Ecosystem Heterogeneity

Ecosysgem heterogeneity

The differentiation in structure or process over 3-dimensional space or over time in any system

Examples of heterogeneity

Boreal forest fire mosaics

Plant neighborhoods

Pit and mound microtophography

Stream patchiness

Marine benthos

Spatial heterogeneity

Patch dynamics is the spatial patterning at a variety of scales and levels

Can be ephemeral, change as patches change and inter patch dynamics change

Temporal heterogeneity

Causes vary - could be disturbances, nutrient availability, animal activity, etc.

Spatial and temporal heterogeneity an be…

Hard to separate

Past human activities can influence…

An ecosystem’s metabolism

Diversity

Species distributions

Can be mitigated by negating stressors

Internal heterogeneity

Spatial pattern inside the boundaries of the ecosystem

Examples of internal heterogeneity

Pits/mounds within a forest stand or the spatial arrangement of cut versus intact forest in a small watershed

Depths of moss cover in the arctic influenced soil temps and microbial activity

Reforested riparian areas influence water temp and primary productivity

External heterogeneity

Spatial pattern outside the boundaries of the ecosystem

External heterogeneity examples

Water flows in unmanaged versus managed forested ecosystems

Mass movement of biota or other materials

Boundary effects

Those that are structurally or compositionally different are important

May act as barriers, habitat zones, or areas of interaction between patches

Ex. waterfalls, vegetation barriers, edge

Measures of heterogeneity

Qualitative / quantitative differences

• richness of entities

• frequency of entities in a landscape

• Spatial / temporal configuration

Ecosystem stability

The ability of an ecosystem to maintain its structure and function over long periods of time

Ball and cup

Resistance

Ability to withstand disturbance without altering ecosystem structure

Resilience

Ability to recover ecosystem structure change following disturbance

More biodiversity =

Great ecosystem stability

Increased diversity can lead to…

Increased ability to resist and/or recover from disturbance

Perturbation

An event or process that alters the structure or function of an ecosystem

Types of perturbation

Disturbance

Stress

Disturbance

Alter 3-dimensionally the structure of an ecosystem

Examples: fires, pest outbreak, flooding

Stress

Directly affects the metabolism or function

Examples: disease, turbidity

Pulse

Sudden (instantaneous)

Ends shortly

May repeat, if so, cyclical or irregular or not

Press

Generally long-lasting once triggered

Cannot be avoided unless organisms can go dormant or migrate

Examples: drought, winters

Alternative stable states

When a community is disturbed that has new structure and function

Two regimes (cups) that ecosystem gradient (ball) can fall into, with a critical threshold