p3

how can phosphate be lost from agricultural land?

• leaching

• run off

• removed by harvesting of agricultural crops

effects of changes in world rock phosphate production.

• phosphorus is important as a fertilizer

• a drop in phosphate could lead to less agricultural output

• less food available for increasing population

gersmehl diagram

models nutrient stores and flow in an ecosystem

competitive exclusion

• two species that occupy a similar niche in the same location cannot coexist

• one of the two competitors will always have an advantage over the other

• leads to extinction/displacement/evolution of the second competitor

• the niche of one or both competitors becomes narrower

keystone species

they have a disproportionate effect on the biological community (removal of one, leads to more the one below, leading to a reduction of the one below the second)

capture-mark-release

• a species is captured and marked

• release back into the ecosystem and allowed to mix

• a second sample is captured

• sufficient time given between the first and second capture to let them mix

• area of habitat determined

• assumes there is no emigration/immigration/death of snails

• assumes the marking of the snails doesn’t affect their survival

• assumes there is no misidentification of species

• assumes marked species do not lose their markings

invasive species

overlap with native species’ niches

indicator species

• need particular environmental conditions

• change in population over time shows effect of environmental conditions

• used to calculate biotic index

• high index number (10) indicates totally unpolluted

exponential growth phase

• ideal environment/unlimited resources/below carrying capacity

• little disease/few predators

• high natality rate and immigration, greater than mortality and emigration

carrying capacity

• maximum population size that an environment can support

• population growth fluctuates as the carrying capacity is reached

example of captive breeding

• Giant panda

• endangered due to loss of habitat/hunting for fur

• bred in zoos/ex situ/China

• programme was carried out by breading/raising in captivity

• relative success re-introducing to the wild

use of fertilisers on crops and their effect on other ecosystems

• adding fertiliser increases nitrogen/ phosphate in soil

• adding fertiliser increases crop yield

• commercial fertilisers may release compounds more rapidly but not stay in the soil for as long as organic fertilisers

• nutrients run off into water

• high concentrations of nitrogen/phosphate causes eutrophication and algae to multiply rapidly

• algae die and are decomposed by bacteria

• bacteria require oxygen from water (high BOD)

• if oxygen levels drop too low, aquatic organisms die

evaluate the methods used to estimate populations of marine organisms

• sampling does not count every organism so it may not be a true estimate

• highly mobile marine organisms are unevenly distributed so difficult to estimate

• quadrants used to calculate stationary organisms

• useful on rocky shores, beaches

• capture-mark-release for mobile organisms in restricted environments

• fish maybe estimated this way

• echolocation to estimate fish populations

• echolocation cannot distinguish between species

discuss how crop plants obtain the phosphorus that they need to grow and whether the supply of phosphorus to crops is sustainable

• plants absorb phosphorus from the soil by the roots

• soil phosphorus comes from weathered rocks

• phosphorus is a limiting factor in plant growth

• phosphorus cycle is too slow

• it is replenished by fertilisers

• mined from rocks

• rocks are non-sustainable

• increased demand for food increases demand for fertilisers

• runoff of fertilisers decreases potential supply for crops