Populations and sustainability

Question 1

what is carrying capacity? what kinds of habitats have high/low carrying capacities?

Answer 1

the maximum population size that the environment can sustain. Tropical rainforests have high carrying capacities due to plentifukl factors for photosynthesis and plant growth, deserts have much lower carrying capacities

Question 2

what will usually happen if a population exceeds the habitat’s carrying capacity for a short time? list limiting factors

Answer 2

population size will decrease due to limiting factors which stop a population from increasing any further e.g: amount of food, space, predators, diseases, parasites, temp., light intensity/CO2/temp for plants

Question 3

how does the amount of food/nutrients/mineral ions in a habitat act as a limiting factor to population size?

Answer 3

used up faster by a large population - scarce food results in weaker individuals that are more susceptible to diseases and predation so population size decreases

Question 4

how does the amount of space in a habitat act as a limiting factor to population size?

Answer 4

e.g. nesting sites for birds, territories for foxes - without suitable breeding sites some individuals may not be able to reproduce

Question 5

how does the amount of predators in a habitat act as a limiting factor to population size?

Answer 5

a larger population is mroe vulnerable to predators as some individuals will be weaker due to lack of food and more young are likely to be taken by predators

Question 6

how do diseases act as a limiting factor to population size?

Answer 6

are spread more easily in over crowded conditions, especially when some individuals e.g. young are weaker. Parasites are also more easily transmitted in large populations.

Question 7

how does temperature (animals) act as a limiting factor to population size?

Answer 7

some animals such as fish cannot regulate their body temperature. Growth rates of these individuals are dependent on the external temperature and populations grow more slowly in cold climates

Question 8

how does light intensity/CO2 conc/temp (plants) act as a limiting factor to population size?

Answer 8

are all factors affecting rate of photosynthesis - less photosynthesis = less energy = slower growth rate of populations

Question 9

describe a typical graph showing predator- prey relationship

Answer 9

mirrors - ondulates with a time lag between peaks:
Increased numbers of prey = more food for predators and increases chances of predation especially if prey are weakened due to competition for food.
This causes an increase in no. of predators as more of their offspring survive and reproduce.
inreased no. of predators = decrease no. of prey as mpre are eaten
decreased prey = decreased predators eventually as less food available and more interspecific competition.
Decreased predators = more prey survives and reproduces so numbers increase.
etc.

Question 10

describe intraspecific competition

Answer 10

competition for limited resources between members of the same species because they occupy the same ecological niche, and have similar morphological, physiological and behavioural features.

Question 11

describe interspecific competition

how can it be reduced?

Answer 11

between two different species relying on the same food source or having other similar requirements/niches in the environment.
Important in determining the distribution and population sizes of species in habitats, and can be reduced if species are found in different parts of the habitat or are active at different times.

Question 12

What is the main difference between conservation and preservation?

Answer 12

preservation means keeping things the same whereas conservation aims to maintain or increase biodiversity in ecosystems and to increase population numbers of rare/endangered species. Conservation is a dynamic process involving active management and reclamation of habitats

Question 13

How can woodlands/forests be managed to allow timer production each year without destroying the ecosystem?

Answer 13

Coppicing allows species diversity to be maintained or even increased as ,pore light reaches the ground in newly coppiced areas so more ground-cover plants can grow.

Question 14

why is the selective cutting of large trees better than clear felling in a habitat? (4)

Answer 14

• less disturbance to the habitat
• less reduction in species diversity
• tree roots remain to bind the soil
• prevents soil erosion by rain or wind

Question 15

outline some economic reasons for conservation

Answer 15

• resources can be used indefinitely in sustainable e.g. timber from coppiced woods
• maintenance of biodiversity important for discovery of medical drugs, to allow selective breeding in the future, animals conserved as food sources…
• predators and parasites of pests can be used as a cheaper form of biological control than chemical pesticides
• species diversity is important for tourisms e.g. on the Galapagos islands

Question 16

outline some social reasons for conservation

Answer 16

• many people benefit psychologically from time spent in natural habitats - reduces stress
• communities dependent on fishing/ecotourism can be disrupted
• management of ecosystems can provide jobs
• aesthetic/recreational value
• to stop effect of deforestation on atmosphere / climate / soil

Question 17

outline some ethical reasons for conservation

Answer 17

• all species have a right to survive
• human responsibility to look after other species
• humans should be able to coexist with other species and not destroy habitats

Question 18

outline 3 effects of human activities on the populations in the Galapagos islands with examples.

Answer 18

1. habitat disturbance: increased population size (5000 in 1980 to 28000 in 2005) has resulted in loss of habitats for housing, roads and agriculture. More pollution/waste/oil spills toxic to wildlife.
2. Over-exploitation of resources: whales, seals, giant tortoises hunted and killed for food oil and fur, faster than the populations could recover by reproducing. Over-fishing of exotic fish species, disrupting marine food-webs.
   3, Introduced species: Goats, cats, fruit and veg plants introduced deliberately, insects and other species introduced accidentally. Alien species out-compete native species, eat them, bring diseases, destroy habitats.e.g. goats out-compete giant tortoises for purslane and trample their nests sites. They also destroy forests leading to soil erosion.