10 IB Biology

Ecology

study of the interactions among organisms and with their environment.

Scientists who study ecology are called ecologists.

Ecosystems

An ecosystem consists of the physical environment, and all the living things within that environment.

Abiotic Factors: these are the non living things that make up the physical environment.

Examples: water, atmosphere, soil, temperature

Biotic Factors: these are the living things within the physical environment.

Examples: plants, animals, fungi and bacteria

Types of Ecosystems

Terrestrial Ecosystem

An ecosystem contained on land

Located on continents of islands, water is a limiting factor

Aquatic or Marine Ecosystem

An ecosystem contained in water

Freshwater - lakes and rivers

Saltwater/Marine - oceans

Trophic Levels

All living things have a part to play in the function of an ecosystem. These roles are defined by trophic level.

The trophic level of an organism is defined by the energy and nutrients it contributes, consumes or recycles within the ecosystem.

Autotrophs and Heterotrophs

Organisms need nutrients like carbon compounds (e.g., glucose) to survive. Autotrophs (producers) make their own carbon compounds from carbon dioxide and water, while heterotrophs (consumers) get them by eating other organisms. Some unicellular organisms, like Euglena, can use both methods.

Roles in Ecosystems

Autotrophs (producers like plants and algae) capture sunlight and turn it into energy

heterotrophs (like primary, secondary, and tertiary consumers) get their energy by eating other organisms.

Omnivores eat both producers and consumers.

More Complicated Roles

Detritivores - heterotrophs that obtain nutrients from detritus by internal digestion.

Decomposers - consume dead plant and animal remains and convert them into substances that can be reused.

Scavengers - eat dead animal remains in order to obtain energy.

Saprotrophs - heterotrophs that obtain nutrients from dead organic matter by external digestion.

Energy in Ecosystems

Most ecosystem rely on the sun to supply energy.

This energy is harvested by living organisms through the process of photosynthesis.

Photosynthesis is performed by autotrophs such as plants, eukaryotic algae and cyanobacteria.

Heterotrophs do not use light energy directly but are indirectly dependent on it.

Heterotrophs use carbon compounds as a source of energy, carbon compounds originate in producers through photosynthesis.

Photosynthesis

Producers absorb sunlight and convert it into chemical energy through photosynthesis, using it for their own activities, with energy lost as heat, and the remaining energy is available to heterotrophs.

Energy flow in Ecosystems

Energy flows through a food chain, starting with producers, and is used by organisms to make ATP, with some energy lost as heat along the way.

Energy Losses in Ecosystems

When an organism consumes energy, only 10% of it gets passed on to the next level in the food chain, while the other 90% is used for energy and lost as heat, meaning less energy is available as you move up the food chain.

Ecological Pyramids

Visual representations of the populations involved in a feeding relationship.

There are three types of ecological pyramids:

Pyramid of numbers

Often counting organisms is used to determine the flow of energy through an ecosystem.

This type of diagram shows that the relative number of organisms decreases as we move up trophic levels.

Not always pyramid shaped.

Pyramid of biomass

It is possible to estimate the mass (in grams) of all the organisms living in a given area or ecosystem.

This estimation is known as the biomass.

A pyramid can be constructed showing that the biomass of the producers is generally far greater than that of the consumers.

Pyramid of energy

A pyramid of energy is used to represent the amount of energy converted to new biomass by each trophic level in an ecological community.

Measured in units of energy per unit area per unit time: kJ m-2 y-1.

Food Webs

An organism's trophic level is its feeding position in a food chain.

However, feeding relationships in ecosystems are complex and an organism can occupy more than one trophic level.

A food web is a model that summarizes all the possible food chains in a community.

Within a food web there are often one or two organisms that have no predators.

These organisms are known top carnivores and are usually found at the top of the food web.

Humans are not considered top carnivores within any ecosystem.

Atypical Feeding Relationships: Symbiosis

These relationships do not involve one species "eating" another.

There are three common types of symbiotic relationships:

Mutualism

Commensalism

Parasitism

Mutualism

both organisms benefit

Commensalism

an organism benefits the other is neutral

Parasitism

One organism benefits and the other is harmed

Interactions among Species in an Ecosystem

A species is a group of animals that can have babies together

a population is a group of the same species living in one place

a community is all the different populations living together

a niche is how a species lives and interacts with others in its environment.

Population Growth

If a population experiences ideal conditions the resulting

population growth over time will be exponential. This produces

the "J" shaped curve on a graph.

This indicates exponential growth.

However, when a population colonizes a new area the growth curve produced is a sigmoid or "S" shaped curve. The environment will eventually limit the growth of the population.

Carrying Capacity

The carrying capacity of an ecosystem is the maximum number of individuals that can live there, based on factors like food, space, and other resources.

Limits to Growth

Limiting factors are things that affect how big a population can get, and they include:

Materials and Energy - like water, food, and energy.

Food Chains - the number of organisms depends on those below it in the food chain.

Competition - when animals or plants fight for resources.

Density - how many individuals are in a certain area.

Explaining a Population Growth Curve

At first, the population grows quickly because there are few limiting factors, with more births than deaths. As the population gets bigger, limiting factors slow growth, and the mortality rate increases. Eventually, the population reaches a balance where birth and death rates are almost the same, which happens near the environment's carrying capacity. At this point, immigration (more individuals moving in) increases the population, while emigration (moving out) decreases it.

Competition

When looking at competition it is important to distinguish between the 2 types of competition seen in an ecosystem.

Intraspecific Competition - competition between members of the same species

Interspecific Competition - competition between member of different species

The Niche concept

For a species to survive, the abiotic factors (like temperature and water) must be right, and all the species it needs to interact with must be present. If two species have the same niche in the same habitat, they can't both survive forever because they will compete for the same resources, which is called the competitive exclusion principle.

Competitive Exclusion Principle

This was demonstrated in experiments on Paramecium

by Carl Friedrich Gauss. He cultured two species individually under ideal conditions to determine the expected biomass of that species.

Next, the two species were cultured together under the same conditions and both species declined but one declined much more than the other.

Carl Gauss showed that when two species of Paramecium were grown together, one outcompeted the other, supporting the competitive exclusion principle.

Fundamental and Environmental Niche

The fundamental niche is the potential way a species could live based on its adaptations, while the realized niche is how the species actually lives, shaped by both its adaptations and competition with other species.

Density

Limiting factors can be density dependent or density independent.

Density Dependent Limiting Factors

These are factors that affect populations as the population size increases.

Examples include disease, aggression, stress.

Density Independent Limiting Factors

These are factors that affect populations regardless of size. Examples

include flood, fire, tornado, hurricane.

Carbon

Carbon is the building block of all life because of these four key features:

It has 4 available binding sites to form bonds.

It can form single, double, or triple covalent bonds.

It can bond with many different elements.

It can form long chains or rings of atoms, allowing for complex structures.

Carbon Fixation

Carbon is found in the atmosphere as carbon dioxide (CO2). Autotrophs like plants take in CO2 and convert it into carbohydrates, lipids, and other organic compounds through photosynthesis. This creates a concentration gradient where the inside of the autotroph has less CO2 than the outside, so CO2 diffuses into the plant. The process of photosynthesis is represented by this equation:

6 CO2 + 6 H2O + sunlight → C6H12O6 + 6 O2.

Aquatic Carbon

In aquatic ecosystems, carbon enters in two ways: