Ecological succession

Ecological succession

Ecological succession, is the phenomenon or process by which a community progressively transforms itself until a stable community is formed. It is a fundamental concept in ecology, and refers to more or less predictable and orderly changes in the composition or structure of an ecological community...

 can be understood as a process of changing species composition within a community due to an ecological disturbance, and varies largely according to the initial disturbance prompting the succession. Joseph Connell and Ralph Slatyer

Ralph Slatyer

Ralph Owen Slatyer AC, FAA is an Australian ecologist, who was the first Chief Scientist of Australia from 1989 to 1992.He was born in Perth, Western Australia in 1929, and was educated at Perth Modern School and Wesley College, Perth, then the University of Western Australia from which he...

 further developed the understanding of successional mechanisms in their 1977 paper and proposed that there were 3 main modes of successional development. These sequences could be understood in the context of the specific life-history theories

Life history theory

Life history theory posits that the schedule and duration of key events in an organism's lifetime are shaped by natural selection to produce the largest possible number of surviving offspring...

 of the individual species within an ecological community.

The 1977 study

Connell and Slatyer chose to focus on autogenic succession

Autogenic succession

In ecology, autogenic succession is succession driven by the biotic components of an ecosystem. In contrast, allogenic succession is driven by the abiotic components of the ecosystem.- How it occurs :...

, which occurs on newly exposed landforms and is initiated by changes from within the community rather than a geophysical transformation. They targeted plant and immobile aquatic organisms that demanded the greatest surface area within an environment and could modify the physical landscape. They defined community as “the set of organisms that occur together and that significantly affect each other’s distribution and abundance.”

The Models

The key factor distinguishing the three models is how the process of succession affects the original, pioneer species (i.e. their relative success in later-successional stages).

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
  Pioneer species
  Pioneer species are species which colonize previously uncolonized land, usually leading to ecological succession. They are the first organisms to start the chain of events leading to a livable biosphere or ecosystem...
  
   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. (Note: See Ecological Facilitation
  Ecological facilitation
  Facilitation describes species interactions that benefit at least one of the participants and cause harm to neither. Facilitations can be categorized as mutualisms, in which both species benefit, or commensalisms, in which one species benefits and the other is unaffected...
  
  .)

Tolerance Model

In this case, 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.

• The climax community
  Climax community
  In ecology, a climax community, or climatic climax community, is a biological community of plants and animals which, through the process of ecological succession — the development of vegetation in an area over time — has reached a steady state. This equilibrium occurs because 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
  Competition
  Competition is a contest between individuals, groups, animals, etc. for territory, a niche, or a location of resources. It arises whenever two and only two strive for a goal which cannot be shared. Competition occurs naturally between living organisms which co-exist in the same environment. For...
  
  .

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).

• 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.

Examples of Each Model

1. Facilitation Model

Essentially, the facilitation model suggests that the presence of an initial species aids and increases the probability of the growth of a second species. For example, in “Physiological Controls Over Seedling Growth in Primary Succession on an Alaskan Floodplain,” by Lawrence R. Walker and F. Stuart Chapin, III, the presence of alder

Alder

Alder is the common name of a genus of flowering plants belonging to the birch family . The genus comprises about 30 species of monoecious trees and shrubs, few reaching large size, distributed throughout the North Temperate Zone and in the Americas along the Andes southwards to...

 plants aids the growth of willow

Willow

Willows, sallows, and osiers form the genus Salix, around 400 species of deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions of the Northern Hemisphere...

 and poplar

Poplar

Populus is a genus of 25–35 species of deciduous flowering plants in the family Salicaceae, native to most of the Northern Hemisphere. English names variously applied to different species include poplar , aspen, and cottonwood....

 seedlings in an Alaska

Alaska

Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

n floodplain.

Alder roots contain nitrogen-fixing bacteria, which greatly increase the amount of inorganic nitrogen present in soils. This increased availability of nitrogen aids the growth of both willow and poplar seedlings in areas without other competition. Eventually, however, willow and poplar grow more rapidly than alder, leading to a reduction in the abundance of the pioneer species, and eventually, spruce is becomes a later-succession species, due to its increased ability (over alder) to grow in shaded areas.

Another case of facilitation comes from the colonization of lakeshore

Shore

A shore or shoreline is the fringe of land at the edge of a large body of water, such as an ocean, sea, or lake. In Physical Oceanography a shore is the wider fringe that is geologically modified by the action of the body of water past and present, while the beach is at the edge of the shore,...

 sand dunes

Dune

In physical geography, a dune is a hill of sand built by wind. Dunes occur in different forms and sizes, formed by interaction with the wind. Most kinds of dunes are longer on the windward side where the sand is pushed up the dune and have a shorter "slip face" in the lee of the wind...

. 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. The giant saguaro cactus

Saguaro

The saguaro is a large, tree-sized cactus species in the monotypic genus Carnegiea. It is native to the Sonoran Desert in the U.S. state of Arizona, the Mexican state of Sonora, a small part of Baja California in the San Felipe Desert and an extremely small area of California, U.S...

, in this respect, can only survive in the shade of other plants (or in some cases rocks) - pioneer species facilitate their existence by providing shade. (The argument has also been made that this type of interaction is exemplary of the tolerance model; see below).

2. Tolerance Model

The tolerance model is completely dependent upon life history characteristics. Each species has an equally likely chance to establish itself in the early stages of succession and their establishment results in no environmental changes or impacts on other species. Eventually, early species, typically dominated by r-selected species, which prioritize fast rates of reproduction, are out-competed by K-selected species (species that become more dominant when there is competition for limited resources).

For example, we can examine succession in the Loess Plateau

Loess Plateau

The Loess Plateau , also known as the Huangtu Plateau, is a plateau that covers an area of some 640,000 km² in the upper and middle reaches of China's Yellow River. Loess is the name for the silty sediment that has been deposited by wind storms on the plateau over the ages...

 in China

China

Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

. In the graph on page 995 of the paper “Plant Traits and Soil Chemical Variables During a Secondary Vegetation Succession in Abandoned Fields on the Loess Plateau” by Wang (2002), we can see the initial dominance of the Artemisia scoparia

Artemisia scoparia

Artemisia scoparia is a species in the genus Artemisia, in the family Asteraceae. Its common name is Redstem Wormwood. It is an allergen.- Chemical constituents :# Capillarisin # Chlorogenic acid butyl ester# 6,7-Dimethylesculetin...

, the pioneer species. Over time, however, the Bothriochloa ischaemun becomes the dominant species and the abundance of Artemisia scoparia greatly declines. This is due to the rapid rate of reproduction of the Artemisia scoparia, resulting in the species’ early abundance, and the dominant competition from the K-selected Bothriochloa ischaemun, resulting in the species’ later abundance.

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.

3. Inhibition Model

In this model, one species inhibits the presence of another, either through direct means, such as predation (by eating the other species or attacking them), or indirect means, such as competition for resources.

Sometimes in inhibition models, the time of establishment of a species determines which species becomes dominant. This phenomenon is referred to as the priority effect

Priority effect

Priority effect is the impact that a particular species can have on ecological community development due to prior arrival at a site ....

 and suggests that the species that became established earlier are more likely to become the dominant species. One example of the inhibition model, and the priority effect, occurs in South Australia. In areas where bryozoa

Bryozoa

The Bryozoa, also known as Ectoprocta or commonly as moss animals, are a phylum of aquatic invertebrate animals. Typically about long, they are filter feeders that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia...

ns are established first, tunicates and sponges cannot grow.

The inhibition model has also been observed at work in forest ecosystems; in these systems the early arrivers hold a monopoly on the land, keeping other species out. Closed shrub canopies have been known to prevent tree growth and access to land for periods of up to 45 years – in an experimental study on inhibition it was found that areas occupied by large areas of Lantana

Lantana

Lantana is a genus of about 150 species of perennial flowering plants in the verbena family, Verbenaceae. They are native to tropical regions of the Americas and Africa but exist as an introduced species in numerous areas, especially in the Australian-Pacific region. The genus includes both...

sprawling shrubs excluded and inhibited the growth of tree species.

Works cited

• Connell, Joseph H. and Ralph O. Slatyer. “Mechanisms of succession in natural communities and their role in community stability and organization.” The American Naturalist 111 (982) (Nov. - Dec. 1977): 1119-1144.
• Moorcroft, Paul. “Terrestrial Succession.” Organismic and Evolutionary Biology 55. Maxwell Dworkin, Cambridge. 4 April 2011.
• Ricklefs, Robert E. The Economy of Nature. (New York, NY: W.H. Freeman and Co., 2008).
• “Sand Dunes.” National Biological Information Infrastructure- Home. Accessed 29 Apr. 2011. .
• Walker, Lawrence R. and F. Stuart Chapin, III. “Physiological Controls Over Seedling Growth in Primary Succession on an Alaskan Floodplain.” Ecology 67 (6) (Dec.,1986): 1508-1523.
• Walker, et al., “The Role of Life History Processes in Primary Succession on an Alaskan Floodplain,” 1243-1253.
• Wang, Guo-Hong. “Plant Traits and Soil Chemical Variables During a Secondary Vegetation Succession in Abandoned Fields on the Loess Plateau.” Acta Botanica Sinica 44 (8) (2002): 990-998.