Phase Diagram The standard LV oscillation where the

Phase Diagram The standard L-V oscillation where the predator lags behind the prey

Phase Diagram

Use Populus and Living Graphs (web site) to determine how sensitive the model is to changes in values for the different parameters Note when interactions become unstable.

Do predators ever exploit prey in nature and cause their extinction?

Human introduction of the Nile Perch (for food) into east African lakes caused extinction of > 100 endemic fish species! Ricklefs 2001 Fig. 1. 21

Ecologists searched for evidence of population cycles: Gause (1934) was the first to conduct experiments

Gause’s Experiments Hypothesis: two populations would oscillate continually in a nutritive media N 0 15 Time (days)

Gause’s Experiment • Predator efficiency was very high • Predators quickly found & ate all the prey • Result was an unstable interaction leading to the test tube extinction of both species

Gause’s Second Experiment Gave a “refuge” (glass wool) to the prey Glass wool

WITH A REFUGE. . . N Time

The expectation was cycles of abundance between predators & prey Therefore, this experiment also failed to support that prediction (the hypothesis was rejected). In a final experiment, Gause allowed “immigration” into the test tube by adding predators & prey when they dropped to low numbers

WITH “immigration”. . . N Prey Predator Time 15 days Now, coupled oscillations were observed

Gause’s experiments have an important message. . . • Simple, closed predator-prey systems are fragile & prone to extinction • High predator efficiency is destabilizing or disruptive • Refuges for prey delay or prevent extinction

Gause thought his experiments proved that cycles were rarely to be expected Huffaker (1954) thought that Gause was being too harsh in his criticism of the idea. Huffaker set up experiments in very complex habitats

Huffaker’s experiments were conducted in the “orange ecosystem” with predator & prey mites. Mites lived on oranges. Prey ate the oranges. Predators ate the prey. 4 oranges distributed at random among 40 locations Rubber balls Ricklefs 2001 Fig. 18. 6

Predator & prey mites in the “orange ecosystem” N 3 Time (weeks) 6

Huffaker was surprised by the results He thought that “complexity” would confer “stability” on the interaction. He thought both would persist & that the predator would not kill all the prey on all the patches at the same time. He persisted. . .

Huffaker next: Increased spatial complexity (120 positions) Vaseline barriers to slow “walking” predators Added dowels to aid dispersal of prey that spun silk to parachute to new locations. Fan provided wind.

Huffaker’s results: cycles occurred in complex systems Prey had the advantage in migration While local populations went extinct, others were established Ricklefs 2001 Fig. 18. 7

Results of both Gause & Huffaker show: 1. Immigration among patches is necessary to counteract local extinctions. 2. Spatial complexity (refuges, patches) favours persistence

E. F. Haskell 1949. A clarification of social science. Main Currents in Modern Thought 7: 45 -51 Species Interactions or coactions: • Helpful • Harmful • Neutral

Haskell’s Gain/Loss Matrix GAME BOARD: Species Interactions __ 0 + Species 2 __ Species 1 0 +

GAME BOARD: Species Interactions Species 1 __ competition 0 amensalism predation parasitism + Species 2 __ 0 + neutralism commensalism mutualism

A. Negative or neutral effects: competition (- -) amensalism (0 -) neutralism (0 0) B. Benefits to at least 1 species: mutualism (+ +) commensalism (+ 0) predation/parasitism (+ -)

It is not always clear if the effects are on the INDIVIDUAL or the POPULATION and if on the population, if the effect is on… - population size - growth

IA (interactions) not always obvious: Cattle grazing on grass? + /- OR +/+ ?

Range Management: Grazed grassland produces more biomass in a year than ungrazed grassland (+ +) Grazing provides faster cycling of nutrients (feces, bits of grass) results in fast return of nutrients to the soil.

GAME BOARD: Species Interactions Species 1 __ competition 0 amensalism predation parasitism + Species 2 __ 0 + neutralism commensalism Symbiotic mutualism Non- symbiotic

Mutualism: interaction between 2 or more spp that is of benefit to both or all. Symbiotic mutualism (close physical contact): partners can’t live without one another (obligate mutualism) Examples?

Examples: - alga & fungus form lichen +fungus gets food from algae +algae gets water & protection from desiccation - digestion of cellulose by microorganisms living in the guts of herbivores (termites to hippopotamuses) - nitrogen-fixing bacteria & plants plant gets nitrogen (fertilizer) bacteria gets food

Non-symbiotic mutualism http: //www. globaldialog. com/~jrice/fish_page/cleaner. htm

Ricklef’s Ch 17 “All life forms are both consumers and victims of consumers” • Describes herbivores as “predators” and “parasites” Grazers of herbacious plants Browers of woody plants

Adaptation of predators for exploiting prey. Incisors cut plants Flat molars & premolars grind plants Canine teeth & knife-edged premolars tear flesh