APES 1.1 Introduction to Ecosystems

• Ecosystems are the result of biotic and abiotic interactions

Biotic: Organic matter, living things. EX: oysters, blue crabs, zooplankton, phytoplankton, jellyfish, kelp, grass, trees, birds, etc.

Abiotic: Climate, nonliving things. EX: Sunlight, temperature, nutrients, humidity, soil, rocks

• Biotic and abiotic components of an ecosystem provide boundaries that distinguish one ecosystem from another
• Some ecosystem boundaries are very well defined, others are not
• While it may be beneficial to divide various locations of the earth into distinct ecosystems, it is also important to remember that each ecosystem interacts and are not mutually exclusive
  • They exchange energy and matter
• As a result, changes in one ecosystem can have extensive effects on the global system and environment
• Community ecology examines species interactions within a given habitat
• There are four types of interactions between different types of species
  • Competition, predation, mutualism, commensalism

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Predation

• Predation is a positive / negative relationship between predator and prey
• The predator survives by killing and eating prey
• Predators are always in a higher trophic level than their prey

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• Predation is a type of symbiotic relationship between organisms of different species
• Predation refers to the use of one species as a resource by another species
• Predation is a natural mechanism of population control

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• There are four types of predators
  • True predators usually kill their prey and consume most of what they kill
  • Herbivores consume plants as prey. An herbivore usually only eats a portion of the individual plant without killing it
  • Parasites live on or in the organism they consume, called the ‘host.’ A parasite rarely causes the death of its host. Parasites can cause diseases in their host called pathogens. Pathogens include viruses, bacteria, fungi, protists, and worm-like helminths.
  • Parasitoids are organisms that lay their eggs inside of other organisms. When the eggs hatch the parasitoid larvae consume the host from the inside out, usually killing the host.

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• Predator-prey relationships are dynamic and provide insight into the fluctuations of species populations within an ecosystem over a given period of time
• When the predator population is lowest, prey pop. increases as there is less predation
• When the prey pop. is highest, the predator pop. increases due to increased availability of food
• Subsequently the prey pop. drops, and predator pop. drops soon after from a decrease in availability of food
• This delayed reaction relationship constantly fluctuates in this manner

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Types of Symbiosis

Mutualism: A symbiotic relationship in which both species involved benefit from the interaction by allowing for an increase in the probability of survival and/or reproduction

Commensalism: A symbiotic relationship in which one species benefits from the interaction while the other species is not affected by the interaction

Parasitism: A symbiotic relationship in which one species benefits from the interaction while the other species is harmed by the interaction

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• Competition can occur within or between species in an ecosystem where there are limited resources

Resource partitioning: Using resources in different ways, places, or at different times. This can reduce the negative impact of competition

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• Ecological competition is the interaction between organisms or species trying to utilize the same resource within the same ecosystem
• Resources limited in supply may include food, water, shelter, light, territory, nutrients, etc.
• Members within a given species may also compete for reproductive success.
• Intraspecific competition is competition between members of the same species.
• Interspecific competition is competition between individuals of different species.
• Competition can take place in both a direct and indirect manner as multiple biotic and abiotic variables may be involved.

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Competitive Exclusion: States that two species competing for the same limiting resource cannot coexist

• So, under a given set of environmental conditions, if two species have the same niche, one species will perform better and will drive the other species to a point of extinction within that niche.

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Resource partitioning

• Reduction in competition between species may be the result of temporal resource partitioning, spatial resource partitioning, and morphological resource partitioning.
• Temporal resource partitioning reduces competition by utilizing the same resource but at different times.
• Spatial resource partitioning reduces competition by utilizing different habitats.
• Morphological resource partitioning reduces competition by utilizing evolutionary differences in body shape or size.

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