secondary consumer: stoat, ladybird, hedgehog
tertiary consumer: fox

pyramid of numbers: a pyramid of numbers is a diagram which shows the number of different organisms at each trophic

general features of a pyramid of numbers

Limitation of use of pyramid of numbers

ecological pyramid may be defined as a way of comparing different communities of the ecosystem, in order of different trophic (feeding) levels

Pyramid of numbers

1. they do not take into account the size of the organisms:
   e.g. a single oak tree can support thousands of greenfly
   - results in an inverted pyramid

2. sometimes the pyramid cannot be drawn to scale due to large numbers of organisms
   eg thousands of flea feeding on a fox
   - results in a parasitic or distorted pyramid

niche

the ecological niche is the functional role of an organism in an ecosystem.
e.g. what it eats and who feeds on it, how it interacts with different organisms

why most species try to occupy different niches

1. two species with the same niche cannot survive for long in the same habitat

2. as there is too much competition for space, food, mates

3. so the better adapted species will survive at the expense of the less well adapted

4. therefore, most organisms will try to occupy different niches within the same habitat, to survive
   eg swallows feed on flying insects, thrush feeds on ground insects on trees and fruit