Week 2 Monday: Interaction Webs in Ecosystems

Fundamental niche

The full range of environmental conditions and resources a species can occupy

Realized niche

The restricted area or role a species actually occupies due to pressures like competition or predation

What does increasing a landscape’s heterogeneity do?

Increases niches, species diversity, and stimulates species interactions. You could increase heterogeneity by increasing plant cover, for example

Obligate mutualism

Permanent dependency where at least one of the organisms cannot survive or reproduce without the other

Protocooperation or facultative mutualism

Two different species benefit from each other, but the relationship is not necessarily for their survival

Bottom up organization by richness on lower levels results in…?

Higher diversity on lower trophic levels results in more diverse upper levels

Top down effects on lower levels

Happens when higher-level predators or consumers control the population, biomass, and structure of lower trophic levels in a food web. Includes both direct AND indirect interactions

Ex: presence of larger predators reduces large herbivores, thereby increasing plant diversity (indirect). Or, an herbivore eats a plant (direct)

Trophic cascade

A linear chain reaction where a change at one trophic level (usually a top predator) ripples down or up through at least three feeding levels

Classic Example: The reintroduction of wolves in Yellowstone National Park reduced elk numbers and changed their foraging behavior, which allowed aspen and willow trees to recover.

Node in species interaction web

Individual species in a web

Edge in species interaction web

Trophic connection between species

Food web topology

Overall structure of nodes and edges in the web

Exploitative competition

Species interact by sharing the same food source

Feedback loop

A circular, self-regulating or self-reinforcing pathway where the output of a system cycles back to influence its own input (can be negative or positive)

• Negative Feedback (Stabilizing) Example: When prey populations spike, predator numbers rise because of more food; the higher number of predators then drives the prey population back down.

• Positive Feedback (Amplifying/Destabilizing) Example: eutrophication, where excess nutrient runoff causes algae to bloom, die, and decompose, stripping oxygen and killing more life, which fuels further decay.

The Input: The variable, resource, or trigger that enters the system and drives its current action.

The Output: The final result, effect, or response that comes out of the process.

Intra guild predation

Predators eating each other

Apparent competition

An indirect negative interaction between two different species that share a common predator, parasite, or herbivore

ex:

1. Prey A increases: The population of Prey A grows.

2. Predator thrives: Because more food (Prey A) is available, the shared predator population increases or becomes better fed.

3. Prey B suffers: The higher number of predators increases the predation rate on both species.

Trophic redundancy

When multiple species share the same niche/ecological function

Ecosystem insurance

If one species goes extinct or declines, another steps in to fulfill its role

Stability

An ecosystem's capacity to maintain its equilibrium state over time

Secondary extinction

Loss of one node in the web creates extinction web in other nodes

Trait-mediated interaction

A trait in one species drives community composition in other trophic levels.

For example, herbivores begin avoiding predators in open spaces, allowing plants in those spaces to grow

Density-mediated interaction

Abundance in one species drives community composition in other trophic levels.

For example, many predators may eat herbivores, allowing plants to flourish

Resistance

The ability of an ecosystem to withstand or remain unchanged when subjected to a disturbance

Resilience

An ecosystem's capacity to recover from disturbances (or reorganize while maintaining core functions) and return to its pre-disturbed state

Tipping points

The point at which an ecosystem permanently changes into a new stable state

Community assembly

The processes that decide which groups of species arrive, establish, interact, and persist in a specific area over time

Example in a sentence: “"Researchers studied how community assembly shapes plant diversity after a wildfire clears a forest."“

Historical contingency

The idea that ecological outcomes depend heavily on the random, unpredictable sequence of past events

For example, which species colonized the area first can determine future community composition

Priority effects

When the order in which species arrive at a location determines how an ecological community grows and changes over time

Niche preemption

An ecological process where the first species to arrive in a habitat takes up available space and food, leaving fewer resources for later-arriving species

Normally effects species with similar identities

Niche modification

Species that arrive early can change the types of niches available in the site. Normally effects across guilds or functional groups

Functional group

A functional group in ecology is a set of species that share a similar ecological role or effect on an ecosystem

Guild

A specific type of functional group where species exploit the exact same resources in a similar way

Legacy effects

Past events that have altered soil structure, microbial populations, or vegetation patterns; this also means that the starting point of a community drastically affects its future

Alpha diversity

Local, within a single habitat patch.

Beta diversity

Differentiation / turnover between distinct habitats or ecosystems.

Gamma diversity

Total regional diversity across an entire landscape.