Species Interactions: Predation

Species Interactions: Predation

• Predation is a trophic interaction where one species, the predator, consumes another, the prey.
• Predation includes carnivory (predator and prey are both animals), omnivory (animal or plant predator, and animal/plant prey) and herbivory (animal predator eating plant prey). Parasitism (parasite predator and host prey) is also included.
• Carnivores typically kill their prey. Herbivores, however, usually do not kill the plants.

Key Differences Between Carnivores and Herbivores

• Carnivores often kill their prey immediately, while herbivores usually do not kill the plants directly.
• Animal prey can move away or hide from predators, often escaping. Most plant prey cannot hide or escape.
• Plant prey is usually plentiful but less nutritious compared to animal prey because they have lower nitrogen content.
• Carnivores are generally generalists while herbivores are often specialists, feeding on specific parts of plants or prey.

Carnivory

• Carnivory is the consumption of animal prey by an animal predator.
• Adaptations for hunting include stealth (owls), speed (cheetahs), morphological adaptations (snakes), and venom (vipers).
• Predators who sit and wait employ adaptations like building traps (antlions) and mimicry (scorpionfish).

Herbivory

• Herbivory is the consumption of plants by animals.
• Adaptations for herbivory include behavioral adaptations (e.g., Bursera beetle larvae) and digestive tracts that accommodate secondary compounds or mechanical deterrents (e.g., spines).

Predator-Prey Population Cycles

• The Lotka-Volterra model, dN/dt = rN – aNP and dP/dt = baNP− mP, assesses predator-prey population dynamics. In the equation, N is the number of prey individuals, and P is the number of predator individuals.
• When predators are absent, prey should experience exponential growth.
• When prey are present, the predator population will increase proportionally to the amount of prey available. The efficiency with which predators capture their prey is a factor in their population increase, signified by the constant a.
• Predators starve if no prey is present; thus, their population declines exponentially if there's no prey, and a mortality rate is involved.

Effects of Predation on Communities

• Carnivores and herbivores can change the composition of a community.
• Case study examples include Anolis lizards in the Bahamas and Lesser snow geese.
• Intermediate grazing has a positive effect on the community, resulting in the highest Net Primary Productivity (NPP). Abundant prey leads to an increase in predators, which in turn lowers prey numbers. This causes the prey population to decline while the predator population increases.
• However high prey populations can also have a detrimental impact on the community. For example, the rise of the snow goose population led to a significant decline in plant life and made the marshes into mud flats.