Lesson 5 - Life History and Succession

Disturbance

• Physical or environmental event that disrupts the structure or function of an ecosystem

• Removes biomass

• Disturbance initiates succession!

• Without disturbance, communities shift to climax species!

• Fires to floods, high winds, or landslides

Dispersal (and types of Dispersal)

• The movement of individuals (or their propagules, such as seeds, spores, or larvae) away from their place of origin

• Pioneer Species

• Intermediate Species

• Climax Community Species

Pioneer Species

• Good at dispersal

• Thrive in poor/absent soils

• Help build soils

• Short lifespan

• Lots of offspring

• Rapid growth

• Not good competitors

Intermediate Species

• Moderate dispersal

• Require some soil nutrients

• Help build soils more

Climax Community Species

• Require rich soils

• Great competitors

• Slow growth

• Good competitors

• Long lifespan

• Low dispersal rates

• Not as many offspring

• Not tolerance of harsh conditions

Succession and Stages

• The process by which the community of species and habitat in an area changes over time

• The sequence of plants and animals that appear at a site after a disturbance

• Early Succession Habitat

  • Challenging physical conditions with high light and temperature, poor soil nutrients, few soil fungi, low soil moisture, but low competition

• Mid-Succession Habitat

  • Intermediate state with both physical and biotic challenges available

• Late-Succession Habitat

  • Challenging biotic conditions with intense competition for light and soil nutrients, but more tolerable physical conditions

Life-History

• The sequence of life events involving growth and reproduction—essentially, how species allocate energy and other resources to survival and reproduction

• Allocating resources is about growth OR reproduction OR defense OR maintenance

• Every individual has a limited amount of time and energy to devote to the activities that are required to stay alive and reproduce → trade off!

(Fitness) Trade-Off

• An inevitable compromise between traits that can't both be optimized

• No species or strategy is best in all situations, and advantages always come with costs.

• Traits that improve performance in one context often reduce performance in another.

• Whether a strategy is successful depends on who else is present and what strategies they are using.

• Tradeoffs can prevent any single species or strategy from dominating, allowing coexistence

• Ecological systems shaped by tradeoffs often show dynamic outcomes, not fixed winners.

• Chance plays a role

How do trade-offs allow organisms to allocate limited resources?

• Energy budget

• Energy must be allocated to different uses

• Metabolism, Growth, Movement/dispersal, Reproduction, Defense

• Investing more in one trait means investing less in another