Topic 2.1: Individuals, Populations, Communities, and Ecosystems

The Biosphere:

  • An ecological system composed of individuals, populations, communities and ecosystems. It represents the parts of the Earth where life exists.

Species:

  • A species is a group of organisms that can interbreed and produce fertile offspring. All species have a two part name: genus (first name) and species (second name).

Tools to Identify (ID) species:

  • Dichotomous Keys

  • Comparison of specimens with reference to collections by taxonomists

  • deoxyribonucleic acid (DNA) surveys

  • Apps such as PlantNet; Naturalist


IB ESS HL Concept: Classification as Evolution Relationships

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

  • A “clade” illustrates evolutionary relationships which all the members of a taxonomic group have evolved from a common ancestor.

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


Populations:

  • A group of organisms of the same species living in the same area at the same time are capable of interbreeding

  • Ex: Canis lupus, the gray wolf is present throughout most of the northern hemisphere but populations are defined by more limited geographical regions.


Communities and Habitats

  • Community → collection of interacting populations within the ecosystem

  • Habitat → location in which a community, species, populations or organisms primarily reside


Ecosystems as Open Systems

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

  • An ecosystem is a community and the physical environment in which it interacts


Abiotic and Biotic Factors determines the Distribution of the population:

  • Abiotic Factors → refers to non-living physical factors that may influence organisms

  • Biotic Factors → refer to the living components of the ecosystem (plants, animals, fungi, etc.)


Population Interactions

Populations interact in ecosystems by:

  • Herbivory

  • Predation (predator-prey interactions. Lion kills sheep)

  • Parasitism

  • Mutualism

  • Disease

  • Competition

These all have ecological, behavioral, and environmental consequences


Niches

A niche describes the particular set of abiotic and biotic conditions and resources upon which an organism depends:

  • An ecological niche is the role of a species in an ecosystem


Fundamental and Realised Niches

  • The fundamental niche describes the full range of conditions and resources in which a species could survive and reproduce.

  • The realised niche describes the actual condition in which a species exists due to biotic conditions.


Population Regulation — Carrying Capacity

  • Carrying Capacity: the average size of a population determined by competition for limited resources

  • Carrying capacity is not a fixed number. It fluctuates over time as the amount of resources available change.

  • Human activity such as deforestation, pollution, and overfishing can also significantly alter carrying capacities


Population Regulation — Density-Dependent Factors

  • Density Dependent Factors: more influential as population density increases. Examples include:

  • - Competition for resources: as a population grows, competition for limited resources like food, water, and shelter intensifies

  • Predation Risk: Dense populations become easier targets for predators. Predators are a natural check on prey populations.

  • Disease transmission: Disease spread more easily with higher population density. Outbreaks can devastate populations, bringing population size down.


Population Regulation — Independent Factors

  • Density independent factors can significantly impact population size but do not need a dense population to occur

  • Example: natural disasters, climate change, and human activity (deforestation, hurricanes)


Keystone species

  • These types of species have a significant impact on community structure.

  • Heightened risk of ecosystem collapse if they are removed

  • Example: Elephants and Savannahs: African elephants are Keystone herbivores in Savanna ecosystems. They feed on shrubs and trees, preventing them from outgrowing grasses.


IB ESS HL Concept: Life Cycles of r- and K- Strategists

r-Strategists

  • Species that produce large numbers of offspring to colonize new habitats quickly and make use of short lived resources

  • More competitive in young, changeable habitats in early parts of succession.

  • Lay many eggs, but little parental care to offspring

  • Large proportion of offspring die before reaching adulthood

K-strategists

  • Species that produces a small number of offspring, which increases their survival rate and enables them to survive in long-term climax communities.

  • Tend to give more parental care to the offspring, investing more energy into the process

  • more competitive in stable, established enviorments


* One way to remember the difference between r- and K strategists: r-Strategists tend to be smaller organisms (hence the lowercase r), and K-strategists tend to be larger animals (hence the uppercase K).


Carrying Capacity for Humans

Limiting factors on the growth of human populations have incresingly been eliminated due to the following:

  • reduced natural predation

  • technological advancements

  • broad and changing niche

  • mobile resources

  • changing consumption patterns

Some of the consequences for ecosystems include:

  • Resource depletion’

  • habitat destruction

  • pollution


IB ESS HL Concept: Human Impacts and Conservation Biology

Knowledge of species classifications, niche requirements, and life cycles help us to understand the extend of human impacts upon them

  • Species Classification: Knowing an organism’s taxonomic position allows one to understand its basic biology and potential vunerabilities.

  • Temperature changes from climate change affect the life cycles of plants, which also affects the life of animals

  • Niche requirements: each species has specific requirements for survival and reproduction. Knowing these requirements help us identify potential threats from human capacity that disrupt those needs.

  • Life Cycles: A species’ life cycle, from birth to reproduction, reveals critical stages that might be sensitive to human disturbance