predator - prey interactions

Nota:

• there are 5 types of predation  herbivory  carnivory  insect paranoids - laying eggs  parasites  canibilism ie life cycles eating juveniles 

1. rocky shore exsamples

   Nota:

   • prey are slow moving and sessile and have developed hard shells as protection  due to coevolving the predators are slow and concentrate most of their energy into breaking down walls also no need to move quick if prey doesnt 
   1. dogwhelks

      Nota:

      • these are some of the most common predators on the shore  they inject digestive enzymes and acid onto the shells to break them down from the inside 
      • this can take upto weeks, therefore the greatest challenge is deciding wether the calorific vakue is worth the effort to digest  see palmar 1990a 
   2. crabs

      Nota:

      • are known for there broad diets however in europe its mostly dogwhelks and mussels 
      • prey item varies from clumped to single organisms 
      • they use thier claw to crack open shells and damage prey depending on the prey size 
      • littorinds dont need to be smashed and those on sheltered shores are better and preventing predation 
      • however on exposed shores crabs have less time to find the best prey item before being dislogded, so they are more opotunist predators 
   3. Nudibranchs

      Nota:

      • they are grazers using thier teethed radula to scrape algae and prey, they are very messy eaters an kill more then they actually consume 
      • they are very specific with which prey they eat, certain species only eat certian prey which can cause high competition with other species 
   4. predatory fish

      Nota:

      • they can be split into four catagories  -residents -partial residents  -tidal  - seasonal 
      • many of them over come the fortress stregie by being nig enough to eat whole organisms - sea bass  they are very territorial 
      • some have different food per life stage such as gobbies and barancles the juveniles only eat the cillia where as the adults eat the whole thing 

1. dog whelk

   Nota:

   • dog whelks are constrianed by the weather, high wave action or high chances of dessication mean that they have very limited time to move 
   • meaning that in bad conditions it will feed on any prey item it find until being selective in optimal conditions 
2. crab

   Nota:

   • many predators forage to stick to thier energy budget.  basically get the maximum energy back that they can 
   • carcinus mainus uses chemical signals in the water to taste where and how fair thier prey is 
   1. approach to mussels

      Nota:

      • crabs pick up the mussel and for 2 to 3 seconds minipulate it, see if its worth the effort then they try and crack it with one movement  the bigger the mussel the more energy is needed to open them 
      • elner and hughes 1978  showd that mussels of intermediate size were much better value for energy budget 
   2. approach to dogwhelks

      Nota:

      • due to dogwhelks not being so numerous its more down to if the shell can be open between 0.25-2.75 seconds - smaller ones can be crushed easily where as the larger ones are opened by gaps and damages 

Nota:

• predation stargies can be shown to influence population and morphology such as dogwhelks and their shells on exposed shores are thinner and wide this is due to less time out on the shore predation so dont need that extra protection 

1. Morphology

   Nota:

   • as mention by dogwhelks their shell is dictated by their environment and their foraging sucess as exposed shore whelks suffer more damage from crabs 
   • teeth and shell can be dictated by predators as shown by palmar 1990b  they showed that diffrent teeth grew due to different chemicals and prey present 
2. Density and distribution

   Nota:

   • changes in predator populations can have big effects on the prey as shown by dogwhelks 
   • removing the whelks has increased the amount of barnacles and mussels present on the shore 
   • as shown in australia - removal caused changes in prey in different levels = patichness  semibalanus is said to be effected in the midshore by predation 
   • however these are complicated and predation hardly ever acts only  ie dogwhelks in uk shores - menge 1976 however its not the only predator present - so there are other facotrs 

1. littorina littoria

   Nota:

   • they use a clamp down method where as if they see a predator they stomp and dislogd the predator 
2. littorina saxatilis

   Nota:

   • shell shape 
3. fabilis

   Nota:

   • colour morphs - whcih provide protection within the fucus plants 
4. urchins

   Nota:

   • urchins hide themselves in the day when thier predator is foraging and hide in wholes so they take them selves out of site from the predator 

1. might change distribution and effect number of prey
2. predation and competition organise a communty struture
3. major adaptive force
4. many predator prey relationships last over generation with overlap and they are shown by graphical equations

   Nota:

   • see lecture slides for details on the graphs, however the graphs make alot of asumptions  ratio is therefore used to make the graphs more realistic