Biotic Potential, Environmental Factors, and Community Structure

Biotic Potential and Environmental Resistance

The biotic potential is the maximum reproductive capacity of a species if all individuals reproduce to their maximum and all offspring survive to reproductive age. Environmental resistance is the interaction of biotic and abiotic factors that regulate a population’s biotic potential. The equation dn/dt = rn generally shows populations affected by factors that regulate their biotic potential, preventing them from reaching their full potential. The pattern or curve indicates the evolution of a population’s size.

Community Structure and Properties

A community is a set of populations in a place at a specific time. A cline is a gradual change in a population along a geographic gradient. The biological structure of a community depends directly on its species composition. Key properties include:

  • Species richness or biodiversity: the number of species in a community.
  • Relative abundance: the proportion of each species in a community, which determines its functioning.
  • Dominance: the controlling influence of one or a few species on the community.
  • Biological diversity: an estimate of the complexity of a community based on the possible interactions between species.

The physical structure of a community depends on the distribution of species. This includes:

  • Horizontal structure: the dispersion patterns of species and their relationships.
  • Seasonality: cyclical changes in the community structure.

Primary Production and Limiting Factors

Primary production is the fixation (gross primary production) or accumulation (net primary production) of energy and nutrients by autotrophs. It is measured in energy (kcal/m2d) or quantity (g/m2d). Liebig’s law of the minimum states that an individual’s growth is limited by the essential nutrient present in the smallest amount relative to demand. Tolerance refers to the limits within which an organism can thrive. Organisms can gradually adjust to changing conditions. Stenoic species cannot tolerate large variations in a factor, while eurioic species can tolerate large variations.

Ecosystems and Ecological Concepts

An ecosystem is a biological system where organisms interact with each other and their environment. These interactions involve the transfer of matter, energy, and information. Energy is consumed and dissipated as heat. The ecosystem is a basic unit of nature. r-strategists have a high intrinsic growth rate, high migration capacity, and are adapted to unstable habitats, while k-strategists have a low growth rate and are adapted to stable habitats. The Clementsian hypothesis considers communities as superorganisms, with succession following a predictable sequence, culminating in a climax community. Environmental conditions are chemical or physical attributes that affect biological processes, while environmental factors are resources that are consumed.

Sampling and Population Estimation

The capture-recapture method estimates population size by marking and recapturing individuals. It assumes a constant population during the sampling period. The minimum area is the smallest area that contains almost all species of a community. The Lury method estimates population size based on the proportion of individuals captured. Sampling is a statistical procedure to estimate population parameters. Spatial distribution is measured using a dispersion index based on the ratio of variance to the mean: id = s^2 / x. A value of 1 indicates random distribution, less than 1 indicates uniform distribution, and greater than 1 indicates contagion.