1.1 Introduction to Ecosystems

Introduction to Ecosystems

• An ecosystem is a community of living organisms (biotic) in conjunction with the non-living (abiotic) components of their environment, interacting as a system

• “Ecosystems are the results of biotic and abiotic interactions

Biotic and Abiotic Components of Ecosystems

• Living (biotic) things, such as

  • Producers (plants, algae, phytoplankton)

  • Herbivores

  • Carnivores

  • Omnivores

  • Detritivores

  • Soil

• Abiotic factors, such as

  • Sunlight

  • Temperature

  • Precipitation

  • Moisture/water

  • pH

  • Soil

The Big Picture

• Interactions in ecosystems can include…

  • Predator-prey relationships

  • Symbiotic interactions, such as

    • Mutualism

    • Commensalism

    • Parasitism

  • Competition

  • Within one or between multiple species

Predator-Prey Relationships

• Predators hunt and kill prey

• Biotic interaction

• For predators, prey is a food resource

• As the availability of the prey fluctuates, so does the number of predators

Symbiosis

• A close, long-term interaction between two species in an ecosystem

  • From the Greek work “sym” meaning together, and “bio” meaning living; so, symbiosis is “living together:

• Ecosystems are a result of biotic and abiotic interactions

• Ex. Mutualism, Commensalism, Parasitism

Mutualism

• Mutualism is a symbiotic relationship between two species where both receive a benefit that results in an increased chance of survival and reproduciton

• Mutualistic relationships are long-term, and both species have evolved traits over many generations that aid the relationship

• Some examples of mutualism include

  • Ants and acacia trees

  • Lichens

  • Corals

  • Clownfish and sea anemones

Commensalism

• Commensalism refers to species interactions in which one species receives a benefit, and the other species is unaffected by the interaction

• From the Latin “com” meaning same, and “mensal” meaning table; so, commensalism is “at the same table”

• Just like mutualistic relationships, commensalistic relationships are long-term, and the species involved have evolved these relationships many generations

• Some examples of commensalism include…

  • Black-backed jackals scavenging kills

  • Owls nesting in the hollows of trees

  • Cattle and egrets

  • Hermit crabs and discarded snail shells

Parasitism

• Parasitism is a relationship where on organism lives on or inside of another. The other organism is called the host. The parasitism receives a benefit (ex. food/shelter, etc.) from the host, but the host is harmed by the relationship

• While parasites do harm their hosts, they rarely cause the death of the host. This distinguishes parasitism from predation (predators hunt and kill their prey)

• Some examples of parasitism include…

  • Fleas and ticks on mammals

  • Intestinal tapeworms

  • Mosquitoes biting warm-blooded animals

  • Malarial infections in humans

Competition

• Competition results when individuals from different species or within the same species struggle to obtain the same limiting resource

• A limiting resource is any resource, biotic or abiotic, that constrains a population’s size or could potentially stop a population from growing

  • Territory or water are good examples

Competiition Between Species

• Competition between different species, sometimes called interspecific competition, occurs when the species must fight over a shared, limiting resource

• The resource might be biotic, such as access to a food source, or abiotic, such as competition for available sunlight on a forest floor

• Competition between two species is harmful for both, and overtime, species will seek to limit their use of a shared resource over which they must compete

• Resource partitioning occurs when species use limiting resources in different ways, places, or at different times, in an attempt to reduce competition

Competition within a Single Species

• Competition within a single species, sometimes called intraspecific competition, occurs when individuals must fight for the same resource that all members of a species need to survive

• As with competition between different species, these resources may be biotic, such as access to mates, or abiotic, such as space for a plant’s root systems to spread out

• In this type of competition, the “fittest” individual will gain access to the resource, and will survive to reproduce. So, intraspecific competition makes a species stronger and better adapted to its environment overall