Ecosystems

- Ecosystem: The biotic and abiotic parts of an environment and the interactions that occur between them. 
→ e.g., African Savannah, garden pond.

- Biotic: Living
→ e.g., fish, insects.

- Abiotic: Non-living
→ e.g., sunlight, rocks.

- Habitat: Places where specific organisms live.
→ e.g., a tree or pond.

- Population: All the organisms of a particular species found in an ecosystem at any one point in time.

- Community: The population of all species found in a particular ecosystem at any one time.

- Interdependence: The degree to which each population depends on the other.

Natural vs. Artificial Ecosystems:

- Natural ecosystems generally have high biodiversity, a variety of food throughout the year, and different levels of shelter.
- Artificial ecosystems generally have low biodiversity.
- All ecosystems are self-supporting; all they need is an input of energy, which is usually sunlight.

Food Chains and Webs

- Trophic level: A specific feeding position within a food chain.
- Carnivore: An animal that eats other animals.
- Herbivore: An animal that eats plants.
- Omnivore: An animal that eats plants and animals.
- Apex predator: Top of the food chain, has no predators.

Food Webs (what's happening in a habitat):

Example:

Pyramids

Pyramids of Numbers:

e.g.

- These don't take into account how big things are, ∴ they are unrepresentative.

Pyramids of Biomass:

- Always pyramid-shaped.
- We use the dry mass of an organism to construct a pyramid of biomass; however, the wet mass can vary significantly.
- This implies that gathering and killing organisms is necessary for data collection. The use of options and estimates is unethical.
- There are many problems collecting data. For instance, the mass of a deciduous tree varies significantly from summer to winter.

e.g.

- Make sure the heights of the bars are all equal and the lengths are proportionate to the scale.

Transferring Biomass

- Biomass will always decrease down a food chain.

- Producers (photosynthetic producers) increase their biomass by photosynthesising.
- They use energy from the sun to create food, which is an energy source.
- Producers can only transfer 1% of the light energy that reaches them to biomass.

- Only a small portion of what we (animals) eat actually contributes to growth.

Biomass Loss Includes: (most eaten biomass wasted)

1) Egestion
2) Respiration: To stay alive, the organism uses a significant portion of its energy for respiration. It doesn't store this energy, and it releases a significant amount of it as heat.
3) Some animal biomass is not eaten/digested—e.g., bones.

- Herbivores consume a significant amount of food, much of which is indigestible due to its high fibre content.
- Carnivores can digest much more of their food, so they don't eat as often.
- The more an animal moves, the more it respires, and the more biomass is lost.
- Warm-blooded animals respire even more to maintain body temperature, so their biomass loss is increasing.

Protein:

- If an animal eats excess protein, it cannot store it.
- Urine loses excess protein when it converts to urea.
- Urea is an energy-containing molecule.
- Excretion of urea also contributes to biomass loss.

- The diagram indicates a 10% energy transfer between trophic levels, although this can naturally vary.
- Due to the large losses involved, food chains rarely have more than five trophic levels.
- The lost biomass cannot sustain another organism or population of organisms.

Energy Efficiency Calculations:

Competition

- Every organism competes with other organisms for resources.
→ Successful competitors survive; others die.

What Plants Compete for?

- Water: Used in photosynthesis and to cool the plant. A large tree would absorb most water in the soil, leaving little for smaller ground plants.
- Light: Energy supply for photosynthesis. The tree leaves absorb some light, and not much light passes through. ∴ It's too shady under a tree for most plants to grow.
- Soil minerals: Needed to keep plants healthy. A big tree can absorb far more minerals than small plants.
- Space: The tree roots take up most of the space in the ground, leaving little room for ground plants. 
- CO₂ (rare): Massive canopies of tree leaves absorb CO₂, so less is available under the tree for ground plants.

What Do Animals Compete for?

- Food and water
- Space/breeding territories
- Mates

Ecological Niche:

- The role of an organism within an ecosystem.
- It's crucial for species to occupy distinct niches, as the competition between two similar species can lead to a decline in the population of one of them.
→ e.g., red and grey squirrels

- Interspecific competition: Between organisms of different species.
- Intraspecific competition: Between organisms of the same species competing for everything in their niche.

Examples:

1) Why do farmers/gardeners remove their weeds?
→ This prevents competition for the resources that the plants require.
2) Why do bluebells only grow in spring in British woodlands? 
→ They're in competition for light before their leaves have fully grown back.

Summary

Intraspecific Competition:

- Food is a limited resource. If the population increases, there will be a shortage of food, leading to starvation deaths.
- Some animals have access to food, which ensures sufficient breeding behaviour.
- Territorial animals compete with others to obtain defined territorial areas. Territorial animals force the losers to migrate in search of a less crowded habitat.

Interspecific Competition:

- There may be competition for food; predators may have the same prey.
- Plants compete for light, water, and minerals from soil.
- Competition may lead to the elimination of weaker species or to both species coexisting in smaller numbers.
- No two species in nature have the same requirements, which limits competition. Each species has its own ecological niche in the ecosystem.

Predator and Prey

Characteristics - Prey:

- Have large numbers of young, as many are likely to be killed.
- Adopt a herd lifestyle to reduce the likelihood of discrimination.
- Speed
- Monocular vision
- Simultaneous birth of the young reduces the risk of everyone dying.
- Camouflage

Characteristics - Predator:

- Binocular vision
- Strength and speed
- Camouflage to prevent detection when stalking.
- They use their large teeth and claws to hold and kill.
- Small number of young.
- Some have stinging poison.
- A keen sense of hearing and smell is essential for detecting prey.
- Hunt in a pack or alone using stealth.

- The populations of predators and prey are dependent upon each other and directly affect each other.

- This cycle can be plotted on a graph, using one line for each population.

- It's important there are no other predators in this habitat to see the predator-prey cycle.

Mutualism:

- This is a situation where two species coexist and both species reap benefits.
→ e.g., bees and flowers

Species Distribution in a Habitat:

- Abundance: How many organisms of a species there are.
- Distribution: Varying organisms are dispersed.
- Zonation: Gradual change in an abiotic factor in an ecosystem.
- Abiotic and other biotic factors determine abundance, distribution, and zonation.