chapter10predation

chapter10predation内容摘要：

se population 187。 Increased steadily in the 1960s and 1970s 187。 Declined as the wolf population increased until 1981 Field Studies of PredatorPrey Interactions – Moose population (cont.) 187。 A record population of 2500 was reached in 1995, when the wolf population was low 187。 Good evidence of prey population control by predators 187。 Confounded in 1996 when the moose population crashed starvation Field Studies of PredatorPrey Interactions – Canada lynx and snowshoe hare • Populations show dramatic cyclic oscillations every 9 to 11 years (Figure ) 20 40 60 80 100 120 20 40 60 80 100 120 140 160 180 200 Abundance of lynx Abundance of hares Abundance of lynx (x 1000) Abundance of hares (x 1000) 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 Field Studies of PredatorPrey Interactions – Canada lynx and snowshoe hare (cont.) • Cycle has existed as long as records have existed (over 200 years) • An example of intrinsically stable predatorprey relationship Introduced Predators • Method for determining the effects of predators • Dingo predations on kangaroos in Australia – Dingo • Introduced species • Largest Australian carnivore Introduced Predators – Dingo (cont.) • Predator of imported sheep • Eliminated from certain areas – Spectacular increases in native species 187。 160 fold increase in red kangaroos 187。 Over 20 fold increase in emus Introduced Predators – Dingo (cont.) • Effects on feral pigs – Shortage of young pigs – Considerable impact on recruitment of pigs (Figure ) 0 60 40 20 20 40 60 Age class (years) Males (%) Females (%) 0 60 40 20 20 40 60 Males (%) Females (%) 6+ 56 45 34 23 12 .05 6+ 56 45 34 23 12 .05 Age class (years) (a) Dingoes present (a) Dingoes present Introduced Predators • European foxes and feral cats in Australia – Damage domestic livestock – Effects when removed (Figure ) 0 20 40 60 Predators shot No shooting 1981 1982 Mean no. of rabbits per km of transect Introduced Predators • Lamprey and the Great Lakes – Construction of Wetland Canal allowed lamprey to enter the Great Lakes – Dramatic reduction in lake trout (Figure ) Lake Huron Mean production 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 Lake Michigan Lake Superior Mean production Mean production 1930 1935 1940 1945 1950 1955 1960 Lake trout production (millions per pound) Introduced Predators • Lamprey and the Great Lakes (cont.) – Trout recovered after lamprey population was reduced Field Experiments with Natural Systems • Lions in South Africa – Kruger National Park, 1903 – Lions Shot – Number of large prey increased – Shooting of lions ends, 1960 – Wildebeast increase so much that their numbers had to be culled from 1965 to 1972 Field Experiments with Natural Systems • Gray partridge, European game bird – Figure Field Experiments with Natural Systems • Gray partridge, European game bird (cont.) – Over 20 million shot in Great Britain in the 1930s – Only million shot in the mid1980s • High chick mortality due to starvation Field Experiments with Natural Systems – Only million shot in the mid1980s (cont.) • Reduced insects due to introduction of herbicides in the 1950s was suspected • However, smaller populations in areas where there was no control of predators by gamekeepers Field Experiments with Natural Systems – Only million shot in the mid1980s (cont.) • Predation control increased – The number of partridges 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。