1	Community Ecology Interactions among species living in the same place Populations interact with one another in diverse ways. Today we consider mutual antagonism (-,-) and cooperation (+,+).
2	Reading Assignment Today’s reading is Chapter 53, pages 1214 -1220, 1227-1229 plus pages 586-588 on global change. Lab 13 on Interspecific interactions covers much of this material.
3	Species Interactions At every place there are normally many species living together (=community). What are the possible effects of species on each other? The simplest categorization of effects is to consider pairs of species and to categorize effects as positive (+) or negative (-). In this lecture we consider -,- and +,+ population size effects when we compare species grown together versus alone.
4	Measuring Interactions Biologists sometimes measure the interaction between species as the effect on the population sizes of the species, but Other times the interactions are descriptions of events in which individuals of two species interact. The relation of individuals and populations is not always simple.
5	Biological Competition One operational definition of biological competition is to compare population size when grown together versus alone (on the same resource). This used in your lab. Two species are said to be competitors if both species have smaller populations (-, -) when grown together compared to when grown alone.
6	Alone versus Together
7	Husbanding of Organisms To compare species grown alone versus grown together, we have to know how to grow the species. Scientists do not know how to indefinitely culture most of the species found in nature. Some algae can be cultured in the lab and you used such species in your lab.
8	Population Size Outcomes when two species are grown together
9	Other ways to look at competition Niche overlap Niche is range of resources a species can use. Overlap of resource use and access to same resources leads to expectation that species will interfere with each others growth. The greater the overlap the more the interference.
10	Resource Space Ideas
11	Mechanisms of Competition Consumptive Preemptive Overgrowth Chemical Territorial Encounter
12	Competitive Exclusion Principle Formulated by G. F. Gause based on experiments with Paramecium and yeast, it states “It is not possible for species with the same niche to coexist”. It has primarily motivated studies looking for differences between two species that at least superficially coexist with the same way of life.
13	Mutualism Interactions between two species in which both species have larger populations when together than when alone (+, +). Some pairs of species are so dependent on one another that one or both species can not survive alone much less be grown alone.
14	Mutualism Examples Distantly Related The species involved in a mutualism may be far apart taxonomically Ants & Fungi Bees & Plants Fungi & protists Lichens, so distinct that they are given ‘species’ names
15	Rhizobium-Legume Mutualism Nitrogen used to be a limiting nutrient for plants in many terrestrial environments. Lightening is a major source of nitrogen compounds. Nitrogen fixation by bacteria is another major source of nitrogen compounds. The symbiosis between legumes and Rhizobium is a source of nitrogen for plants.
16	Mutualism Examples Closely Related Mutualisms can be between closely related species Fish-fish Insect-insect (Ants-treehoppers) Ants protect the treehoppers from predators and benefit by eating excretions of the treehoppers (Similar to human relations with domestic animals)
17	Mutualisms involving Ants Ants protect the Acacia by biting herbivores and by clearing area around tree. Tree provides a home and food for the ant. Both species benefit. Ants-treehoppers and trees. Treehoppers are herbivores that suck the sugar out of the sap but end up excreting a lot of sugar. Ants live off the excreted sugar.
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19	Ants & Treehoppers The ants population is increased by the treehoppers. Do the ants increase the treehoppers population? The ants protect the treehoppers from spider predators, but the protection is only measurable when the spiders are common. Relationships among species may be conditional on the environment.
20	Problem/Solution If species A grown alone reaches 1000 cells per ml, If species B grown alone reaches 2000 cells per ml, What would you conclude if grown together they had densities of 1000 and 2000 cells respectively? Species A utilizes only resources that can not be utilized by B, and species B utilizes only resources not useable by A (in this environment and during the time they were growing together).
21	Vocabulary Competition Niche Nice Overlap Population size Types of Interactions Competitive Exclusion Nitrogen fixation Lichen Mutualism Kinds of resources