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 species 4. 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 changes May have positive, negative, or neutral effects for organisms interacting Members of two or more species may compete for the same resource Limiting resource is in the shortest supply relative to demand Consumer–resource interactions: 1 organism gets nutrition from another Ex: predation, herbivory, parasitism

Intraspecific interactions (competition within species) determine density-dependent population growth INTERspecific interactions also modify per capita growth rates Ex: experiments on Paramecium

Analyze the graph to answer # 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 rate When two species coexist, they have lower carrying capacities than either would alone In some cases, competition causes one species to go extinct

Interspecific interactions can affect species distributions Competitive interactions can restrict the habitats in which species occur Ex: Barnacles

Intraspecific competition must be stronger than interspecific competition for 2 competing species to coexist Overlapping 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 individuals Natural 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 competition Ex: 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 species Ex. Monarch and Viceroy butterflies Müllerian mimicry - two or more harmful species resemble one another Ex. 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 mutualisms Ex: 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 outcompete No natural enemies Spread by humans Carried on ships “Hitchhiking” Deliberate introductions

Flowering plants can alter relationships between native plants and their pollinators Ex: purple loose strife Some cause extinctions Ex: American chestnut Species introduced to control specific pests can alter interactions of native species Ex: 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?