The prevalence of pests and diseases which affect plants and animals in a terrestrial habitat is

Pests and diseases that affect plants and animals in a habitat are biotic factors. Biotic factors are the living components of an ecosystem that influence other organisms. Pests (such as insects, rodents, and parasitic organisms) and disease-causing agents (bacteria, viruses, fungi, protists) are all living organisms or products of living organisms, making their prevalence a biotic factor.

Abiotic factors are the non-living physical and chemical components of the environment, such as temperature, light, water, pH, and wind. Edaphic factors are a subset of abiotic factors relating specifically to soil properties (texture, pH, mineral content, water-holding capacity, humus content). Climatic factors are another subset of abiotic factors related to weather and climate (temperature, rainfall, humidity, wind).

When classifying ecological factors, ask whether the factor involves a living organism or its activity (biotic) or a non-living physical/chemical condition (abiotic). Pests and diseases are always biotic because they involve living agents.