Competition Limited resources
Competition Objectives:
- List positive, negative, and neutral forms of community interactions.
- Describe competition, including examples of intraspecific and interspecific competition.
- Explain how competition is potentially costly to the participants, including ways to minimize competition.
This video shows a pair of our clownfish eating small frozen shrimp. Feeding interactions are often the easiest to see: they are dramatic and make for good video. However, there are many other interactions that can occur that are more subtle. For example, the clownfish have a relationship with that large cleaner shrimp in the background. More on that relationship later on in this guide.
There are many types of interactions between species within a community. The impacts on individual organisms can be positive (+), negative (-), or neutral (0).
Community Interactions
Predation (+ -)
(positive, negative) One organism kills and eats another. Clearly one organism benefits (+) and the other is harrned (-). Example: a roadrunner bird catches and eats a lizard.
Herbivory (+ -)
(positive, negative) An herbivore eats a producer. Example: a deer eats grass and a variety of other plants.
Parasitism (+ -)
(positive, negative) An organism eats, but typically does not kill, another organism. Example: wasps lay their eggs in oak leaves and the larvae eat the leaves.
Competition (- -)
(negative, negative) . Organisms compete for the same limited resource. Example: a squirrel eats food out a bird feeder.
Mutualism (+ +)
(positive, positive) Both organisms benefit from the interaction. Example: an oxpecker bird catches and eats parasites that are on zebras.
Commensalism (+ 0)
(positive, neutral) One organism benefits, the other is not impacted. Example: an oak tree can provide shade to berry shrubs. The berries benefit from the protection, the oak tree is not impacted.
On the barnacle rocks we saw earlier this term, many different interactions are occurring simultaneously: barnacles competing for space, sea stars eating clams, snails grazing n algae.
A closer view of a world of interactions.
We will go into more depth on interactions throughout this guide, starting with competition.
Competition (- -)
Competition occurs when organisms are trying to utilize the same limited resources.
Intraspecific Competition
Competition within a species: these zebra all need water from the watering hole.
Interspecific Competition
Competition between different species. Both the bee and the butterfly need nectar.
One of the mysteries of North American mammals is why the Canada Lynx does not overlap in territory more with the similar North American Bobcat.
Competitive exclusion may be the answer; find out more in the Competition video.
You may be wondering how two species can “share” or split the same niche. Sometimes there can be subtle differences in biotic and abiotic factors that enable a partitioning of the same location. Using barnacles as an example, two different size species adhered next to each other on a rock may filter different sized food out of the water. Predators may primarily attack one species , while the other may be dealing with parasites. One species may reproduce faster, but also be more likely to get ripped off the rock in a storm. A variety of factors may be reducing direct competition between the two species.
If one species takes over the niche, like the barnacle species taking over the submerged lower parts of rocks and poles (in the video), it is no longer niche splitting, one species has competitively excluded the other. It has out-competed the other species in some manner. At its extreme, this can completely drive the out-competed species out of a habitat or even to extinction.
Bird feeders are an ideal location for studying competition. Over time bird species have evolved in ways that reduce competition, like spacing at a food source (seen here) or different species nesting at different heights on the same tree, resulting in niche splitting.
In addition to the birds seen in the video, you can hear Canada geese and crows in the background.
This year our pair of crows had multiple offspring survive which may set up intraspecific competition. If food becomes limited, the crows will start to move in a wider area and space themselves while feeding. They will stay in visual or hearing range and condense into a small group again, if threatened.
Strategies to reduce competition are important. Why would it potentially be important to reduce competition?
Answer: competition is potentially expensive in energy, injury, or lost time on other tasks. Reducing competitive encounters in the long-term may actually improve fitness (survival and reproduction).
Some species are more competitive when they reach a certain minimal population size.
These Plecostomous fish are young and small, but their large number enables them to compete for algae-covered rocks.
These crickets and sowbugs are competing for the same food. Is this intraspecific or interspecfic competition?
Despite the large number of sowbugs, the cricket population is growing fast in this terrarium. Can you see why in this video?
answers: interspecific; crickets are able to keep the sowbugs back and are getting more food.
Non-native animals may enter a habitat with a competitive advantage. The absence of predators or parasites that would have controlled their numbers in their original location may be absent. They may also be a different size or have different behaviors than endemic (native) species.
These invasive Himalayan blackberries are out-competing native shrubs.
The next section examines predation and herbivory; one organism harming another.
Check your knowledge. Can you:
- List positive, negative, and neutral forms of community interactions?
- Describe competition, including examples of intraspecific and interspecific competition?
- Explain how competition is potentially costly to the participants, including ways to minimize competition?
Go back to the Communities Guide Overview
Go forward to the Predation & Herbivory Page
Communities Lecture Guide Contents
This guide and lecture material are assessed on the weekly quiz.
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