Trophic dynamics

What are the two trophic systems

Plant-based & detritus-based

What is the first trophic level in detritus-based systems

Microbes

Example of Botton-up control

N limits grass production which limits herbivores

How do trophic cascades work in top-down controls

Predators limit the density and/or behaviour of their prey thereby enhancing the survival of the next lower trophic level

Plants infected with AM fungi lead to…

higher prey quality which causes increased predator reproduction, intrinsic and finite rates of population increase

What did Hairston et al. (1960) propose

Animal predation is a key driver of vegetation structure, noted that herbivores must be limited by predators, proposed that without carnivores, herbivores would have a major impact on vegetation (green world to brown world)

Critiques on the green and barren world concept

Ignores plant defenses “the reason the world is green is because most plants are inedible”, assumes linear food chains but we know complex food webs often exist

Give example of green and barren world concept

Macquarie Island

Describe the Macquarie Island case study

In the 1990s the island had rabbits and cats. The cats kept the rabbit population in check allowing grasses to grow. In 2005 humans killed off the cats releasing rabbit populations which decimated grass creating a barren world. In 2014 all rabbits and cats were removes creating one trophic level which was green

How is fire similar to herbivory

Seasonal, selective, fluctuates in intensity, transforms nutrients

How is fire different from herbivory

Does not depend on vegetation nutritional quality (can consume vegetation that herbivores will not) but plants adapt to resist or cope with fire like with herbivory and can influence fire frequency and intensity

Consumption efficiency is low in what ecosystems

terrestrial ecosystems