Notes+from+Food+Webs

Using EasyBib.com

Works Cited De, Ruiter Peter Cornelis, Volkmar Wolters, and John C. Moore. //Dynamic Food Webs: Multispecies Assemblages, Ecosystem Development, and Environmental Change//. Amsterdam: Academic, 2005. Print. Morse, Douglass H. //Predator upon a Flower: Life History and Fitness in a Crab Spider//. Cambridge, MA: Harvard UP, 2007. Print. Pimm, Stuart L. //Food Webs//. London: Chapman and Hall, 1982. Print. Quammen, David. //Monster of God: the Man-eating Predator in the Jungles of History and the Mind//. New York: W.W. Norton, 2003. Print.

(Pimm) Chapter 1 Food webs are highly patterned. Most populations are stable despite constant perturbations to their densities (growth rates/ resources on which species feed) Real systems cannot withstand perturbations as large as species removals, only relatively small perturbations are likely to shape webs selectively.

Limitation Hypotheses a) As food chain is ascended, rapidly attenuating energy flow precludes species feeding higher than a certain level b) It may be impossible to "build" a predator to feed on existing top predators c) There are always advantages to feeding as low in the food chain as possible d) Long food chains are dynamically fragile

Three food web features discovered statistically 1) The numbers of species of prey and predators are in the ratio of 3:4 2) There is a negative correlation between the number of predatory species which a species suffers and the number of species of prey which the species exploits 3) The patterns of overlap in the species of prey exploited by a set of predators can usually be expressed in one dimension.

There are important interrelationships between structure and function

Chapter 2: Models and their local stability

[Lotka-Volterra] 1) A predator's growth rate is determined by the abundance of prey 2) The prey's growth rate is determined by its food supply as well as the density of its predators 3) In some circumstances, predators only "skim off" the prey that are doomed to die from other causes and hence do not affect the growth rate of their prey (ex: Kruuk's work on the spotted hyena in the equatorial grassland of East Africa. The hyena has 3 main prey categories: very young animals, very old animals, the sick)

Two types of equations are used to develop mathematical models -differential equations for life cycles where populations overlap and death processes are continuous - difference equations for populations with distinct generations (ex: diapause in insect populations)

In Lotka-Volterra, predators exert a negative effect on the growth rate of their prey In donor-control model, the predators take only the prey which would die (or have died) from other causes. Systems are deemed stable when all species densities return to equilibrium following a perturbation The theorem of qualitative stability postulates that differential equation systems can be known to be stable irrespective of the magnitude of the interactions between species.

Species deletion is a relatively large perturbation ....more critically it is a persistent one. A system is said to be species deletion stable if, following the removal of a species from the system all of the remaining species are retained at a new, locally stable equilibrium. Natural systems may lose species through emigration, epidemics, increased vulnerability to predators, catastrophic destruction by weather or other physical factors, the agencies of man, and many other factors

Global stability implies a transient perturbation.

Return time is one measure of relative stability. Systems with short return times can be considered more resilient than those with long return times.

p.78 Which species can be removed without further losses of species from the web? The results for six-species models show thart species deletion stability averaged over all species change only slightly with increasing complexity. There are however marked differences depending on which species are deleted from the web. For the species at the base of the web, increasing complexity does increase species deletion stability. But, increasing complexity, rapidly decreases the chances that a model food web will persist in the absence of its top predators.

p.99 The energy which plants capture from the sun during photosynthesis may end up in tissues of a hawk via bird the hawk has eaten, the insects eaten by the bid, and the plant on which the insects fed. The plant-insect-bird-hawk system is called a food chain, and each stage a trophic level. More generally, the trophic levels are called producers (plants), herbivores or primary consumers (the insects), carnivores or secondary consumers (the bird) and top carnivores or tertiary consumers (the hawk).

p.105 The first law of thermodynamics states that the total amount of energy remains constant; when one animal eats a plant, the energy is merely converted from one form into another. But the second law of thermodynamics implies that energy cannot be converted from one form to another (from victim to consumer) without some of this energy being lost as heat-- the respiration term. This raises an obvious question: what fraction of the energy entering a trophic level...is available to the species at the next trophic level...

p.111 Predators must be 'fiercer' than their prey where ferocity involves a comploex of physical attributes (including size, strength, and speed) as well as behavioural ones. All these factors impose "design restrictions" on the species. Birds can only so large and still fly. Many of the largest flying predators (such as eagles) rely on thermals to keep them aloft, for their size precludes energetically expensive, flapping flight. That Peregrine Falcons and Gyrfalcons have no avian predators may well be because of the physical impossibility of having a winged predator fast enough to catch them and large enough to kill them.

p.112 Increased size also means increased energy requirements... The benefits of increased size comes from the animal's increased mobility. Larger animals roam over larger areas than smaller ones and have, as a consequence, at least the potential for increased supplies of energy

p.114 Size affects at least two important biological features: an animal's energy budget and its physical ability to perform the tasks necessary for its survival. Energetically, there are both disadvantages and advantages in being large: larger animals. need more energy but feed over larger areas than smaller animals.