1. What is a community?2. What factors will be the most significant in determining

the structure of a community?3. What is the difference between interspecific interactions

and intraspecific interactions?4. How do interspecific interactions influence fitness?

1. Many species living closely together, so that they interact with each other.

2. Interactions between organisms!3. Interspecific: organisms of difference species

Intraspecific: organisms of the same species4. Affect population densities, species distribution, and

evolution of adaptations.

Interspecific interactions (between individuals of different species) affect population densities, species distributions, and ultimately lead to evolutionary changesMay have positive, negative, or neutral effects for

organisms interactingMembers of two or more species may compete for

the same resourceLimiting resource is in the shortest supply

relative to demandConsumer–resource interactions: 1 organism

gets nutrition from anotherEx: predation, herbivory, parasitism

Intraspecific interactions (competition within species) determine density-dependent population growth

INTERspecific interactions also modify per capita growth ratesEx: experiments on Paramecium

Analyze the graph to answer #1-2.1.How does interspecific competition affect growth rate?2.How does interspecific competition affect carrying capacity?

3. What do we see happening to the P. caudatum population when it must compete with P. Aurelia?

Conclusions of experiments:Presence of a competitor always reduces

population growth rateWhen two species coexist, they have lower

carrying capacities than either would aloneIn some cases, competition causes one

species to go extinct

Interspecific interactions can affect species distributions Competitive interactions can restrict the

habitats in which species occurEx: Barnacles

Intraspecific competition must be stronger than interspecific competition for 2 competing species to coexistOverlapping niches may result from resource

partitioning—different ways of using a resource

Rarity advantage: species has a growth advantage when it is at a low density and its competitor is at a high density prevents extinction

May be harder to find predators look for other prey

May invest in more defenses—low density means more resources per capita

Other limiting factors may limit predator population growth

Describe the effect of the symbiotic interactions below on the two organisms involved as positive, negative, or neutral.1.A hyena and a lion compete for the same prey. (competition)2.Lynx hunt and eat hares. (consumer-resource)3.Bees pollinate flowers when they eat their nectar. (mutualism)4.Hermit crabs live in shells abandoned by snails. (commensalism)5.Buffalo trample ants as they walk on grass. (amensalism)

Species interactions can affect individual fitness – adaptations that gain the most from a positive interaction or suffer least from a negative interaction will increase in frequency natural selection!Intraspecific competition – traits vary among

individualsNatural selection will favor a trait and its

frequency will increase in the population (directional selection)Ex: finch beak sizes

Interspecific competition – variation in traits can affect sensitivity to interspecific competitionEx: finch vs. bee

Directional Selection: A trait or a certain variation of that trait will increase or decrease in frequency if it increases fitness. For example, if a small beak (the phenotypic trait) provides a fitness advantage due to the types of seeds available, the mean beak size over time will become smaller.

Conclusion: no island in the Galapagos supports more than one finch species with a given beak size. Beak size reveals highest fitness in response to the type of seed (food) available.

Investigation: Interspecific competition

How does the presence of bees affect mean finch size?

Small finches must compete with bees for nectar. When bees and finches coexist on an island, mean finch size is larger.

Consumer–resource interactions – the opposing interests of the consumer and the resource species can lead to an “evolutionary arms race”—prey continually evolve better defenses and predators continually evolve better offenses (coevolution)What are some examples of offenses and defenses

in plants and animals?

What defenses do we see in these organisms?

Camouflage Mimicry

Batesian

Müllerian

Batesian mimicry - harmless species resembles harmful or distasteful speciesEx. Monarch and Viceroy butterflies

Müllerian mimicry - two or more harmful species resemble one anotherEx. Yellow jacket and Cuckoo bee

Where is the Moth?

Camouflage

Mutualisms – species benefit other species because acting in their own self-interest happens to benefit others

What are some examples of mutualistic relationships?

Fitness effect of the mutualism can vary depending on environmental conditions

Ex: Mycorrhizae – fungi living on roots of plants benefit plants in nutrient-poor soils, but

can be a liability in nutrient-rich soils

Relationships between species do not always fit perfectly into these categories

Ex: clown fish & sea anemone

Cheating is common in mutualismsEx: flowers mimic

the form and smell of female insects

Ex: bees bite holes in the base of flowers and eat the nectar without pollinating

4. What is an invasive species? List some defining characteristics that classify a species as invasive.

5. List any examples of invasive species of which you are aware.

Invasive species—reproduce rapidly and have negative impacts on native species they outcompeteNo natural enemiesSpread by humans

Carried on ships“Hitchhiking”Deliberate introductions

Flowering plants can alter relationships between native plants and their pollinatorsEx: purple loose strife

Some cause extinctionsEx: American

chestnutSpecies introduced to

control specific pests can alter interactions of native speciesEx: weevils

1. Mycorrhizae are a symbiosis consisting of a fungus growing on plant roots. The fungus provides nutrients for the plant, while the plant provides carbohydrates for the fungus. Explain why this relationship may not always be beneficial to the plant. Under what conditions is the relationship mutualistic? Under what conditions is it a consumer-resource interaction that harms the plant?