Plant responses to the biotic environment

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Plant responses to the biotic environment
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• The resources that are important for plants are
  light, water, minerals, oxygen, carbon dioxide
  and space. Plants also need to defend themselves
  against herbivores.

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Plant-plant relationships

• Many plants secrete a poisonous substance into
  the soil to prevent other plants growing near
  them allelopathy.
• Seed dispersal means spread over a wide area to
  ensure survival.
• Plants in reduced light grow larger leaves

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• Stratification means plants are adapted to
  different light intensities to grow in different
  conditions.
• Epiphytes are plants that perch on tall trees to
  get light at higher intensities. Lianas are
  plants that climb tall trees for the same reason.
• Plant parasites true suck the sap and do not
  photosynthesise, hemi-parasites suck the water
  but do own photosynthesis.

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• Seaweeds are adapted to different depths green
  at surface, brown mid depth and red deepest.
• Cluster growing different species grow close
  together to support each other (mainly grasses).
• Fruit trees rely on others to pollinate (pears,
  feijoas)
• Clover benefits other plants growing near due to
  the bacteria in their roots.

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Plant-fungi relationships

• Mycorrhizal fungi forms mutulistic relationships
  with many plant roots. Very important in pine
  forests in NZ. They help plants absorb water and
  get nutrients in return.
• A lichen is an obligate mutulistic relationship.
  It is an algae and a fungi that have to live
  together to survive.

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Plant-animal relationship

• Herbivores eat plants in many ways graze,
  browse, sapsuckers, nectar feeders, stem borers,
  chewers, pollen feeders, fruit eaters, seed
  eaters, gum eaters.
• Plant defences against herbivores
• Thorns modified side branches, spines modified
  leaves and stings which are modified hairs.
• Divarication plants that branch at wide angles
  with closely interlaced branches.

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• Chemicals toxic or just bad tasting, some plants
  produce antibiotics when attacked (caffeine,
  chilli), chemicals produced when chewed (cyanide,
  pyrethins, tannins, nicotine, strychnine etc., or
  smells released to stop animals landing on them
  (onion, garlic etc).
• Sticky sap or seeds to trap would be eaters
• Low growing point to recover quickly
• Enclosing seeds in hard shell or prickles
• Seed masting
• Hiding
• Regeneration
• Waxy cuticle and epidermis

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Co-operative relationships between plants

• The presence of one species of plant growing near
  another may protect it from grazers marigold
  roots secrete a nematode killing chemical that
  helps other plants nearby, willows and alders can
  communicate by airborne chemical cues to develop
  insect resistant chemicals.

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Co-operative relationships between plant and
animals

• Pollination
• Ant guarding
• Living among thorns
• Eating succulent fruit