Community Ecology Succesion

There is a general increase in community diversity (number of different species present).

As succession proceeds, the number of species in a community increases. This rise in biodiversity occurs because new habitats and niches are created over time, supporting a greater variety of organisms.

There is a general increase in the abundance of organisms (more individuals from each species).

As communities mature, resources such as soil nutrients, light availability, and shelter stabilize, allowing populations to grow larger and making the community more productive overall.

There is a general change from r-selected species to K-selected species (increased size and longevity, decreased birth and growth rates).

Early in succession, r-selected species dominate due to their rapid growth and reproduction in disturbed environments. Over time, they are replaced by K-selected species, which grow slower, live longer, and compete better for limited resources.

Compare and contrast primary and secondary succession. Specifically, identify the similarities between the two processes, the conditions that exist at the beginning of each type of succession, the potential sources of new species in each and the time frame over which each type of succession occurs.

Both primary and secondary succession involve a gradual process of ecological recovery and species replacement. Primary succession begins on bare surfaces (like lava or rock) with no soil or life, and pioneer species like lichens form soil over long timescales (hundreds to thousands of years). Secondary succession begins after a disturbance (like fire or logging) where soil remains, allowing faster recolonization (decades). Both lead to stable climax communities.

Describe four or five principal methods by which lichens alter a bare rock environment to make it more hospitable for other plant species.

Lichens break down rock through chemical weathering by secreting acids, trap dust and organic matter to form soil, add nutrients when they die and decompose, retain moisture, and stabilize the surface—creating conditions suitable for mosses and small plants.

Explain why these pioneer species are replaced by other species during succession.

Pioneer species modify the environment—adding organic matter, increasing shade, and changing moisture levels—making it less suitable for themselves but more favorable for other, competitively stronger species that replace them.

Describe the process of primary succession on glacial moraines from recently exposed bare rock to climax community. Be sure to discuss the environmental changes that occur as one dominant species gives way to another.

After glacial retreat exposes bare rock, lichens and mosses colonize first, beginning soil formation. As soil depth and nutrients increase, grasses and shrubs take hold, followed by trees like spruce and alder. Over time, a stable forest community develops. Each stage changes the soil, moisture, and light conditions, enabling the next group of species to dominate.

Explain why the climax community in the flat area is a sphagnum bog while the climax community on the slope is a forest.

Flat areas retain water and have poor drainage, leading to acidic, low-oxygen conditions where sphagnum moss thrives, forming bogs. Sloped areas drain better, allowing trees to establish, leading to a forest climax community.