Predator -prey relationship
Mathematical models of predation are amongst the oldest in ecology. The idea that a coupled system of predator and prey would cycle gained further support . those of the boreal forest and tundra, although this no longer seems the rule. Predator and Prey relationships. Polar bear/Arctic fox; Arctic Wolf/Caribou; Brown bear/Arctic hare; Snowy owl/lemmings; Musk ox/Grasses Key: Predator/Prey. Living organisms in any biome interact through a variety of relationships. Organisms compete for food, water, and other resources. Predators hunt their prey.
However, time series of plant production indices from the arctic region are generally shorter than population time series for many animals, and for this reason, formal statistical evidence for multiannual plant cycles is currently missing. We will return to plant production cycles when discussing food web dynamics and how cycles may be generated. Invertebrates Population cycles of herbivorous insects are commonplace and ecologically important in forest ecosystems Berryman This contrasts with the situation on arctic tundra, where herbivorous insects are relatively unimportant in terms of abundance and ecosystem impact MacLean The bulk of terrestrial arctic invertebrates are found in the soil, where they play a crucial role as decomposers detrivores of dead organic material detritus.
To our knowledge, there are no population time series of sufficient length to examine whether there are multiannual population cycles present in arctic soil invertebrates. We suspect, however, that such population cycles exist, because cyclic lemmings' burrowing activity, disposal of dead plant material, and excreta have a great impact on soils. Lemmings and voles Lemmings and voles are disproportionally common on the tundra relative to other ecosystems.
Voles are represented mainly by species of the genus Microtus in the low-arctic tundra subzone. Two genera, Lemmus and Dicrostonyx, represent the lemmings, with five and two species, respectively. There is never more than one lemming species of each genus present at the same location Stenseth and Ims Lemmus species are distributed mainly in the low- to middle-arctic tundra subzones, whereas Dicrostonyx can be found all over the tundra and as far north as vascular plants exist.
Voles and lemmings are small herbivores the adult body size is 40 to grams that subsist on a diet of grasses, sedges, and herbs Microtus ; sedges and mosses Lemmus ; or herbs and dwarf shrubs Dicrostonyx Batzli et al.
Arctic lemmings and voles are active year-round under the snow in winter and have a very high metabolic rate Batzli et al. The combination of high metabolic rate and low digestive efficiency requires a high rate of food intake. A Norwegian lemming Lemmus lemmus may consume eight times its own body weight per day Stenseth and Ims The maximum reproductive rate of voles and lemmings is impressive: A female Norwegian lemming can become pregnant as soon as she is weaned 16 days old. Pregnancy lasts 20 days, and each litter normally contains 5 to 7 young with a maximum of Only a few hours after a female has delivered a litter, she often mates again.
The breeding season can commence under the snow in the middle of the winter and last until the next fall. It is thus conceivable that a lemming population could increase from less than one individual to several hundred individuals per hectare ha in 2 years Stenseth and Ims The maximum reproductive potential is rarely attained in the field, however, and there are large differences in the realized reproductive rate between seasons, years, and species.
Lemming cycles usually exhibit a statistical periodicity mean interval between peak years of around 4 years figure 1 ; Stenseth At locations with more than one species of lemming or vole, the different species cycle in synchrony Stenseth and Ims Within the same species, population cycles can be synchronized over large areas Krebs et al.
Vole species with a wide geographic distribution tend to exhibit their most pronounced population cycles at northern latitudes boreal forest, northern alpine areas, and tundra Hansson and Henttonen To our knowledge, noncyclic lemming populations in the Arctic have so far been found at only one location, in arctic Canada Reid et al.
Arctic foxes, weasels, and ermine Three circumpolar predatory mammals exhibit cyclic population dynamics on arctic tundra: In inland tundra regions, the arctic fox belongs to the terrestrial ecosystem, preying mainly on lemmings Elton In lemming peak years, the arctic fox responds with high pregnancy rates and large litter sizes.
In coastal habitats, arctic foxes prey opportunistically on the much more stable components of the marine ecosystem, such as seabirds and carrion from sea mammals. Coastal foxes have lower pregnancy rates, and smaller and less variable litter sizes, than inland lemming foxes, which leads to more stable population dynamics. The small mustelids of the tundra, the ermine and the weasel, are not much larger than their rodent prey.
In fact, least weasels in Fennoscandia are considerably smaller than adult Norwegian lemmings. As a result of their small size, weasels and ermines can hunt in the burrows of small rodents year-round, and for that reason they are supposed to be the most efficient of all predators on lemmings and voles Oksanen et al. A weakness of our present knowledge of the role of small mustelids in arctic ecosystems is that no quantitative population data e.
Owls, raptors, and jaegers A species-rich guild of arctic avian predators preys on lemmings and voles Wiklund et al. The guild includes two owls, the snowy owl Nyctea scandiaca and the short-eared owl Asio flammeusand one raptor, the rough-legged buzzard Buteo lagopus ; all three species depend heavily on small rodents.Predator Prey Interactions - Basic Ecology -
The diet is more flexible in the jaegers, which are represented by three species: The jaegers live a dual life. In the winter they are marine birds at more southern latitudes, whereas in spring they migrate north to become a part of the tundra food web during the summer breeding season.
The owls and the rough-legged buzzard prey on small mammals year-round, but only the snowy owl may stay in the Arctic during the winter. The lemming cycle is reflected in the breeding density and success of these birds. During the low phase of the lemming cycle, very few predatory birds appear on their breeding ground. Snowy owls, short-eared owls, and rough-legged buzzards may not appear at all Batzli et al.
However, in lemming peak years, breeding pairs of predatory birds with large clutches abound on the tundra. Thus, the numerical response is to some extent due to high production of young. However, the main reason for the rapid numerical response e. Ptarmigan, geese, and shorebirds Ptarmigan Lagopus spp. The cycle period and amplitude for ptarmigan vary widely between geographic regions. An analysis of the numbers of snowshoe hares, and one of their main predators, the lynx, provides a remarkable record of a predator-prey cycle.
Peaks and valleys can be easily observed at roughly year intervals. Logic and mathematical theory suggest that when prey are numerous their predators increase in numbers, reducing the prey population, which in turn causes predator number to decline. The prey population eventually recovers, starting a new cycle. T Paramecium, which also proved useful in test-tube studies of competition, was placed in culture with a predaceous protozoan.
These laboratory studies found that cycles were short-lived, and the system soon collapsed. However, if one added more paramecium every few days, the expected cycle was observed. These results suggested that the predator-prey system was inherently self-annihilating without some outside immigration. The question then arose: Observing that frequent additions of paramecium produced predator-prey cycles in a test-tube led to the idea that in a physically heterogeneous world, there would always be some pockets of prey that predators happened not to find and eliminate.
Perhaps when the predator population declined, having largely run out of prey, these remaining few could set off a prey rebound. Spatial heterogeneity in the environment might have a stabilizing effect.
A laboratory experiment using a complex laboratory system supports this explanation. A predaceous mite feeds on an herbivorous mite, which feeds on oranges. A complex laboratory system completed four classic cycles, before collapsing.
Observations of prickly pear cactus and the cactus moth in Australia support this lab experiment. This South American cactus became a widespread nuisance in Australia, making large areas of farmland unusable. When the moth, which feeds on this cactus, was introduced, it rapidly brought the cactus under control.
Some years later both moth and cactus were rare, and it is unlikely that the casual observer would ever think that the moth had accomplished this. Once the cactus became sufficiently rare, the moths were also rare, and unable to find and eliminate every last plant. Inadequate dispersal is perhaps the only factor that keeps the cactus moth from completely exterminating its principal food source, the prickly pear cactus.
Prey defenses can be a stabilizing factor in predator-prey interactions. Predation can be a strong agent of natural selection. Easily captured prey are eliminated, and prey with effective defenses that are inherited rapidly dominate the population. Examples include camouflage in the peppered moth, and prey that are nocturnal to escape detection.
Tundra is also found to a limited extent in Antarctica — specifically, the Antarctic Peninsula. It extends south to the edge of the taiga a biome characterized by coniferous forests. The division between the forested taiga and the treeless tundra is known as the timberline or tree line.
Location of arctic tundra across the Northern Hemisphere. The tundra is known for cold conditions, with an average winter temperature of degrees F degrees Cand an average summer temperature ranging from 37 degrees to 54 degrees F 3 degrees to 12 degrees C.
The growing season lasts from 50 to 60 days.
Life in the Tundra — Tundra: Life in the Polar Extremes — Beyond Penguins and Polar Bears
The biome is also characterized by desertlike conditions, with an average of six to ten inches 15 to 25 cm of yearly precipitation, including snow melt. Winds often reach speeds of 30 to 60 miles 48 to 97 km an hour.
Another hallmark of the tundra is permafrost, a layer of permanently frozen subsoil and partially decayed organic matter. Only the top nine or ten inches of soil thaw, leading to the formation of bogs and ponds each spring.
Ice wedges in the permafrost can crack and cause the formation of polygonal ground. This picture also illustrates the formation of ponds as the snow melts each spring.
Photo courtesy of U. Fish and Wildlife Service. Warming Arctic temperatures due to climate change are causing the permafrost to thaw, releasing the carbon in the form of carbon dioxide a greenhouse gas. Additional carbon dioxide in the atmosphere will intensify warming, leading to increased thawing and the release of even more carbon dioxide.
This positive feedback loop thus has the potential to significantly increase the rate and effects of climate change.
Approximately 1, species of vascular plants are found across the Arctic tundra, including flowering plants, low shrubs, sedges, grasses, and liverworts. Lichens, mosses, and algae are also common. In general, tundra plants are low growing, have shallow root systems, and are capable of carrying out photosynthesis at low temperatures and with low light intensities. Animals found in the Arctic tundra include herbivorous mammals lemmings, voles, caribou, arctic hares, and squirrelscarnivorous mammals arctic foxes, wolves, and polar bearsfish cod, flatfish, salmon, and troutinsects mosquitoes, flies, moths, grasshoppers, and blackfliesand birds ravens, snow buntings, falcons, loons, sandpipers, terns, and gulls.
Reptiles and amphibians are absent because of the extremely cold temperatures.