Chapter 17 Flashcards
Succession
change in species composition of communities over time
Disturbances
abiotic events that physically injure or kills some individuals and creates oppurtunities for other individiuals to grow and reproduce
Abiotic Factors
Wave, currents, wind, water supply, chemical composition, temperature, volcanic activity
Biotic factors
Negative interactions: competition, predation, herbivory, disease, parasitism, trampling, digging
When does stress occur?
when abiotic factors reduce growth, reproduction, or survival of individuals and creates opportunities for others
Succession
The process by which species composition of a community changes over time.
Involves colonization and extinction by abiotic and biotic factors
Climax stage
a stable end point that experiences little change until an intense disturbance sends community back to an earlier stage
Primary succession
involves colonization of habitats devoid of life, potentially due to a catastrophic disturbance (such as on pumice plain at mount st. helens) or since they are newly made habitats such as volcanic rock.
Secondary succession
involves reestablishment of a community in which most, not all, of the organisms or organic constituents have been destroyed
Henry Chandler Cowles
studied successional sequence of vegetation in sand dunes on the shore of lake Michigan.
Cowles found a successional pattern by assuming plant assemblages farthest from lakes edge were oldest and ones nearest lakes are the youngest
Space for time substitution
used frequently to study communities over time scales that exceed life spans of ecologists, assumes that main factor of change is time, and unique conditions in specific locations are inconsequential
What did Clements and Gleason believe
Clements believed plant communities are like superorganisms that work together for some deterministic end and Gleason viewed individual species response to prevailing conditions as significant
Examples of how animals influence successional patterns
Eating
Dispersing
Trampling
And destroying
Facilitation model (inspired by clements)
early colonizers modify environments to benefit future species while limiting their own dominance, with the progression leading to a climax community where species no longer facilitate others and are displaced by disturbances.
Tolerance Model
earliest colonizers modify the environment neutrally, with early species reproducing and growing quickly, while later species persist through slow growth, few offspring, and long life, allowing them to tolerate stresses hindering early successional species.
Inhibition model
early successional species modify the environment to hinder later successional species by monopolizing resources, and this inhibition is broken when stress or disturbance reduces the abundance of the inhibitory species, enabling the persistence of later species through tolerance of environmental or biological stresses.
Glacial Retreat in Alaska (Cooper)
The melting glaciers initiated a prolonged sequence of community change, spanning centuries and progressing through pioneer, dryas, alder, and spruce stages, as evidenced by permanent plots tracking plant species richness and composition, with soil analysis highlighting notable increases in organic matter and soil moisture.
Facilitation and Inhibition Experiments in Alaska (Chapin)
Manipulative experiments involving spruce seeds across various successional stages revealed changing patterns of facilitative and inhibitory effects on spruce seedlings, with low germination in pioneer and dryas stages, a net positive effect in the alder stage, and predominantly negative effects in the spruce stage due to competition.
Salt Marsh Secondary Succession in New England (Mark Bertness and Scott Shumway)
The study on salt marsh secondary succession examined facilitative and inhibitory interactions, where disturbance in the form of wrack created bare patches; cordgrass inhibited distichlis in low intertidal zones, while black rush could colonize in the middle zone under specific conditions of distichlis presence or watering, with salt stress influencing the outcomes.
Sousa’s experiments in SoCal
Disturbances caused by waves and low tides initiate colonization and succession, as demonstrated by Sousa’s Southern California boulder field experiments, where algae domination, particularly Ulva lactuca and Gigartina canaliculata, indicated inhibition as the primary mechanism, with the transition to mid-successional algal species influenced by grazing crabs.
Terence Farrell study in Oregon
challenged the prevailing view by revealing context-dependent inhibition in sessile-dominated communities, where Chthamalus dalli, Balanus glandula, and three macroalgal species displayed a succession pattern, with Balanus facilitating macroalgal colonization and supporting the facilitation model.
Alternative scenarios and Stable States
Numerous experimental studies indicate that communities undergo succession driven by a combination of facilitation, inhibition, and tolerance mechanisms, with pioneer stages experiencing physical stressors and facilitative interactions being more prominent in early succession, leading to the dominance of slow-growing, long-lived species as succession progresses.
John Sutherland Study
Communities can exhibit stability, characterized by a return to the original structure and function after disturbance, with stability dependent on spatial and temporal scales; John Sutherland’s study on marine fouling communities identified alternative stable states, where sessile species like Styela and Schizoporella demonstrated stability influenced by fish predation.
Shifts caused by Human Activities
Human activities, including habitat destruction, species introductions, and overharvesting, have the potential to induce shifts in communities to alternative states, and these shifts may be irreversible (hysteresis); however, excluding ecosystem engineers in models can introduce spatial state issues, exemplified by tiles lacking a high spatial state.
