Apex Predators

Apex predator

Top trophic position species in a community

Mesopredator

Species occupying trophic position below apex predators

Mesopredator release hypothesis

Increased mesopredator densities after apex predator removal

Mesopredator intraguild competition

Structure ecosystems along multiple food web pathways

Why do mesopredators have a "fluid role"

They can become apex predators via secondary mesopredator release

Secondary mesopredator release

When mesopredators become apex predators

Energetic constraints

Dietary limits affecting predator size and prey choice

Trophic cascades

Ecosystem changes triggered by species removal or addition

Demographic impacts of top-down trophic cascades

Population changes in prey due to predator presence/ absence

2 drivers of mesopredator release

Direct lethal encounters and indirect landscape of fear (leading to avoidance)

Why have we only just discovered mesopredator release

Historically we assumed that all predation is the same, and that humans can replace apex predators

Arguments for mesopredator replacement of apex predators

Coyotes form larger packs and hunt larger prey in the absence of wolves

Arguments against mesopredator replacement of apex predators

Mesopredators have different relationships between people and ecosystems than apex predators, and are usually omnivores

Optimal foraging theory

Organisms maximize net energy intake over time

Holling disc equation

E / h + s

What is E in hollings disc

energy in food item

What is h in hollings disc

handling time

What is s in hollings disc

search time

How do apex predators impose top-down control of ecosystems (2)

Demographic impacts (optimal foraging theory) and numerical responses (changing the number of prey)

Functional responses

Predator consumption rate changes with prey density

Type I functional response

Linear increase in intake rate with food density

Type II functional response

Decelerating intake rate at high prey densities (eg as food processing slows intake)

Type III functional response

S-shaped intake rate influenced by learning and prey switching

Landscape of fear

Prey behavior altered by perceived predation risk

Giving-up densities

Prey abandon patches based on maximising food intake rates

Risk allocation hypothesis

Trade-off between anti-predator behaviour and essential activities

Intraguild predation

Predation among species occupying similar trophic levels

Ecosystem services

Benefits provided by ecosystems, influenced by predators

Herbivore top-down limitation

Herbivore populations controlled by apex predators

Numerical responses

Predator density changes with prey density fluctuations

Cryptic nature of decline

Subtle declines in predator populations are hard to observe

Body mass ratio

Apex to mesopredator ratio must be 2-5.4:1.