Lions, hyenas, wolves, dholes, African wild dogs, and piranhas can kill large herbivores that single animals of the same species could never dispatch. Social predation allows some animals to organize hunts of creatures that would easily escape a single predator Size-selective predation involves predators preferring prey of a certain size. Large prey may prove troublesome for a predator, while small prey might prove hard to find and in any case provide less of a reward.
This has led to a correlation between the size of predators and their prey. Size may also act as a refuge for large prey, for example adult elephants are generally safe from predation by lions, but juveniles are vulnerable. How is social predation different from size-selective predation? Search and find II. Camouflage consists of not only color, but also shape and pattern.
The background upon which the organism is seen can be both its environment e. The more convincing camouflage is, the more likely it is that the organism will go unseen. Mimicry is a related phenomenon where an organism has a similar appearance to another species. One such example is the drone fly, which looks a lot like a bee, yet is completely harmless as it cannot sting at all III. Ecological role Predators may increase the biodiversity of communities by preventing a single species from becoming dominant.
Such predators are known as keystone species and may have a profound influence on the balance of organisms in a particular ecosystem. Introduction or removal of this predator, or changes in its population density, can have drastic cascading effects on the equilibrium of many other populations in the ecosystem.
For example, grazers of a grassland may prevent a single dominant species from taking over.
The Wolf and the Moose: Natural Enemies That Need Each Other
The elimination of wolves from Yellowstone National Park had profound impacts on the trophic pyramid. Without predation, herbivores began to over-graze many woody brow species, affecting the area's plant populations. Additionally, wolves often kept animals from grazing in riparian areas, which protected beavers from having their food sources encroached upon. They all conspired against the moose population which collapsed in Another decade passes Moose continue to dwindle.
Ina wolf immigrates from Canada, bringing an infusion of new genes. The wolves increase erratically. After 53 years The wolf population eventually stumbles as the moose continue to be kept low by high rates of predation, ticks, and hot summers. Much of what we have learned is associated with having been patient enough to observe and study the fluctuations in wolf and moose abundances summarized above.
The wolves and moose of Isle Royale also frequently reveal intimate details of their daily life experiences and they have inspired numerous artistic expressions. If we pay attention, they all tell us something important about our relationship with nature. These insights and discoveries are all presented here for you. Building on the graph above and to develop a deeper understanding, here is more on the history of wolves and moose on Isle Royale. Moose first came to Isle Royale in the early 20th century, and for fifty years, their numbers fluctuated with weather conditions and food abundance.
Wolves first arrived in the late s by crossing an ice bridge from Canada. The lives of Isle Royale moose would never be the same. Researchers began annual observations of wolves and moose on Isle Royale in The project began during the darkest hours for wolves in North America—humans had driven wolves to extinction in large portions of their former range. The hope had been that knowledge about wolves would replace hateful myths and form the basis for a wiser relationship with wolves.
Most studies in ecology last for a few years or less. Afterward, ecologists naturally draw conclusions about the nature of our environment. Scientists did so after observing the wolves and moose of Isle Royale for a few years. Durward Allen, who initiated the Isle Royale wolf-moose project inwas a pioneer among ecologists for having the foresight to understand the value of continuing to observe where others would have drawn conclusions and moved on to study something different.
By the moose population had doubled, and one now had to admit there had been a major shift in the balance. The wolf-moose project was originally designed to continue for ten years.
Administrators of the day suggested that the project end. Durward found greater merit in continuing to lead these observations. Bythe study in its 22nd year, the moose population had tripled from its original size and then declined to half its maximum size. During that time, wolves more than doubled to fifty.
By now it was apparent. In particular, wolves in were abundant and moose had been on the decline for the better part of a decade. Would it be possible that wolves could drive their prey to extinction? No one had ever observed wolves and their prey long enough to know. The next two years were dramatic.
Wolf & Moose Populations - Isle Royale National Park (U.S. National Park Service)
Wolves plummeted from 50 to Canine parvovirus, a disease inadvertently introduced by humans, was largely to blame for the decline. With only 14 wolves, extinction was a real concern. The only way to know what would happen next would be to continue observing. The wolf population recovered partially during the mids, only to decline again.
For much of a decade wolf abundance remained in the low teens. It seemed plausible, but far from certain, that the low numbers were ultimately the negative consequences of inbreeding.
All we knew for sure was that Isle Royale wolves are highly inbred and descended from just a single female and two males. Low wolf abundance provided an unprecedented opportunity — a natural experiment of sorts — to see how moose would respond to reduced wolf predation. With predation low during the late s and early s, moose lived longer and gave birth to more calves.
The moose population nearly tripled to almost 2, by During the winter oflack of forage for the moose, an outbreak of moose ticksand severe winter all conspired against the moose. The winter had been more severe than any in over a century. The moose population collapsed from its all-time high to just moose. Just as the moose population collapsed, wolves seemed as though they would stage a comeback — their abundance doubled in the mid s.
With the collapse of the moose population, food for wolves was rare, and the timing of their comeback unfortunate. What happened next is something we would not discover ourselves for another 14 years.
During the winter ofa wolf from Canada immigrated to Isle Royale.