2.1 Individuals, populations, communities, and ecosystems

Guiding question

How can natural systems be modelled, and can these models be used to predict the effects of human disturbance?

This is my video for the first part of ESS topic 2.1. Learn how biotic and abiotic components of ecosystems influence the populations of organisms that live there. I review how density-independent and density-dependent factors, herbivory, predation, parasitism, and mutualism influence the carrying capacity of ecosystems.

Click here for a free Quizlet vocabulary set for ESS topic 2.1 Individuals to ecosystems. It includes vocabulary for SL ESS and HL ESS.

SL and HL knowledge statements

2.1.1 The biosphere is an ecological system composed of individuals, populations, communities, and ecosystems.

*Levels of Organisation in Ecology, by Projectoer, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons*

2.1.2 An individual organism is a member of a species.

2.1.3 Classification of organisms allows for efficient identification and prediction of characteristics.

2.1.4 Taxonomists use a variety of tools to identify an organism.

2.1.5 A population is a group of organisms of the same species living in the same area at the same time, and which are capable of interbreeding.

2.1.6 Factors that determine the distribution of a population can be abiotic or biotic.

2.1.7 Temperature, sunlight, pH, salinity, dissolved oxygen and soil texture are examples of many abiotic factors that affect species distributions in ecosystems.

2.1.8 A niche (a.k.a. ecological niche) describes the particular set of abiotic and biotic conditions and resources upon which an organism or a population depends.

2.1.9 Populations interact in ecosystems by herbivory, predation, parasitism, mutualism, disease and competition, with ecological, behavioural and evolutionary consequences.

Here’s a Khan Academy video summarising the major population interactions you’ll encounter in the ESS course.

2.1.10 Carrying capacity is the maximum size of a population determined by competition for limited resources.

2.1.11 Population size is regulated by density-dependent factors and negative feedback mechanisms.

2.1.12 Population growth can either be exponential or limited by carrying capacity.

2.1.13 Limiting factors on the growth of human populations have increasingly been eliminated, resulting in consequences for sustainability of ecosystems.

2.1.14 Carrying capacity cannot be easily assessed for human populations.

2.1.15 Population abundance can be estimated using random sampling, systematic sampling or transect sampling.

Six ways to measure populations of fish in freshwater ecosystems.

2.1.16 Random quadrat sampling can be used to estimate population size for non-mobile organisms.

2.1.17 Capture–mark–release–recapture and the Lincoln index can be used to estimate population size for mobile organisms.

2.1.18 A community is a collection of interacting populations within the ecosystem.

2.1.19 Habitat is the location in which a community, species, population or organism lives.

2.1.20 Ecosystems are open systems in which both energy and matter can enter and exit.

2.1.21 Sustainability is a natural property of ecosystems.

2.1.22 Human activity can lead to tipping points in ecosystem stability.

2.1.23 Keystone species have a role in the sustainability of ecosystems.

2.1.24 The planetary boundaries model indicates that changes to biosphere integrity have passed a critical threshold.

2.1.25 To avoid critical tipping points, loss of biosphere integrity needs to be reversed.

Knowledge statements for HL only

2.1.26 There are advantages of using a method of classification that illustrates evolutionary relationships in a clade.

2.1.27 There are difficulties in classifying organisms into the traditional hierarchy of taxa.

2.1.28 The niche of a species can be defined as fundamental or realised.

Here are 5 case studies that demonstrate the concepts of fundamental and realized ecological niches.

2.1.29 Life cycles vary between species in reproductive behaviour and lifespan.

2.1.30 Knowledge of species’ classifications, niche requirements and life cycles help us to understand the extent of human impacts upon them.

Practical activities

Use dichotomous keys, applications and databases for the identification of species.
Investigate a local ecosystem.
Use methods for measuring at least three abiotic factors in an aquatic or terrestrial ecosystem, including the use of data logging.
Use models that demonstrate feeding relationships, such as predator–prey.
Use quadrat sampling estimates for abundance, population density, percentage cover and percentage frequency for non-mobile organisms and measures change along a transect.
Use the Lincoln index to estimate population size and understand the assumptions made when using this method.

Possible engagement opportunities

Carry out an ecological investigation on natural and disturbed ecosystems using the application of skills explored in this subtopic. Secondary data can be used as a comparison.
Raise awareness of biodiversity loss.
Take part in citizen science projects that collect data on species distributions and abundance.

Happy learning!