In details

Ecological succession


Orderly process of setting up and developing a community. It occurs over time and ends when a stable community is established in the area.

The Succession Steps

Let's take as an example a completely uninhabited region, like a bare rock. The set of conditions for plants and animals to survive or settle in this environment are very unfavorable:

    • Direct lighting causes high temperatures;
    • The absence of soil makes it difficult to fix vegetables;
    • Rainwater does not settle and quickly evaporates.

Living beings able to settle in such an environment must be well adapted and undemanding. These are the lichens (association of cyanobacteria with fungi), which can survive only with water, light and a small amount of mineral salts. This characterizes the formation of a pioneer community or ecese. Lichens for being the first beings to settle are called "pioneer organisms." The metabolic activity of lichens is slowly changing the initial conditions of the region. Lichens produce organic acids that gradually erode the rock, forming through erosion the first layers of soil.

Layer upon layer of lichen, they form an organic carpet that enriches the soil, leaving it moist and rich in mineral salts. From then on the conditions, not so unfavorable, allow the appearance of small plants, such as bryophytes (mosses), that need a small amount of nutrients to develop and reach the reproduction stage. New and constant modifications follow one another allowing the appearance of larger plants such as ferns and shrubs. Also small animals like insects and mollusks begin to appear.

In this way, step after step, the pioneer community evolves, until the speed of the process begins to gradually decrease, reaching a point of equilibrium, in which the ecological succession reaches its maximum development compatible with the physical conditions of the place (soil, climate, etc.). .). This community is the final step in the succession process, known as the climax community. Each intermediate step between the pioneer community and the climax is called the sere.

The characteristics of a climax community

By observing the process of ecological succession we can identify a progressive increase in biodiversity and species and in total biomass. Food webs and food chains become increasingly complex and new niches are constantly forming. The stability of a climax community is largely associated with increased species variety and the complexity of eating relationships.

This is because having a complex and multidirectional food web makes it easier to circumvent the instability caused by the disappearance of a particular species. Simpler communities have fewer food choices and are therefore more unstable. It is easy to imagine this instability when we observe how an agricultural monoculture is susceptible to pest attack.

Although total biomass and biodiversity are higher in the climax community, we have some differences from primary productivity. Gross productivity (total organic matter produced) in climax communities is large and higher than in predecessor communities. However, net productivity is close to zero, since all organic matter that is produced is consumed by the community itself. This is why a climax community is stable, meaning it is no longer expanding. In pioneer communities and beings, there is a surplus of organic matter (Net Productivity) that is exactly used for the evolution of the ecological succession process.

Expected ecosystem trends throughout (primary) succession

ECOSYSTEM ATTRIBUTES

UNDER DEVELOPMENT

CLIMAX

ENVIRONMENTAL CONDITIONS

variable and unpredictable

constant or predictably variable

POPULATIONS

Population Size Determination Mechanisms

abiotic, density independent

biotic, density-dependent

Individual Size

small

big

Life cycle

short / simple

long / complex

Growth

fast, high mortality


slow, higher competitive survivability

Production

amount

quality

Fluctuations

+ pronounced

- pronounced

COMMUNITY STRUCTURE

Stratification (spatial heterogeneity)

few

lots of

Species diversity (richness)

low

high

Species diversity (equitativity)

low

high

Biochemical Diversity

low

high

Total organic matter

few

lots of

COMMUNITY ENERGY

PPB / R

>1

= 1

PPB / B

high

low

PPL

high

low

Food chain

linear (simple)

networked (complex)

NUTRIENTS

Minerals cycle

Open

closed

Inorganic Nutrients

extrabiotics

intrabiotic

Nutrient exchange between organisms and environment

quick

slow

Role of debris in nutrient regeneration

not important

important

POSSIBILITY OF EXPLORATION BY MAN

Potential production

high

low

Ability to resist exploitation

big

small

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