Biosphere

Population

  • is the number of organisms of the same species that live in a particular geographic area at the same time, with the capability of interbreeding.

  • For interbreeding to occur, individuals must be able to mate with any other member of a population and produce fertile offspring.

  • Population biology - is the study of population characteristics and the factors that affect their size and distribution.


Factors Governing Population Size:

  • Birth Rate - The birth rate is the ratio between the number of live-born births in the year and the average total population of that year.

  • Immigration - means to move into a non-native country or region to live.

  • Death  Rates (Mortality Rate) - a measure of the number of deaths (in general, or due to a specific cause) in a particular population, scaled to the size of that population, per unit of time.

  • Emigration - means to leave one location, such as one's native country or region, to live in another.

  • The human population is projected to reach 7.7 billion people by the year 2020.


DYNAMICS OF HUMAN POPULATION 

  •  Before 2000, the population had a high mortality rate because rural/urban areas have low medical equipment and facilities and the distance is far.

DEMOGRAPHIC TRANSITION 

  • Because death rates fall before birth rates, population growth initially speeds up (a phase sometimes referred to as the mortality transition)

LIFE EXPECTANCY 

  • Due to advanced and updated medical facilities and rapid food consumption and distribution. The life expectancy rate thus increasing in both (more and less developed) regions.

Overpopulation - the state whereby the human population rises to an extent exceeding the carrying capacity of the ecological setting. 


TYPES OF SPECIES INTERACTION 

  • COMPETITION 

  • PREDATION 

  • SYMBIOSIS 

  • PARASITISM 

  • MUTUALISM 

  • COMMENSALISM 

  • COMMUNITY STRUCTURE 

  • SUCCESSION


Adaptation

Adaptation is used in two ways:

  • Individual (moving from one place to another)

  • Population (evolution)

NATURAL SELECTION

  • Members of a population best suited for a particular set of environmental conditions survive and produce offspring more successfully than their competitors. 

  • Acts on pre-existing genetic diversity. 

  • Limited resources place selective pressures on a population.

SPECIATION 

  • Given enough geographical isolation or selective pressure, members of a population become so different from their ancestors that they may be considered an entirely new species. 

  • Alternatively, isolation of population subsets, preventing genetic exchange, can result in branching off of new species that coexist with the parental line.

ECOLOGICAL NICHE

  • Ecological Niche is a Role that species plays in a biological community (e.g. large grassland herbivore).


 Habitat - Place or set of environmental conditions where a particular organism lives.  


Total set of environmental factors that determines a species’ distribution

  • Generalists - Broad niche 

  • Specialists - Narrow niche 


  • When generalists and specialists collide, generalists usually win.

  • NICHE FACTS - The role of species in an ecosystem. 

- Niches can vary in size. 

-If niches overlap it may cause competition.


  • NICHE DIFFERENTIATION DESCRIBES THE WAY BY WHICH COMPETING SPECIES USE THE ENVIRONMENT DIFFERENTLY IN ORDER TO EXIST.

  • Competitive exclusion - One species will use the resources more efficiently and drive the other species to local extinction.

  • Resource partitioning - Two species will alter their use of the niche to avoid direct competition, allowing for co-existence.

LAW OF COMPETITIVE EXCLUSION 

  •  No two species will occupy the same niche and compete for exactly the same resources for an extended period of time. 

  • One will either migrate, become extinct, or partition the resource and utilize a subset of the same resource. 

  • Given resource can only be partitioned a finite number of times.

PREDATION 

  • Feeds directly upon another living organism, whether or not it kills the prey in doing so.

  • Prey most successfully on slowest, weakest, least fit members of target population. 

  • Reduce competition, population overgrowth, and stimulate natural selection. 

  • Co-evolution (arms race).

SYMBIOSIS 

  • Both members benefit.


MUTUALISM

  • Intimate living together of members of two or more species.

COMMENSALISM 

  • One member benefits while other is neither benefited nor harmed. 

PARASITISM 

  • When one organism feeds on usually live or in another species.


BIODIVERSITY 

3 types of biodiversity:

  • Genetic Biodiversity – is the total number of genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within species and can be attributed to the span of survival for a species.  

  • Species Biodiversity – is defined as the number of different species present in an ecosystem and relative abundance of each of those species. 

  •  Ecosystem Biodiversity - can be defined as the variety of different habitats, communities and ecological processes.

THREATS TO BIODIVERSITY 

  • Habitat Destruction - Important to protect habitat in order to protect biodiversity within it. Huge pressure from the World’s rapidly increasing population. 

  • Global Climate Change - Change in a biotic elements of ecosystems leading to biotic change. 

  • Habitat Fragmentation - From human activity. Reduces ability of habitat to support species. 

  • Pollution - Introduction of pollutants such as nutrient overloading with nitrate fertilizer as well as more immediately harmful chemicals. 

  • Over-Exploitation - This includes the illegal wildlife trade as well as overfishing, logging of tropical hardwoods etc. 

  • Alien Species - Introduced by humans to regions where there are no natural predators. 

  • Disease - Reduction in habitat causing high population densities, encourages spread of diseases.


ABUNDANCE AND DIVERSITY 

Abundance -Total number of organisms in a community. Diversity - Number of different species, ecological niches, or genetic variation. 


PRODUCTIVITY

Primary Productivity - Rate of biomass production. Rate of solar energy conversion to chemical energy. 

Net Primary Productivity - Energy left after metabolism 


COMMUNITIES IN TRANSITION ECOLOGICAL SUCCESSION 

Primary Succession - A community begins to develop on a site previously unoccupied by living organisms. 


  • Ecological Development - Process of environmental modification (facilitation) by organisms. 

  • Climax Community - Community that develops and seemingly resists further change. 

  • Equilibrium Communities (Disclimax Communities) - Never reach stable climax because they are adapted to periodic disruption.


Secondary Succession - An existing community is disrupted and a new one subsequently develops at the site.