Biol 1110-Community Ecology

What is a habitat?

The type of place where an organism lives, including its physical and chemical characteristics, such as climate and geography.

What are the main types of interspecific interactions, and how do they affect each species?

• Competition (−/−): both are harmed.

• Exploitation (+/−): one benefits while the other is harmed.

• Mutualism (+/+): both benefit.

• Commensalism (+/0): one benefits while the other is unaffected.

What is interspecific competition, and how can it affect evolution?

Different species compete for limited resources needed for growth and survival. Competition can drive evolutionary changes as species adapt to reduce resource overlap.

What is an ecological niche, and what is resource partitioning?

A niche is the set of abiotic and biotic resources an organism uses. Resource partitioning occurs when similar species use resources differently, reducing competition and allowing coexistence.

What is the difference between a fundamental niche and a realized niche?

Fundamental niche: the full range of conditions and resources a species could potentially use.

Realized niche: the range it actually occupies, often restricted by competition and other interactions.

What is character displacement?

Evolution of differences in morphology or resource use between competing species, reducing competition and allowing coexistence.

What is exploitation, and what are its three main forms?

A (+/−) interaction in which one organism benefits by feeding on another, which is harmed. Its main forms are predation, herbivory, and parasitism.

What is predation, and how do predator and prey adaptations evolve?

Predation occurs when one species kills and eats another (+/−). Natural selection favors predator adaptations for capturing prey and prey adaptations for avoiding capture.

What are four prey adaptations that reduce the risk of predation?

• Cryptic coloration: camouflage that hides prey.

• Aposematic coloration: bright warning colors signal danger or unpalatability.

• Batesian mimicry: a harmless species resembles a harmful or unpalatable one.

• Müllerian mimicry: multiple harmful or unpalatable species resemble one another.

What is herbivory, and how do plants defend themselves?

Herbivory occurs when an organism eats parts of a plant or alga, harming but not necessarily killing it. Plants defend themselves with chemical toxins and structural defenses such as thorns and spines.

What is parasitism, and what are its main types?

A parasite obtains nourishment from a host, harming it. Endoparasites live inside the host (tapeworms), while ectoparasites feed on its exterior (ticks and lice).

How can parasites affect host populations and behavior?

Parasites can reduce host survival, reproduction, and population density. Some alter host behavior to increase transmission to new hosts. Disease-causing bacteria, protists, and fungi can also harm hosts.

What is mutualism, and what are obligate and facultative mutualism?

Mutualism is a (+/+) interaction that increases both species' survival or reproduction.

• Obligate: at least one partner cannot survive without the other.

• Facultative: both partners can survive independently.

What are four examples of mutualism, and what is coevolution?

nitrogen-fixing bacteria in legume roots

cellulose-digesting microbes in termites

nutrient exchange between fungi and plant roots (mycorrhizae)

algae photosynthesizing in corals

Coevolution occurs when interacting species evolve related adaptations in response to one another.

What is commensalism, and what are two examples?

A (+/0) interaction in which one species benefits while the other is unaffected. Examples include barnacles attached to whales and cowbirds or cattle egrets feeding on insects flushed out by grazing herbivores.

What is facilitation, and how does it differ from symbiosis?

Facilitation occurs when one species improves another's survival or reproduction without requiring direct, intimate contact. For example, black rush can make salt-marsh soil more suitable for other plants.

What is species composition, and how do species richness and relative abundance contribute to community diversity?

Species composition describes which species are present, their relative abundances, and their feeding relationships.

Species richness is the number of species, while relative abundance is the proportion of individuals belonging to each species.

How does community diversity affect resistance to invasive species?

More diverse communities tend to be more resistant to invasion. Invasive species become established outside their natural ranges and can alter existing communities.

What is trophic structure, and how are food chains and food webs related?

Trophic structure describes feeding relationships that determine energy flow and chemical cycling. A food chain shows a sequence of feeding relationships, while a food web connects multiple food chains.

What are the main trophic levels and feeding groups in a food chain?

• Primary producers: autotrophs, such as plants.

• Primary consumers: herbivores that eat producers.

• Secondary, tertiary, and quaternary consumers: carnivores at progressively higher levels.

• Decomposers: break down dead organic matter.

• Omnivores: feed at multiple trophic levels.

Why are food chains generally short?

The energetic hypothesis states that energy transfer between trophic levels is inefficient. Too little energy remains available to support many successive consumer levels.

What are foundation species, and how can they shape communities?

Foundation species have strong community effects because of their large size/high abundance. They may modify habitats or dominate resources. For example, beavers build dams that transform forests into wetlands.

What are keystone species, and how do they differ from foundation species?

Keystone species have a disproportionately large effect on community structure relative to their abundance because of their ecological role. Foundation species generally influence communities through their large size or high abundance.

What is the difference between bottom-up and top-down control?

• Bottom-up: nutrients influence producers, which influence herbivores and then predators.

• Top-down: predators limit herbivores, which affects plant abundance and nutrient dynamics.

What is a disturbance, and what does the intermediate disturbance hypothesis predict?

A disturbance changes a community by removing organisms or altering resources. The hypothesis predicts that moderate disturbance produces greater diversity than very low or very high disturbance.

Why can both low and high disturbance reduce species diversity?

• Low disturbance: competitively dominant species may exclude weaker competitors.

• High disturbance: environmental stress or frequent disruption excludes species that cannot tolerate or recover from it.

What is the nonequilibrium model of community structure?

It describes communities as continually changing, often because disturbances prevent them from reaching a stable equilibrium in species diversity or composition.

What is ecological succession, and how do primary and secondary succession differ?

Succession is the gradual replacement of species in a community over time.

• Primary succession begins where soil has not formed.

• Secondary succession follows a disturbance where soil remains intact.

What are the main stages of primary succession?

Lichens and mosses colonize bare surfaces, often from windblown spores. They help soil develop, allowing grasses, shrubs, and eventually trees to establish. Initially, microbial life such as protists and prokaryotes may also be present.

How does secondary succession proceed, and what commonly causes it?

Herbaceous plants recolonize soil using seeds dispersed by wind or animals. Shrubs and eventually trees may replace them. Causes include fires, harvesting, logging, and other disturbances that leave soil intact.

What do early pioneers do for later arriving ones?

• Facilitate: make environment more favourable (making soil fertile)

• Inhibit: colonization by later species occurs in spite of activities of early ones 

• Tolerate: later species is completely independent of early ones 

How do human activities disturb communities and ecosystems?

Agricultural development, logging, urban clearing, mining, farming, and ocean trawling remove organisms or alter habitats and resource availability, changing community composition.

Why must pathogens find new hosts, and what roles do vectors and reservoirs play?

Pathogens need resources to reproduce, but hosts eventually die, so pathogens must reach new hosts. Vectors carry pathogens between hosts, while animal reservoirs are species in which pathogens persist and multiply, often causing little harm.

What are zoonotic pathogens, and how can they spread to humans?

Zoonotic pathogens are transmitted from other animals to humans. They may persist in animal reservoirs, such as bats or rodents, and reach humans directly or through vectors or other transmission routes.