Predicting successional changes
Changes in Species Interactions
As succession proceeds, interactions between species shift from simple to complex. Early communities have few species, so interactions are limited, often just basic competition for space and light.
As more species arrive, food webs expand, predation and mutualism become common and niches diversify. These increasing interactions strengthen stability and help regulate population sizes.
Changes in Abiotic Factors
Abiotic conditions improve as succession advances. Early stages often have poor soil, low nutrients, high light exposure and wide temperature fluctuations.
Pioneer plants modify these conditions by adding organic matter, trapping moisture and stabilising the substrate. Over time, the environment becomes more fertile and buffered, allowing larger, more competitive species to establish.
Changes in r & K-Selected species
r-selected species dominate early succession. They grow quickly, reproduce rapidly and tolerate harsh conditions. They help begin the recovery process by binding soil, providing shade and increasing organic matter. However, they are usually outcompeted as conditions improve and later species arrive.
K-selected species dominate late succession. They grow slowly, are long-lived and compete well for light, water and nutrients. They form stable, mature communities with high structural complexity. Their arrival marks the shift towards a climax community with increased stability.
Changes in biodiversity
Biodiversity is low at the start because only a few hardy pioneers can survive. As the environment improves, more species can establish, increasing richness and interactions. Late succession and climax communities have the highest diversity. This greater diversity improves resilience and supports complex food webs.
Changes in biomass
Biomass starts low because early species are small and fast-growing. It increases steadily as shrubs, young trees and eventually mature trees take over.
Climax communities contain the highest biomass due to large, long-lived species. Increased biomass boosts productivity and strengthens ecosystem stability.
| Feature | Start of succession | End of succession (climax community) |
| Type of species present | R-selected, small organisms that are fast growing | K-selected, larger organisms that are slower growing |
| Biodiversity | Low | High |
| Biomass | Low | High |
| Biotic interactions | Simple interactions based on food chains | Complex interactions based on food webs |
| Abiotic interactions | Bare ground, or poor quality soil, low nutrient levels. Unstable. | Good quality soil and high levels of nutrients. Stable. |
r-strategists typically live in unstable, unpredictable environments where the ability to reproduce rapidly (exponentially) is important.
K-strategists occupy more stable environments. They are larger in size and have longer life expectancies. They are stronger or are better protected and generally are more energy efficient.
In general, communities in early succession will be dominated by fast-growing, well-dispersed species (pioneer/r-selected life-histories).
As succession proceeds, these species will tend to be replaced by more competitive (k-selected) species. They tend to inhabit relatively stable biological communities, such as late-successional or climax forests.