Ecology: Diversity, Food Webs, Succession, and Ecosystem Dynamics

Alpha diversity

Diversity within a single site/habitat

Beta diversity

Diversity between habitats (turnover)

Gamma diversity

Total diversity for a region.

Food web

A network that maps 'who eats whom' in a community; more complex than simple food chains as they include all trophic (feeding) interactions.

Indirect interactions

Effects that occur when one species influences another through a third species, often modifying abundances in a way not directly connected by predation or competition.

Keystone predation

Occurs when a predator preferentially eats dominant competitors, reducing their abundance and maintaining species diversity.

Top-down control

Refers to higher trophic levels (predators) controlling populations of organisms lower down (e.g., herbivores).

Bottom-up control

When resource availability (nutrients, plants) sets the abundance of higher trophic levels.

Food web complexity

Complexity can be described by the number of species, trophic levels, and feeding relationships—more complex webs generally have more connections and can influence stability.

Alternative stable states

Ecosystems may exist in different states under similar environmental conditions, each with their own structure and function.

Ecological resilience

The capacity of an ecosystem to maintain its structure and function despite disturbances.

Disturbance

A relatively discrete event that disrupts community structure and changes resources or the physical environment (e.g., fire, flood).

Primary succession

Begins on a new surface without soil (e.g., after a lava flow).

Secondary succession

Starts where a community previously existed but was disturbed, leaving soil behind (e.g., after fire).

Facilitation

Early successional species modify the environment to help later species colonize.

Inhibition

Early residents hinder later arrivals.

Tolerance

Later species do not depend on or are not hindered by early arrivals, but tolerate existing conditions.

Patch dynamics

A perspective viewing ecosystems as dynamic mosaics of patches, each at various stages of development due to disturbances and succession.

Ecosystem concept

An ecosystem is the fundamental ecological unit, including organisms and their physical environment, interacting through flows of energy and cycling of matter.

Biomass

The mass of living material present.

Productivity

The rate at which that biomass is generated (new material formed per area per time).

Primary production

By autotrophs (plants, algae).

Secondary production

By consumers (animals) using energy stored by autotrophs.