Chapter 9 - From populations to community (CHAPTER)

Question 1

Abundance and Distribution

Answer 1

Determined by a combination of abiotic (conditions, resources) and biotic (competition, mutualism, predation, parasitism) factors.

Question 2

Context is key

Answer 2

Populations must be viewed within the context of the whole community and patchy environments.

Question 3

Data goes beyond numbers

Answer 3

Satisfactory studies estimate age classes, sexes, and size groups, not just total numbers.

Question 4

Correlations vs. Causation

Answer 4

Correlations with external factors (food, weather) can help predict but don’t prove causal relationships; mechanisms are needed for proof.

Question 5

Fluctuation and Stability

Answer 5

Populations can show overall stability with underlying complexity (irruptions, temporary trends).

Question 6

Determination of Abundance

Answer 6

Reflects all factors affecting a population, density-dependent or independent.

Question 7

Regulation of Abundance

Answer 7

Focuses on density-dependent processes (competition, predation, parasitism) that keep populations within limits.

Question 8

k-value Analysis (Key Factor Analysis)

Answer 8

Identifies key phases in a life cycle by measuring mortality (k-value) in each phase.
- Calculated from life tables.
- Helps determine factors influencing mortality fluctuations and regulation.

Question 9

Density Dependence

Answer 9

Mortality greatest when density is highest; indicates a potential role in regulation.

Question 10

Limitations of k-value Analysis

Answer 10

More complex alternatives exist.

Question 11

Migration Importance

Answer 11

Can be vital in determining and/or regulating abundance.

Question 12

Patchy Populations

Answer 12

Abundance determined by size and distance of habitable sites and species’ dispersal distance.

Question 13

Metapopulation

Answer 13

A collection of subpopulations with a realistic chance of extinction and recolonization.
- Emphasis on colonization and extinction of subpopulations, not just local birth/death.
- Can persist stably through a balance of extinctions and recolonizations of subpopulations.

Question 14

Theory of Island Biogeography (MacArthur & Wilson)

Answer 14

Introduced balance of extinction and colonization on islands.

Question 15

Levins’s Model

Answer 15

Formalized metapopulation concept with dynamics at individual and patch levels.

Question 16

Metapopulation Dynamics

Answer 16

Fraction of occupied patches (p(t)) changes based on colonization and extinction rates.

Question 17

Types of Metapopulations

Answer 17

Continuum from nearly identical subpopulations to those with some effectively stable.

Question 18

Source and Sink Networks

Answer 18

Some networks (sources) provide colonizers for others (sinks), preventing extinction.

Question 19

Transient Behaviour

Answer 19

Metapopulation dynamics can be far from equilibrium.

Question 20

Distinguishing True Metapopulations

Answer 20

Recolonization by dispersal (not just germination from seed banks) is crucial.

Question 21

Plant Metapopulations

Answer 21

Exist, and molecular methods can help track dispersal and colonization.

Question 22

Disturbances and Gaps

Answer 22

Common and lead to local extinctions, creating opportunities for colonization.

Question 23

Founder-Controlled Communities

Answer 23

All species are good colonists and equal competitors; species richness maintained by competitive lotteries.
- Priority effects can occur where the first colonizer holds the gap.

Question 24

Dominance-Controlled Communities

Answer 24

Some species are competitively superior; succession is more predictable.
- Early species are good colonizers and fast growers.
- Later species tolerate lower resources and outcompete early species.
- Succession involves an increase then decrease in species number.

Question 25

Primary Succession

Answer 25

Colonization of newly exposed substrates with no remaining seeds or spores.

Question 26

Secondary Succession

Answer 26

Re-establishment after disturbance where seeds and spores remain.

Question 27

Chronosequences

Answer 27

Spatial community gradients can represent temporal succession stages.

Question 28

Old-Field Succession

Answer 28

Succession on abandoned farmland with predictable stages. - Early succession plants (fugitives) prioritize rapid growth and dispersal. - Later succession plants are slower growing with longer lifespans and heavier seeds.

Question 29

Animal Succession Follows Plants

Answer 29

Changes in animal communities often reflect changes in plant communities.

Question 30

Climax Community

Answer 30

A relatively stable end stage of succession; may not always be reached due to further disturbances.

Question 31

Patch Dynamics

Answer 31

Succession occurs in a mosaic of patches at different stages, influenced by patch size and shape.

Question 32

Conservation and Succession

Answer 32

Maintaining specific successional stages may be crucial for endangered species.

Question 33

Complex Interactions

Answer 33

Species exist within a web of interactions (predator-prey, parasite-host, grazer-plant, competitors) across trophic levels.

Question 34

Direct vs. Indirect Effects

Answer 34

Species can affect others directly or indirectly through pathways in the food web.

Question 35

Trophic Cascade

Answer 35

A predator's effect cascades down trophic levels, e.g., predators reduce herbivores, increasing plants. - Can occur across multiple trophic levels. - Strength can depend on food web complexity and nutrient availability.

Question 36

Top-Down Control

Answer 36

Higher trophic levels control lower levels (e.g., predators controlling herbivores).

Question 37

Bottom-Up Control

Answer 37

Lower trophic levels influence higher levels (e.g., resources limiting consumers).

Question 38

Combination of Controls

Answer 38

Top-down and bottom-up effects often interact.

Question 39

"Why is the World Green?" Debate

Answer 39

Top-down view: Predators keep herbivores in check, allowing plants to accumulate biomass. Bottom-up view: Plant defenses and limited palatable resources also restrict herbivore populations.

Question 40

Meta-Analyses

Answer 40

Suggest predator manipulation has a significant negative effect on herbivores and a positive trophic cascade on plants. Fertilization shows bottom-up effects but less consistently across trophic levels.

Question 41

Stability Definitions

Answer 41

4 - Resilience - Resistance - Fragile stability - Robust stability

Question 42

Resilience

Answer 42

Speed of return to former state after disturbance.

Question 43

Resistance

Answer 43

Ability to withstand change in the face of disturbance.

Question 44

Fragile Stability

Answer 44

Stable to small disturbances, unstable to large ones.

Question 45

Robust Stability

Answer 45

Remains roughly the same despite large disturbances.

Question 46

Keystone Species

Answer 46

Impact on community composition is disproportionately large relative to its abundance; removal leads to significant changes.

Question 47

Complexity-Stability Debate

Answer 47

Historically thought increased complexity leads to increased stability. Mathematical models often suggest increased complexity decreases the resilience of individual populations. Models suggest increased complexity (especially richness) can increase the stability of aggregate community properties (biomass, productivity) due to statistical averaging.

Question 48

Compartmentalization

Answer 48

Tendency for subsets of species to interact more strongly within themselves than with other species. - More compartmentalized food webs may be more resilient to perturbation. - Compartmentalization can arise from habitat differences, morphological constraints, and trophic level similarities.

Question 49

Empirical Evidence

Answer 49

Population stability may weakly decrease with richness. Aggregate community stability (biomass, respiration) often increases with richness. Community composition may be a better predictor of stability than overall richness.

Question 50

Environment and Stability

Answer 50

Dynamically fragile complex communities may persist in stable environments, while robust simple communities are favoured in variable environments.

Question 51

Human Perturbations

Answer 51

May have the most profound effects on dynamically fragile, complex communities in stable environments.