Significant Ideas

• A species interacts with its abiotic and biotic environments; its niche is described by these interactions.

• Populations change and respond to interactions with the environment.

• A system has a carrying capacity for a given species.​

Things I Should Know

2.1.1 A species is a group of organisms that share common characteristics and that interbreed to produce fertile offspring. 

You need to address this topic in the context of named species. For example, use “Baltimore oriole” instead of the generic bird term, “Kentucky bluegrass” rather than “grass” and “silver birch” rather than “tree”

The definition of a species might seem simple, but it can be complex. There are many examples of instances where it is difficult to apply the above definition. Many bacteria reproduce mainly asexually. The definition of a species as a group of interbreeding individuals cannot be easily applied to organisms that reproduce only or mainly asexually. 

2.1.2 A habitat is the environment in which a species normally lives.

A habitat is an ecological or environmental area that is inhabited by human, a particular species of animal, plant, or other type of organism. It is a place where it can find food, shelter, protection and mates for reproduction. It is the natural environment in which an organism lives, or the physical environment that surrounds a species population.

​Be aware that for some organisms, habitats can change over time as a result of migration.

2.1.3 A niche describes the particular set of abiotic and biotic conditions and resources to which an organism or population responds

2.1.4 The fundamental niche describes the full range of conditions and resources in which a species could survive and reproduce.  The realized niche describes the actual conditions and resources in which a species exists due to biotic interactions.

Every organism is adapted to environmental conditions in its habitat. The role that an organism plays in nature is called ecological niche. For an animal, that niche includes things like its behavior, the food it eats, and whether it is active at night or in the day. In an ideal situation without interspecific competition, an animal could utilize every resource within its niche to its fullest ability. This niche that exists in the absence of competition from other species is called a species' fundamental niche. 

However, it sometimes faces competition with other species that limits the conditions under which it can exist. Every organism, whether an apex predator, like a lion, or a bacterium living in a hippo's intestinal tract, is likely to face competition from other species. Competition limits the potential resources available to a species, and in turn, restricts that species niche. The actual niche that a species fills in the face of interspecific competition is called its realized niche.

image from www.quia.com

2.1.5 The non-living, physical factors that influence the organisms and ecosystem - such as temperature, sunlight, pH, salinity and precipitation - are termed abiotic factors

2.1.6 The interactions between the organisms - such as predation, herbivory, parasitism, mutualism, disease and competition - are termed biotic factors.

Competition between members of the same species is Intraspecific competition. Individuals of the different species, competing for the same resources is called Interspecific competition.The other outcome is that one species may totally out compete the other, this is the principle of Competitive exclusion.

There are many different types of relationships that occur in nature.

Predation - one species feeds on another which enhances fitness (ability to pass on genetic traits) of predator but reduces fitness of prey. Herbivory is a form of predation.

Herbivory - the act of eating plants and a herbivore is an animal that eats plants. Herbivores play an important role in the ecology of any area, influencing plant communities and individual plant growth. 

Parasitism - The host provides a habitat and food for the parasite, but in return, the parasite causes harm (death, stunted growth, susceptibility to disease) in the host.  

Mutualism - A type of symbiotic relationship in which both species benefit from the relationship.

Disease - a particular abnormal condition, a disorder of a structure or function, that affects part or all of an organism. includes organisms such as viruses, bacteria, fungi and parasites that cause disease. 

Competition - the relationship between species that attempt to use the same limited resource (e.g. hyenas fighting with lions over a carcass or trees competing for sunlight at the top of the canopy)

2.1.7 Interactions should be understood in terms of the influences each species has on the population dynamics of others, and upon the carrying capacity of the others environment.

Predator-prey relationships are often controlled negative feedback mechanisms that control population densities

A population is a collection of individual organisms of the same species that occupy some specific area. The term "population dynamics" refers to how the number of individuals in a population changes over time. Understanding populations dynamics allows for the conservation and management of species. ​

The abundance of environmental resources such as food, water, and space determines how population abundance changes over time. In the presence of unlimited resources, populations grow exponentially. 

As seen to the right, an absence of predation, allows the prey population to increase. As the prey increase in number, food, water, space and other resources becoming limiting causing increased competition and thus reduced survivability among the prey. In addition, an increase in prey allows for the existence of more predators, which in turn will reduce the prey population numbers. Fewer prey, will then trigger increased competition among predators, causing increased mortality in that species. This negative feedback cycle will continue on and on.  

2.1.8 A population is a group of organisms of the same species living in the same area at the same time, and which are capable of interbreeding.

2.1.9 S and J population curves describe a generalized response of populations to a particular set of conditions (abiotic and biotic factors).

In an environment where resources become limited, populations exhibit a pattern of growth called logistic growth. In this case, if one plots the number of individuals in the population over time, one finds a sigmoidal, or S-shaped curve. When population abundance is low, the population grows exponentially. However, as population size increases, resources become limited, the population growth rate slows, and the population abundance curve flattens. The number of individuals present in the population when the growth rate slows to zero is referred to as K, the carrying capacity. The carrying capacity is the theoretical maximum number of individuals that the environment can support.

A "J" curve shows exponential growth. It starts slow the becomes increasingly fast.

2.1.10 Limiting factors will slow population growth as it approaches the carrying capacity of the system

Carrying  capacity is the maximum number of organisms that an area or ecosystem can sustainably support over a long period of time. Limiting factors are factors that limit the distribution or numbers of a particular population. Limiting factors are environmental factors which slow down population growth. Common limiting factors are availability of water, availability of food, environmental temperature, and disease. 

Notice how in the leftmost graph in 2.1.9, the population growth rate (slope of curve) approaches zero as the population approaches its carrying capacity. The reduced growth rate can be attributed to limiting factors. 

Things I Should Be Able to Do

•  Explain population growth curves in terms of numbers and rates

You should be able to identify areas of rapid growth, areas of zero population growth, and areas of negative growth (population reduction). The rate of growth is determined by examining the slope of a population-time graph. The greater the slope, the greater the rate of population growth. 

• Interpret graphical representations or models of factors that affect an organism's niche. Examples include predator prey relationships, competition, and organism abundance over time

For example, considering the graph below, you should be able to explain how both the moose and wolf populations provide feedback to the other population. You should also be able to interpret graphs that depict competitive exclusion. 

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