populations Flashcards
What is a population growth
curve?
The same characteristics sown by
the growth of most natural
populations
What are the phases in a
population growth curve?
Phase 1 • Slow growth • Small numbers of individuals initially present reproduce, increasing total population • Birth rate higher than death rate, so population increases in size Phase 2 • Rapid growth • Number of breeding individuals increase so the total population multiplies exponentially • No constraints act to limit the population explosion Phase 3 • Stable stake • Further population growth is prevented by extreme constraints • Population size fluctuate but overall size remains relatively stable • Birth rates and death rates are approximately equal - fluctuation as due to fluctuations in limiting factors
What is a limiting factor?
The factor whose magnitude slows down the rate of a natural process • e.g. Competition for resources, build-up of toxic by-products of metabolism, disease
How are limiting factors
categorised?
• Abiotic factors: temperature, light, pH, water and oxygen availability, and humidity • Biotic factors: predators, disease, competition
What is carrying capacity?
The maximum population size that
can be maintained over a period in a
particular habitat
What are the two types of
strategist?
r-Strategists and k-Strategists
Describe k-Strategists
Species whose population size is determined by the carrying capacity The limiting factors have a more significant effect as the population size gets closer to the carrying capacity e.g. birds, larger mammals, larger plants
What are the characteristics of
k-Strategists?
- Low reproductive rate
- Slow development
- Later reproductive age
- Long lifespan
- Large body mass
Describe r-Strategists
Species in which the population size increases quickly and can exceed the carrying capacity of the habitat before the limiting factors start to have an effect aka ‘boom and bust’ population growth e.g. mice, insects, spiders, weeds
What are the characteristics of
r-Strategists?
- High reproductive rate
- Quick development
- Young reproductive age
- Short life span
- Small body mass
What are the steps in the
predator prey cycle?
1. As the predator population gets larger, more prey are eaten 2. The prey population decreases, leaving less food for the predators 3. With less food, fewer predators can survive and so their population size decreases 4. With less predators, fewer prey are eaten and so their population size increases 5. With more prey, the predator population increases, and the cycle begins again
When does competition
happen?
When resources e.g. food or water are not adequate to satisfy all of the individuals that depend on the resource • Intraspecific and interspecific competition
What is intraspecific
competition?
Competition between individuals of the same species The individuals best adapted to obtaining the resources survive and reproduce, whilst the others die
What is interspecific
competition?
Competition between individuals of different species The more overlap between two species’ niches results in more intense competition, and if one species is out-competed, it could die out or become extinct in that habitat
What is preservation?
Maintenance of habitats and
ecosystem in their present
condition, minimising human impact
What is conservation?
Maintenance of biodiversity, including diversity between species, genetic diversity within species, and maintenance of a variety habitats and ecosystems
Give 3 threats to biodiversity
• Over-exploitation of wild population for food or commerce • Habitat disruption and fragmentation due to agricultural practices • Species being introduced to a new ecosystem by humans, and then out-competing other native species
Give examples of conservation
practices
• Raise carrying capacity by providing extra food • Moving individuals or encouraging natural dispersion of individuals to fragmented habitats • Restricting dispersal of individuals by fencing • Controlling predators and poachers • Vaccination against diseases
What are the ethical reasons
for conservation?
Every species has value and
humans have an ethical
responsibility to look after them
What are the economic and
social reasons for
conservation?
• Many plant and animal species provide a valuable food source • Genetic diversity may be needed in the future to breed diseaseresistant species • Many drugs are discovered in wild plant species • Natural predators of pests can act as biological control agents • Pollination • Ecotourism and recreation in the countryside
How can small-scale timber
production be sustainably
managed?
Rotational coppicing The woodland is divided in sections and only 1 section is cut each year, leaving the rest unmanaged and allowing it to go through a process of succession
How can large-scale timber
production be managed
sustainably?
• Replacing harvested trees by planting new ones • Controlling pests and pathogens • Only planting particular tree species where they are known to grow well • Positioning trees an optimal distance apart
How are fish stocks
sustainably managed?
• Fishing must take place at a level that allows it to continue indefinitely (i.e. no over-fishing) • Fishing must be managed to maintain the structure, productivity, function and diversity of the ecosystem • International regulations
Give an example of where the
conflict between conservation
and human needs is balancing
Terai region in south Nepal • Densely populated and home to endangered species e.g. the Bengal tiger • The forests have been under pressure from expansion of agriculture and grazing of farm animals • The forests are home to many endangered species but also provide local people with fuel, animal feed, food, building materials, agriculture and medicines To ensure conservation, the WWF introduced community forestry initiatives with local people where they had the rights to exploit the forest as well as responsibilities to look after it • Construction of water holes • Monitoring endangered species • Eradicating invasive species • Creation of forest corridors
