Food Webs

Food webs are sometimes simplified (conceptually) to the drama of a single predator-prey interaction

but, these are the (proverbial) tip of the iceberg. Ecological community interactions are extremely complex…

Most food web are extremely complex

…and our understanding of virtually all food webs is incomplete

Herbivores, that are competing, and also prey items

Predators, that are NOT directly interacting, but are interacting

Here is the ecological story: In competition, the larger Daphnia will outcompete the smaller Daphnia. The salamanders eat the larger Daphnia, allowing the smaller Daphnia to persist. The midge can ONLY eat the smaller Daphnia. Thus, where the salamander larva is present, the midge larva do well… because they control the population of the midge prey’s competitor.

Food web interactions can be:Direct and/or indirect. Acute and/or chronic.Spatially distinct and/or diffuse.Multigenerational and/or unique to a particular moment in time

How are communities regulated?

Top-down regulation, keystone predators and the trophic cascade

Regulation of community structure…

Keystone...

Pisaster: The quintessential Keystone Predator!?

Robert Paine (1969)

Removing the starfish resulted in a massive change in the diversity of the system wherein one species crowded out others

Top-down regulation, keystone predators and the trophic cascade.

Are all different terms for the same effect. Predators control the food web structure through predation. Trophic cascade is particularly, and specifically, focused on the influence of predators controlling food web structure from the top of the food web.

Regulation of community structure…

Keystone predators

Yellowstone wolves control elk populations in two important ways:

1)Elk population numbers are reduced

2)Modify elk behavior

http://www.pbs.org/wgbh/nova/wolves/lonesome.html

The Ecology of Fear

http://www.pbs.org/wnet/nature/episodes/in-the-valley-of-the-wolves/video-wolves-on-the-hunt/220/

Bottom-up regulation…Primary producers drive community structure?

Regulation of community structure…

Bottom-up regulation…Primary producers drive community structure?

Regulation of community structure…

Keystone Herbivore?

Regulation of community structure…

Madagascar Flying Fox:

A Keystone Seed Disperser?

Regulation of community structure…

Beaver- A keystone landscape engineer???

Food webs are multifaceted

Shall we assume that time stands still?

Food Webs