BIO 101

Repeated production of offspring at intervals throughout the life cycle of an organism.
Condition of having a single reproductive effort in a lifetime.
Type I populations
type I survivorship curve
exhibited by population in which mortality rates rise steeply in post-reproductive years
also known as “late loss” curve
most individuals die in older age intervals
species with this type curve
produce few offspring & give them intense care to insure their survival
humans, whales, elephants
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Type II populations
type II survivorship curve
exhibited by population in which individuals are equally likely to die at any age
also known as “constant loss” curve
mortality is constant over life span
intermediate to types I and III
some rodents
Type III populations
type III survivorship curve
exhibited by population in which individuals produce vast numbers of offspring
also known as “early loss” curve
only a small number of offspring survive to reproductive age
survivors become established, reproductive, with low mortality rate
oysters, some plants
Density Dependent Factors
density-dependent factors
limits to growth related to population density
density-dependent factors
affect a greater percentage of individuals in a population as density increases
individuals compete with increasing intensity for limited resources
such as
Density Independent Factors
density-independent factors
population-limiting affects that are independent of population density
include abiotic factors
physical disruption of habitat
Prey Defense Mechanisms
Animal that could be prey, must constantly avoid being eaten. For this reason, these creatures have to resort to defense mechanisms. Examples of some defense mechanisms prey use are:
Chemical combat as some frogs use.
Camouflage like the chameleon use.
Speed as vegetarian animals run all day to avoid predators.
Trickery: false features and mimicry as butterflies do for surviving.
Life History
Life history of an organism
series of events from birth through reproduction to death
life history strategies influence growth rate of a population, including
age of first reproduction
number of offspring
amount of parental care given to offspring
energy cost of reproduction
shaped by evolution
operating through natural selection
every population has a life history strategy adapted to its environment
two main life history strategies
opportunistic (r-selected)
equilibrial (K-selected)
Opportunistic (r-selected) life history
put most of their energy into reproduction
rather than long term survival of individuals
are poor competitors
considered opportunists
take advantage of favorable conditions, changes in environment
when favorable conditions are gone population may crash
population go through irregular or unstable cycles
reproduce when young
produce many offspring
provide little to no parental care of offspring
most offspring die before reaching reproductive age
tends to grow exponentially
thus the name r-selected
due to high intrinsic rate of growth
live in unpredictable environments
controlled by density-independent factors
exhibit type III survivorship curve
most annual plants
most insects
equilibrial (K-selected) life history
put fairly little energy into reproduction
put most energy into long term survival
for purpose of being able to put lots of energy into nurturing and protecting offspring
are good competitors
are not considered opportunistic
thrive best in ecosystems with fairly constant environmental conditions
populations remain close to carrying capacity (K) over long periods of time
reproduce later in life
produce fewer offspring
provide high parental care
most offspring survive to reproductive age
size tends to be stable
thus the name K-selected
populations tends to stay near carrying capacity (K)
live in predictable environments
controlled by density-dependent factors
exhibit type I survivorship curve
large trees
polar bears
Intermediate life history
many organisms have life histories that fall between opportunistic and equilibrial
exhibit type II survivorship curve
many birds
Realized Niche
Realized niche width is a phrase relating to ecology defining the actual space that an organism inhabits and the resources it can access as a result of limiting pressures from other species (e.g. superior competitors).
Fundamental Niche
The fundamental niche is where a species CAN live, negating the effects of predation, resource limitation, etc.
The Arctic tundra biome, which encircles the Earth just south of ice-covered polar seas in the Northern Hemisphere, covers about 20% of the Earth’s land surface (Fig. 46.6). (As mentioned, a similar ecosystem, the alpine tundra, occurs above the timberline on mountain ranges.) The Arctic tundra is cold and dark much of the year. Arctic tundra has extremely long, cold, harsh winters and short summers (6-8 weeks). Because rainfall amounts to only about 20 cm a year, the tundra could possibly be considered a desert, but melting snow creates a landscape of pools and bogs in the summer. Only the topmost layer of soil thaws; the permafrost beneath this layer is always frozen, and therefore, drainage is minimal. The available soil in the tundra is nutrient-poor. Trees are not found in the tundra because the growing season is too short. The roots cannot penetrate the permafrost and they cannot become anchored in the shallow boggy soil of summer. In the summer, the ground is covered with short grasses and sedges, as well as numerous patches of lichens and mosses. Dwarf woody shrubs, such as dwarf birch, flower and seed during the short growing season.

A few animals live in the tundra year-round. For example, the mouselike lemming stays beneath the snow; the ptarmigan, a grouse, burrows in the snow during storms; and the musk ox conserves heat because of its thick coat and short, squat body. Other animals that live in the tundra include snowy owls, lynxes, voles, Arctic foxes, and snowshoe hares. In the summer, the tundra is alive with numerous insects and birds, particularly shorebirds and waterfowl that migrate inland. Caribou in North America and reindeer in Asia and Europe also migrate to and from the tundra, as do the wolves that prey upon them. Polar bears are common near the coastal regions. All species have adaptations for living in extreme cold with a short growing season.

Grasslands occur where annual rainfall is greater than 25 cm but generally insufficient to support trees. For example, in temperate areas, where rainfall is between 25 and 75 cm, it is too dry for forests and too wet for deserts to form.
Grasses are well adapted to a changing environment and can tolerate a high degree of grazing, flooding, drought, and sometimes fire. Where rainfall is high, tall grasses that reach more than 2 m in height (e.g., pampas grass) can flourish. In drier areas, shorter grasses (between 5 and 10 cm) are dominant. Low-growing bunch grasses (e.g., grama grass) grow in the United States near deserts.
The growth of grasses is seasonal. As a result, grassland animals such as bison migrate, and others such as ground squirrels hibernate, when there is little grass for them to eat.
Temperate Grasslands
The temperate grasslands include the Russian steppes, the South American pampas, and the North American prairies (Fig. 46.12). In these grasslands, winters are bitterly cold and summers are hot and dry. When traveling across the United States from east to west, the line between the temperate deciduous forest and a tall-grass prairie is roughly along the border between Illinois and Indiana. The tall-grass prairie receives more rainfall than does the short-grass prairie, which occurs near deserts.
Savannas occur in regions where a relatively cool dry season is followed by a hot rainy season (Fig. 46.13). The largest savannas are in central and southern Africa. Other savannas exist in Australia, southeast Asia, and South America. The savanna is characterized by large expanses of grasses with relatively few trees. The plants of the savanna have extensive and deep root systems that enable them to survive drought and fire. One tree that can survive the severe dry season is the thorny flat-topped Acacia, which sheds its leaves during a drought. The African savanna supports the greatest variety and number of large herbivores of all the biomes. Elephants and giraffes are browsers that feed on tree vegetation. Antelopes, zebras, wildebeests, water buffalo, and rhinoceroses are grazers that feed on the grasses. Any plant litter that is not consumed by grazers is attacked by a variety of small organisms, among them termites. Termites build towering nests in which they tend fungal gardens, their source of food. The herbivores support a large population of carnivores. Lions, hyenas, cheetahs, and leopards all prey upon the abundant
Deserts are usually found at latitudes of about 30°, in both the Northern and Southern Hemispheres. Deserts cover nearly 30% of the Earth’s land surface. The winds that descend in these regions lack moisture, resulting in an annual rainfall of less than 25 cm. Days are hot because a lack of cloud cover allows the Sun’s rays to penetrate easily, but nights are cold because heat escapes easily into the atmosphere.
The Sahara, which stretches all the way from the Atlantic coast of Africa to the Arabian peninsula, along with a few other deserts, have little or no vegetation. However, most deserts contain a variety of plants that are highly adapted to survive long droughts, extreme heat, and extreme cold (Fig. 46.14a). Adaptations to these conditions include thick epidermal layers, water-storing succulent stems and leaves, and the ability to set seeds quickly in the spring. The best-known desert perennials in North America are the spiny cacti, which have stems that store water and carry on photosynthesis. Also common are nonsucculent shrubs, such as the many-branched sagebrush with silvery gray leaves and the spiny-branched ocotillo, which produces leaves during wet periods and sheds them during dry periods. Some animals are adapted to the desert environment. To conserve water, many desert animals such as reptiles and insects are nocturnal or burrowing and have a protective outer body covering. A desert has numerous insects, which pass through the stages of development in synchrony with the periods of rain. Reptiles, especially lizards and snakes, are perhaps the most characteristic group of vertebrates found in deserts, but running birds (e.g., the roadrunner) and rodents (e.g., the kangaroo rat) are also well known (Fig. 46.14b). Larger mammals, such as the kit fox, prey on the rodents, as do hawks.
frequently or continually inundated by water characterized by the presence of rushes and reeds.
Swamps: dominated by woody plants or shrubs.
Bogs: acidic waters and peat deposits
Bogs: acidic waters and peat deposits

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