Q2: Ecological succession Flashcards
What is meant by the phrase ecological succession?
Change in the species structure of an ecological community over time, often following disturbance
How did Clements and Gleason’s theories of succession differ from each other?
Clements: succession is predictable, deterministic, converges on stable climax community, with integrated sets of species that ‘pave the way’ for others
Gleason: species distributions respond individualistically to outside factors
How did the concept of ecological succession develop? In other words, what patterns in nature motivated this concept?
Don’t know.
What are the three models of succession proposed by Connell and Slayter?
Facilitation, tolerance and inhibition.
What is the facilitation model?
Based on the assumption that only particular species with qualities ideal for “early succession” can colonize the newly exposed landforms after an ecological disturbance.
These “colonizing” qualities include: highly effective methods of dispersal, the ability to remain dormant for long periods of time, and a rapid growth rate. However, the pioneer species are often subsequently less successful once an area has been heavily populated by surrounding species due to increased shade, litter or concentrated roots in the soil, etc.
Thus, the presence of early successional species often changes the environment so that the habitat is less hospitable for the original species’ own ecological demands and facilitates the invasion of later-successional species.
What is the tolerance model?
New pioneer species neither inhibit nor facilitate the growth and success of other species. The sequences of succession are thus entirely dependent on life-history characteristics such as the specific amount of energy a species allocates to growth.[3]
The climax community is composed of the most “tolerant” species that can co-exist with other species in a more densely populated area. Eventually, dominant species replace or reduce pioneer species abundance through competition
What is the inhibition model?
Earlier successional species actually inhibit growth of later successional species and reduce growth of colonizing species already present
Example: Pioneer species might modify the environment through rapid growth and make the area increasingly shady (essentially increasing competition for light).[3]
The environment is thus less hospitable to other potential colonizing species
The only possibility for new growth/colonization in this successional sequence arises when a disturbance leads to dominating species being destroyed, damaged, or removed. This frees up resources and allows for the invasion of other species that were not previously present.
What is ecological facilitation?
Ecological facilitation or probiosis describes species interactions that benefit at least one of the participants and cause harm to neither.
What are some effects of facilitation on multispecies assemblages?
Refuge from physical stress - individual species shelters another from physical disturbance, can also be community wide
Refuge from predation - e.g. herbivory of palatable species is reduced when they occur with unpalatable species
Refuge from competition - The crab-coral interaction described above is also an example of refuge from competition, since the herbivory of crabs on seaweed reduces competition between coral and seaweed
Improved resource availability - eg coral/zoox symbiosis
Transport - e.g. pollinators
How does facilitation affect community structure?
Many facilitative interactions directly affect the distribution of species. Facilitation most often affects distribution by simply making it possible for a species to occur in a site where some environmental stress would otherwise prohibit growth of that species.
This is apparent in whole-community facilitation by a foundation species, such as sediment stabilization in cobble beach plant communities by smooth cordgrass
How does facilitation affect diversity?
Facilitation affects community diversity (defined in this context as the number of species in the community) by altering competitive interactions.
For example, intertidal mussels increase total community species diversity by displacing competitive large sessile species such as seaweed and barnacles.[4] Although the mussels decrease diversity of primary space holders (i.e., large sessile species), a larger number of invertebrate species are associated with mussel beds than with other primary space holders, so total species diversity is higher when mussels are present.[4]
The effect of facilitation on diversity could also be reversed, if the facilitation creates a competitive dominance that excludes more species than it permits
How does facilitation affect invasability?
Facilitation of non-native species, either by native species or other non-native species, may increase the invasibility of a community, or the ease with which non-native species become established in a community.
Give an example of the facilitation model of succession.
Adjacent pioneer plants colonize the otherwise moving sands and alter the environmental constraints of the sandy environment to better suit other plant species, which can then allow for soil binding to take place.
Give an example of a tolerance model of succession
A characteristic that is often associated with the tolerance model and well documented in forest succession is survival in conditions of shade. As an uninhabited area becomes populated by different plant species, shade increases – which makes less light available for the next generation. Species that are better adapted to shady conditions will then become dominant. All of the early species inhabiting the terrain have modified the environment in a way that favors a specific k-selected characteristic
Give an example of an inhibition model of succession
In areas where bryozoans are established first, tunicates and sponges cannot grow.
