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By the end of this section, you will be able to:
  • Discuss the predator-prey cycle
  • Give examples of defenses against predation and herbivory
  • Describe the competitive exclusion principle
  • Give examples of symbiotic relationships between species
  • Describe community structure and succession

Populations rarely, if ever, live in isolation from populations of other species. In most cases, numerous species share a habitat. The interactions between these populations play a major role in regulating population growth and abundance. All populations occupying the same habitat form a community: populations inhabiting a specific area at the same time. The number of species occupying the same habitat and their relative abundance is known as species diversity. Areas with low diversity, such as the glaciers of Antarctica, still contain a wide variety of living things, whereas the diversity of tropical rainforests is so great that it cannot be counted. Ecology is studied at the community level to understand how species interact with each other and compete for the same resources.

Predation and herbivory

Perhaps the classical example of species interaction is predation: the hunting of prey by its predator. Nature shows on television highlight the drama of one living organism killing another. Populations of predators and prey in a community are not constant over time: in most cases, they vary in cycles that appear to be related. The most often cited example of predator-prey dynamics is seen in the cycling of the lynx (predator) and the snowshoe hare (prey), using nearly 200 year-old trapping data from North American forests ( [link] ). This cycle of predator and prey lasts approximately 10 years, with the predator population lagging 1–2 years behind that of the prey population. As the hare numbers increase, there is more food available for the lynx, allowing the lynx population to increase as well. When the lynx population grows to a threshold level, however, they kill so many hares that hare population begins to decline, followed by a decline in the lynx population because of scarcity of food. When the lynx population is low, the hare population size begins to increase due, at least in part, to low predation pressure, starting the cycle anew.

The graph plots number of animals in thousands versus time in years. The number of hares fluctuates between 10,000 at the low points, and 75,000 to 150,000 at the high points. There are typically fewer lynxes than hares, but the trend in number of lynxes follows the number of hares.
The cycling of lynx and snowshoe hare populations in Northern Ontario is an example of predator-prey dynamics.

The idea that the population cycling of the two species is entirely controlled by predation models has come under question. More recent studies have pointed to undefined density-dependent factors as being important in the cycling, in addition to predation. One possibility is that the cycling is inherent in the hare population due to density-dependent effects such as lower fecundity (maternal stress) caused by crowding when the hare population gets too dense. The hare cycling would then induce the cycling of the lynx because it is the lynxes’ major food source. The more we study communities, the more complexities we find, allowing ecologists to derive more accurate and sophisticated models of population dynamics.

Questions & Answers

what is used to determine phylogeny?
Israel Reply
which condition is the basis for a species to be reproductively isolated from other members?
Israel Reply
Why do scientists consider vestigial structures evidence for evolution?
Israel
8.Which statement about analogies is correct?
Israel
What is true about organisms that are a part of the same clade?
Israel
Why is it so important for scientists to distinguish between homologous and analogous characteristics before building phylogenetic trees?
Israel
(CH2O)n is the stoichiometric formula of
Marcellus Reply
what are nucleotide
Anastijjaninaiya Reply
Methane,ammonia,water and sugar are dissolved to form nuceotide
Me
Introduction To Biology
Tanveer Reply
can ringworm be caused by bacterium
fred Reply
Nope
ejikeme
Branches of biology
Tanveer
no it does not occurs by bacterium
gopal
what is a brick?
Istifanus Reply
what is gene in biology?
yousaf Reply
it is a heredity unit
Me
what is DNA
yousaf Reply
carrier of genetic information
missy
deoxyribonucleic acid
gopal
it contains genetic information and brings it to one generation to other
gopal
it is of two Types circular DNA and linear DNA
gopal
plasmids are the type of small circular DNA which lies outside the genomic DNA
gopal
And what makes a virus to be difficult to destroy
Mosongo
what observation is made when dry seeds and soaked seeds are put in a vacuum flask
Robin Reply
there is respiration from the soak seeds which shows on the walls of the vacuum flask
Israel
what's mammals ?
Istifanus Reply
mammals are vertebrates ,any member group of vertebrates animals in which the young are nourished with milk from special mammary glands of the mother.
yousaf
what are actin and myosin
Praveen Reply
they are muscle filaments
Israel
they make up the microfibrils of the muscle ,relaxing and contracting to cause movement
Israel
Please did anybody know the questions that will come out in the coming practical?
Oladimeji
Why it is importantthat there are different types of protein in plasma membraine for the transport materials into and out of a cell?
Louellie Reply
the nerve cell
Mustapha Reply
differences between Homo sapiens and other primates
Aphiwe Reply
Why is albinism a recessive trait
Bright
Tyrosinase gene are make albinism to recessive trait
vinod
And what are the Tyrosinase genes
Bright

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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