Community Ecology

What are interspecific interactions and why are they important in determining the structure of ecological communities?

Interspecific interactions are relationships between individuals of different species in a community. They are important because they influence species survival, reproduction, and population sizes, shaping community structure and ecosystem balance.

Describe the plus-minus system for categorizing interspecific interactions.

The plus-minus system classifies interactions based on the effects on each species: (+) benefits, (-) harms, and (0) no effect. For example, predation (+/-), mutualism (+/+), commensalism (+/0), and competition (-/-).

What is an organism's ecological niche? How does this contrast with the organism's habitat?

An ecological niche is an organism's role in its environment, including how it uses resources and interacts with others. A habitat is simply where an organism lives. The niche describes the "job," while the habitat describes the "address."

What is interspecific competition? How is competition categorized using the plus-minus system?

Interspecific competition occurs when species compete for the same limiting resources. It is categorized as (-/-) because both species are negatively affected by reduced access to resources.

What resources do organisms in ecological communities compete for? Provide at least one example of interspecific competition.

Species compete for food, space, light, water, and nutrients. For example, plants may compete for sunlight, or lions and hyenas may compete for prey on the savanna.

Describe the concepts of competitive exclusion, resource partitioning and character displacement. Provide examples of each. What role does interspecific competition play in each of these processes?

Competitive exclusion states that two species competing for the same resources cannot coexist indefinitely (e.g., Paramecium experiments). Resource partitioning occurs when species divide resources to reduce competition (e.g., different warbler species feeding on different tree parts). Character displacement is the evolution of traits that reduce overlap (e.g., beak size differences in Galápagos finches). All result from interspecific competition.

What is predation and how does it differ from herbivory? Can herbivory be considered as a form of predation? How is predation categorized with the plus-minus system?

Predation (+/-) is an interaction where one organism (predator) kills and eats another (prey). Herbivory (+/-) involves animals eating plant parts but typically not killing the plant. Herbivory is considered a form of predation because one species benefits while the other is harmed.

Describe one or more examples of how prey species defend themselves against predators.

Prey use strategies such as camouflage, chemical defenses, mimicry, and behavioral adaptations like living in groups or fleeing. For example, skunks spray chemicals, while deer flee or hide.

Contrast cryptic coloration with aposematic coloration and indicate how both can protect organisms against predators.

Cryptic coloration (camouflage) allows prey to blend into their surroundings and avoid detection, while aposematic coloration warns predators of toxicity or danger (e.g., poison dart frogs' bright colors).

What is mimicry and how can mimicry defend an organism against predator attack? Describe two different types of mimicry involved in predator-prey relationships.

Mimicry is when one species resembles another to gain protection. Batesian mimicry occurs when a harmless species imitates a harmful one (e.g., a harmless king snake mimics a venomous coral snake). Müllerian mimicry occurs when two harmful species resemble each other, reinforcing predator avoidance.

Define parasitism, give its plus-minus outcome, and provide one or more examples of parasitism.

Parasitism (+/-) occurs when one organism (the parasite) lives on or in another (the host), deriving nourishment at the host's expense. Examples include tapeworms in animals or mistletoe on trees.

Distinguish between endoparasites and ectoparasites and provide one example of each for a specified host.

Endoparasites live inside the host's body (e.g., tapeworms in human intestines). Ectoparasites live on the host's surface (e.g., fleas on dogs).

What is symbiosis?

Symbiosis is a close and long-term biological interaction between two species, which may be mutualistic, commensal, or parasitic.

Define mutualism, give its plus-minus outcome, and provide one or more examples of mutualism.

Mutualism (+/+) benefits both species. For example, bees and flowering plants: bees gain nectar, and plants receive pollination. Another example is mycorrhizal fungi and plant roots exchanging nutrients.

Define commensalism, give its plus-minus outcome, and provide one or more examples of commensalism.

Commensalism (+/0) benefits one species without affecting the other. For example, barnacles attach to whales for transportation, while whales remain unaffected.

Why are commensal interactions difficult to document in nature?

Commensal interactions are hard to confirm because subtle positive or negative effects on either species may go unnoticed in complex natural environments.

What are primary producers? By which process do most autotrophic organisms produce biological materials?

Primary producers are autotrophs that form the base of food chains by producing organic molecules from inorganic sources. Most use photosynthesis to convert sunlight, carbon dioxide, and water into glucose and oxygen.

Explain the terms primary consumer, secondary consumer and tertiary consumer.

Primary consumers (herbivores) eat producers. Secondary consumers (carnivores) eat herbivores. Tertiary consumers (top predators) feed on other carnivores.

What are detritivores or decomposers? What is their function in ecological communities?

Detritivores (like earthworms) and decomposers (like fungi and bacteria) feed on dead organic matter, recycling nutrients back into the ecosystem to support producers.

Describe the pattern of energy and nutrient flow in an ecosystem.

Energy flows one-way through an ecosystem—from the sun to producers to consumers—and is lost as heat. Nutrients, however, are recycled through decomposition and nutrient uptake by plants.

Describe examples of terrestrial and marine food chains.

Terrestrial: grass → grasshopper → frog → snake → hawk. Marine: phytoplankton → zooplankton → small fish → large fish → shark.

What is a food web? How do food chains and food webs differ? What do arrows represent in food chain or food web?

A food web is a complex network of interconnected food chains showing all feeding relationships in an ecosystem. Arrows represent the direction of energy flow—from the organism being eaten to the one that eats it.

What is trophic efficiency? Why is the transfer of energy from one trophic level to the next inefficient?

Trophic efficiency is the percentage of energy transferred from one trophic level to the next, typically around 10%. Most energy is lost as heat, waste, or used for metabolism.

Why would a tertiary-consumer organism be more vulnerable to extinction than a primary-consumer organism?

Tertiary consumers occupy higher trophic levels with less available energy and smaller populations. Their survival depends on the abundance of lower-level organisms, making them more vulnerable to food web disruptions and habitat loss.