Course: plants and environment
Chapter I: Biocenosis
Chapter Objectives
At the end of this chapter, the student will be able to: Define biocenosis and understand its role in an ecosystem. Identify the main characteristics of biocenoses. Differentiate the types of biocenoses according to various criteria.
- 1. Introduction The study of the relationships between plants and their environment relies on understanding ecosystems, which are composed of two major elements: The biotope: the set of physicochemical conditions of an environment. The biocenosis: the community of living beings (plants, animals, microorganisms) that interact within this environment. Biocenosis plays a fundamental role in ecological balance by regulating the flow of energy and nutrients through the different trophic levels (producers, consumers, decomposers).
-2. Notions of Biocenosis Definition of Biocenosis Biocenosis refers to the set of living organisms coexisting in the same environment and interacting with each other and their surroundings. This concept was introduced by Karl Möbius in 1877 to describe biological communities present in a given habitat. An ecosystem is therefore composed of: A biotope, which represents the physical environment. A biocenosis, which includes living beings and their interactions.
-2.1. Characteristics of Biocenoses Biocenoses are defined by several characteristics:
1. Specific Composition The diversity of species within a biocenosis is essential for its functioning. It includes: Species richness: the total number of species present. Relative abundance: the proportion of each species compared to others.
2. Trophic Organization Biocenoses are structured into food chains and trophic networks: Primary producers (plants, algae): convert solar energy into organic matter. Consumers (herbivores, carnivores, omnivores): feed on other organisms. Decomposers (bacteria, fungi): recycle organic matter into nutrients usable by plants.
3. Interactions Between Species Organisms within a biocenosis interact through several types of ecological relationships: Competition: two species use the same limited resource (e.g., competition for light among plants). Predation: one species consumes another (e.g., phytophagous insects). Mutualism: a beneficial relationship for both partners (e.g., mycorrhizae in plants). Parasitism: one organism lives at the expense of another (e.g., parasitic fungi on plants).
4. Dynamics and Evolution of Biocenoses Biocenoses are not static; they evolve through processes such as: Ecological succession: the gradual replacement of species within an ecosystem (e.g., recolonization of land after a fire). Ecological resilience: the ability of a biocenosis to recover after a disturbance (e.g., forest regeneration after a storm).
- 2.2. Types of Biocenoses Biocenoses can be classified according to several criteria:
1. Based on the Living Environment Terrestrial biocenosis: includes organisms living on land (forests, savannas, deserts). Aquatic biocenosis: includes communities living in aquatic environments (oceans, rivers, lakes).
2. Based on Biodiversity and Stability Stable biocenosis (climax): an ecosystem that has reached maturity with a stable ecological balance (e.g., ancient tropical forests). Unstable biocenosis (pioneer community): a community in formation, often after a disturbance (e.g., vegetation on a newly forming sand dune).
3. Based on Human Intervention
Natural biocenosis: develops without human intervention (e.g., primary forests).
Anthropized biocenosis: modified by human activities (e.g., agricultural fields, urban parks).
