Interactions Between Populations. Traditional approaches to population interactions have been to consider just the direct pairwise interactions This is

Interactions Between Populations


• Traditional approaches to population interactions have been to consider just the direct pairwise interactions

• This is simplistic in that the population either interact, or they do not


• There are a number of ways in which the populations my impact one another, if they do


• Competition ( - , - ) is the most widely interaction we think of

• Both parties are negatively impacted• If the resource is in short supply or high

demand, there will be competition• If that resource is prey, the form of

competition is exploitation competition


• Other kinds of competition also occur• It may be direct (agonistic) encounters such as

allelopathy or territorial defense (interference)


• Predation, parasitism, and Batesian mimicry• Predation is usually killing another organism,

although can you think of exceptions?• Parasitism could be considered a form of

‘weak’ predation


• Batesian mimicry and herbivory could also be a form of ‘weak’ predation


• Mutualism, Müllerian mimicry


• Commensalism

http://www.arkive.org/media/A3/A3252431-D9DA-4680-B01C-0B0016A30FE8/Presentation.Large/photo.jpg


• Amensalism

http://upload.wikimedia.org/wikipedia/commons/5/54/Black_Walnut_middle.JPG


• The interactions among populations can become quite intricate and therefore quite fascinating

• Consider the case of hummingbirds

http://salonunidad.wordpress.com/2009/07/07/hummingbird-ii/hummingbird-main_full/


• Four nectar feeding birds, two species of mites and four species of flowers

• Three hummingbirds are the primary pollinators

• Corollas differ in length • Strong selection for a bird/ flower

relationship


• One mite lives in Panterpe and Eugenes, others are specialists

• Even though suitable ‘habitat’ is found in other flowers, they are not found there..why?

• Male mites will actively fight/kill other species of mites within the same flower


• Within this 10 species community there is (and please name them)

• exploitative competition, interference competition, facultative mutualism, parasitism, and commensalism


• Symbiosis is a term used for a general relationship in which organisms live together without harming one another

• Neutralism: who cares• Mutualism: Acacia & ants


• Ants and many species of caterpillars

http://www.alexanderwild.com/Ants/Taxonomic-List-of-Ant-Genera/Podomyrma/9308851_BJNoZ


• Mesquite and root nodules housing bacteria that fix nitrogen

• Mycorrhizae (fungal roots)


• Bioluminescent bacteria and deep sea creatures

• Photosynthetic algae


• It has been hypothesized that ‘endosymbiosis’ exists

• The certain of the cell organelles found in higher organisms, particularly chloroplasts and mitochondria, are actually the remnants of symbiotic prokaryotic organisms that have since been permanently incorporated into the eukaryotes


• Cattle egrets & oxpeckers


• Honey guides and honey badgers


• Cleaner wrasse• Saber-toothed

bleeny


• Think about the plant/pollinator relationships that exist

• Not just large animals, but many insects (e.g. euglossine bees and epiphytic orchids)

• Up to 23km• Outcrossing


• Producing nectar and pollen (and fruit) has costs

• Rewards must be sufficient to allow returns to get them to specialize on a particular species (why?)

• However, they must be small enough to the animal will travel the distance between plants


• Obligate mutualisms are much less common than facultative ones

• Figs and fig wasps (100’s)

http://www-tc.pbs.org/wnet/nature/files/usr/sandbox/htdocs/wpmu/wnet/wp-content/blogs.dir/3/files/2008/08/gal23.jpg

http://animals.howstuffworks.com/insects/insect-pictures.htm



• Termites and the protozoans they house in their intestines

• Next generation of endosymbionts are passed to one another through shared intestinal contents


• Commensalism


• What about indirect interactions• Darwin actually accounted for this• E.g. clover, bees, mice and cats



• There is the classical exploitative competition• But there is also ‘apparent’ competition

(consider


• There are also ‘food-chain mutualisms’ (aka cascading effects)

• Aquatic example: plants, minnows, and bass

• Is it ‘bottom-up’ or ‘top-down’?


• Consider three species’ populations at the same trophic level (horizontal interactions)

• P1 and P3 are mutualists because they both inhibit P2


• A four-species system that results in an indirect mutualism is termed facilitation

• Consumers indirectly interact as they eat similar, but different prey items (but the plants themselves compete)


• Conditions that can lead to CM

• There is a considerable time lag in the indirect effects of CM


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Interactions Between Populations. Traditional approaches to population interactions have been to consider just the direct pairwise interactions This is