Syllabus Edition
First teaching 2024
First exams 2026
Introduction to Ecological Systems (DP IB Environmental Systems & Societies (ESS))
Revision Note
Written by: Alistair Marjot
Reviewed by: Bridgette Barrett
Introduction to Ecological Systems
The biosphere
The biosphere refers to the narrow, life-supporting zone around the Earth
It is where the air (atmosphere), water (hydrosphere) and land (lithosphere) meet
The biosphere contains all living organisms, including:
Plants (flora)
Animals (fauna)
Fungi and microorganisms
It can be thought as one large, complex system of living communities, as well as their interactions with each other and with the non-living components of the Earth's systems, all interacting as a single unit
The biosphere measures approximately 20 km from top to bottom—however, most life exists in a narrow range of 6.5 km (500 m below sea level and 6 km above sea level)
Species
A species is a group of organisms sharing common characteristics that interbreed to produce fertile offspring
This is known as the biological species concept
Members of the same species share a gene pool, meaning that they can breed and produce offspring with similar traits
Populations
A population is a group of organisms of the same species living in the same area at the same time which interbreed
A population can be seen as an interbreeding unit of a species
One species may consist of any number of populations, from one to many—for example:
The Eastern Grey Kangaroo is a species of marsupial native to Australia
This species consists of multiple populations across various regions of Australia
There are populations of Eastern Grey Kangaroos in Queensland, New South Wales, Victoria and other parts of the country
Although individuals from these different populations are capable of interbreeding, in reality they very rarely do due to the fact that they are geographically isolated (separated) from each other
Each population may have its own unique characteristics and adaptations based on local factors such as habitat, climate and food availability
Despite being part of the same species, these populations may exhibit some small genetic and behavioural differences due to their isolation and local environmental conditions
Community
A community includes all of the different populations (of different species) living in the same area at the same time
A community is a collection of interacting populations within an ecosystem
For example, each species within a community depends on other species for food, shelter, pollination, seed dispersal, etc.
Habitat
A habitat is the local environment in which an organism, species, population or community normally lives
E.g. badgers, deer, oak trees and ants are all species that would live in a woodland habitat
A description of the habitat of a species can include both geographical and physical locations, as well as the type of ecosystem required to meet all environmental conditions needed for the survival of the organism, species, population or community
Ecosystems
An ecosystem refers to a community of living organisms, along with their physical environment, interacting as a system within a specific area
This includes the living, biotic components (such as plants, animals, fungi and microorganisms) interacting with the non-living, abiotic components (such as soil, water, air, sunlight, temperature, humidity and minerals)
These abiotic components provide the essential resources and conditions necessary for the survival and functioning of the biotic community
Together, the interactions between biotic and abiotic components shape the structure and dynamics of the ecosystem, influencing factors such as biodiversity, nutrient cycling and ecosystem services
Ecosystems vary in size, from small ponds to vast forests
Each ecosystem has its own unique characteristics, shaped by factors like geography, climate and the species present within it
Ecosystems are open systems in which both energy and matter can enter and exit. For example:
Photosynthetic organisms such as plants and algae capture sunlight, which is the primary source of energy for ecosystems
Energy exits ecosystems primarily through heat released during cellular respiration, lost during trophic transfers (e.g. from herbivores to carnivores) and radiated from the Earth's surface into space
Matter can enter or exit ecosystems in the form of water, nutrients, gases or waste products produced by animals
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