【正文】 ges that bred successfully – The average size of the broods – Partridge populations by 75 % Field Experiments with Natural Systems ? Predators and rodents in Finland – Large scale removal of predators, April 1992 and 1995 over 23 km2 – Large increase in rodent population by June (pared to control plots) (Figure ) April June April June 3 2 1 0 3 2 1 0 Without predators With predators Mean number of rodents per sample Mean number of rodents per sample Applied Ecology ? Humans as predators whaling – Exploitation necessary – Is harvesting at any level sustainable? ? History of Antarctic whaling – Figure 1 Applied Ecology ? History of Antarctic whaling (cont.) – 1930s, blue whales primarily harvested – 1950s, blue whale population depleted, replaced with fin whale – 1960s, fin whale population collapsed Applied Ecology ? History of Antarctic whaling (cont.) – 1960s, humpback whale population collapsed – Prior to 1958, Sei whales hardly ever harvested ? Reduction in other whales made Sei whale attractive Applied Ecology – Prior to 1958, Sei whales hardly ever harvested (cont.) ? Peak harvest of about 20,000 by 196465 ? Catches declined thereafter due to limitations – The relatively small minke whale ? Was ignored in the southern oceans until 197172 Applied Ecology – The relatively small minke whale (cont.) ? Began to be taken, and is now the largest ponent of the southern baleen whale catch – Whale ban proposed in 198586, took effect in 1988 Applied Ecology – Iceland, Norway, and Japan, 1994 ? Argued for resumption of limited mercial whaling ? Should we ban mercial whaling? ? Whale populations are recovering Applied Ecology ? Whale populations are recovering (cont.) – Ex. Blue whale populations have increased four fold – Ex. California grey whales have recovered to prewhaling levels Summary ? Predation is a strong selective force in nature – Aposematic coloration – Camouflage – Batesian and Mullerian mimicry – Intimidation displays – Polymorphisms Summary ? Predation is a strong selective force in nature (cont.) – Chemical defenses ? Modeling predatorprey interactions – Even simple predatorprey models show Summary – Even simple predatorprey models show (cont.) ? Stable cycles ? Wildly increasing and unstable oscillations – Difficulty in predicting or modeling how predators and prey interact ? Mutual interference between predators Summary – Difficulty in predicting or modeling how predators and prey interact (cont.) ? Existence of specific predator territory sizes ? Ability of predators to feed on more than one type of prey Summary ? Largescale observations support – Predators only take weak and sickly individuals – Prey populations influence predator numbers, not vice versa Summary ? Accidental or deliberate introductions of exotic predators – Profound effects on native prey populations – Predators have important regulatory effects on prey Summary ? Accidental or deliberate introductions of exotic predators (cont.) – May not be indicative of “natural systems” Summary ? Evidence from natural systems – Most studies have concluded that predators have a significant effect on prey Discussion Question 1 ? Should ranchers be concerned about the reintroduction into their vicinity of large predators, like wolves and panthers? Discussion Question 2 ? Do sea lions, otters, or dolphins decrease the stock of fish available for people that fish? Discussion Question 3 ? Would the number of deer available for hunters be the same in the presence of large predators? Discussion Question 4 ? What data would you need to collect to answer the above 3 questions? Discussion Question 5 ? What can the effects of exotic predators tell us about the strength of predation? What can39。s predator and prey isoclines have? What would these shortings mean in terms of determining how predators and prey interact? Discussion Question 8 ? A great many fish stocks seem to have been overfished. How do you think we could prevent overfishing? What biological information do we need to have, and how can we get it when we can39。Carrying capacity changes 187。 low at low prey densities, but increases quickly at high densities – Changes in prey consumption ? Functional response changes (Figure ) PredatorPrey Models ? Functional response changes (cont.) – Dictates how individual predators respond to prey population ? Numerical response changes – Governs how a predator population migrates into and out of areas in response to prey densities Field Studies of PredatorPrey Interactions ? Field parisons to models ? Do predators control prey populations? ? Importance of predators in controlling prey density – Kaibab deer herd ? Kaibab Plateau (Northern Arizona) Field Studies of PredatorPrey Interactions – Kaibab deer herd (cont.) ? Declared a national park around 1900 ? All big predators were removed and deer hunting was prohibited ? Estimates of 10 fold increase in deer population ? Reevaluated by Graham Caughley (1970) Field Studies of PredatorPrey Interactions ? Reevaluated by Graham Caughley (1970) (cont.) – Predator control had some impact。s Isle Royale Field Studies of PredatorPrey Interactions – Moose population on Michigan39。Peaked at 50 in 1980 187。Small recovery in the late 1990s – Moose population 187。Declined as the wolf population increased until 1981 Field Studies of PredatorPrey Interactions – Moose population (cont.) 187。Good evidence of prey population control by predators 187。160 fold increase in red kangaroos 1