Lecture 8-Intertidal zone II

Question 1

What was the experiment used to determine the zonation of barnacles (Semibalanus and Chthamalus)?

Answer 1

• transplant experiments
• S. usually lower, C. higher
• so change transplants S. to higher positions, = the S cannot survive as it dessicates (so limited by physical factors)
• why is C. usually higher?
• change C. position, put it lower= cannot survive due to competition with S (S is more fast growing)
• also why is S not in the really deep bits?= transplant there= cannot survive due to predation of a snail that drills in and eats the barnacle out (figured out by cage experiments to keep the snail out and then S. survived well)
• overall the zonation is caused by a variety of factors! -larval settlement patterns of S. and C. explain some of the differences in adult distribution (although settlement overlaps in upper intertidal) -Joe Connell experiments (1961)

Question 2

What is the general distribution of Semibalanus and Chthamalus?

Answer 2

-barnacles occur on both sides of the Atlantic -Semibalanus dominates from the mean high tide level and below -Chthamalus dominates the high intertidal zone -at mean low water level, barnacles are generally rare

Question 3

What is the generalisation that Connell’s experiments have led to about the zonation of intertidal zones?

Answer 3

-the upper limit in the intertidal zone is regulated by physical factors (desiccation etc.), whereas the lower limit is regulated by biological forces (predation etc.) -this has many exceptions e.g. the lower limit of some exposed coast species is determined by wave shock (physical factor)

Question 4

What is the worry with the intertidal zonation patterns and the effect of global climate change?

Answer 4

• that the warming climate will re-organise the outcomes of competitive interactions between organisms in the intertidal zone
• climate change may tip the balance of biological interactions and cause changes in intertidal community structure (hockey stick graph= indicates global warming)

Question 5

What are the environmental conditions at Cape Cod?

Answer 5

• East coast USA
• classical bio-geographic barrier
• colder water to the north and warmer to the south

Question 6

What did the Cape cod experiment mean about the effect of climate change?

Answer 6

-to the south of Cape Cod, Semibalanus and Cthamalus compete= C. dominates the high intertidal zone -to the south S cannot outcompete C in the high intertidal -to the North of Cape Cod, waters are too cold for Cthamalus and Semibalanus occurs right at the top of the high intertidal -the northern limit of Cthamalus is determined by both temperature and competition with Semibalanus -Transplanted Cthamalus moved 80km north of their northern limit survived well when they did not have to compete with Semibalanus -thus C’s competition ability affected by temperature -As land and water temperatures rise, likely to be numerous range extensions of intertidal species and changes in competitive interactions among them

Question 7

How common is competition on rocky shores?

Answer 7

-widespread

Question 8

What is contest competition?

Answer 8

-occurs when some species or individuals of a species defend territories, fight with competitors or have contests that have a winner and a loser

Question 9

What is scramble competition?

Answer 9

-involves all consumers feeding as best as they can

Question 10

What is the example of intraspecific competition among limpets?

Answer 10

• competition for food leads to decreased survival of limpets
• a) survival is greater where there is more food, demonstrating the relationship between competition and the resource
• b) survival is less where numbers of consumers are greater

Question 11

What is a direct species interaction?

Answer 11

-interact directly with one another -e.g. herbivore eats a plant= negative effect on the plant

Question 12

What is an indirect interaction?

Answer 12

-have effect on each other without interacting directly -e.g. predator eats a herbivore, negative effect on herbivore, fewer herbivores is positive for plants so the predator has an indirect positive effect on the plants

Question 13

Can predation modify the dominance achieved by competition and affect species composition?

Answer 13

-yes!

Question 14

What is an example of a community where predation affects the composition of that community?

Answer 14

e.g.- the keystone species Pisaster (the starfish) in the Californian rocky intertidal 1.they live low on the shore and crawl up to consume mussels, whelks and other grazing shellfish 2.Mussels are competitively dominant, occupy almost all space and smother sessile species and exclude other mobile grazers (as they have the byssal threads and can climb on top of things and suffocate them) 3.diversity of animals and plants is reduced when mussels are very abundant 4. the starfish eat the mussels (have external stomach and force the mussels open) and maintains open space and promotes diversity of other organisms through consuming mussels 5.Paine (1974) demonstrated this with a decade long experiment where he removed the starfish= the mussels then colonised almost all of the space and species diversity decreased

Question 15

What is the effect of disturbance on the intertidal zone?

Answer 15

-disturbance in the rocky intertidal is frequent (e.g. storms and other weather events) -large-scale disturbances may lead to unpredictable colonisation, leading to alternate stable states -partly explains why we observe different patches in the intertidal zone with different dominating species despite the predictable outcomes of the processes of competition

Question 16

What is the example demonstrating disturbance effects in the intertidal zone (the brown algae, Morula and barnacles)

Answer 16

-Hormosira banksii (brown alga the one making the Neptune’s necklace), Morula marginalba (drilling carnivorous gastropod), barnacles (get eaten by Morula) -Morula takes cover underneath the wet canopy of Hormosia at low tide (to not desiccate) -barnacle mortality typically high withing and near seaweeds -severe storm in 1974 tore Hormosira away, no cover for Morula so they die -with no predators, barnacles proliferated -rocky intertidal switched from Harmosira to barnacle dominated for 5 years, in some places the effect remains!

Question 17

How does spatial scale affect community composition?

Answer 17

• open habitat patch size due to disturbance affects patch future
• mussels re-colonise small patches by crawling in
• large patches too far to re-colonise ,which allows colonization if patch centre by seaweeds and another species of mussel, which may persist

Question 18

What was the nature experiment at Cape Cod?

Answer 18

-they built a waterway= mixing the warm and cold water, opening a way through -then the distribution of C. observed and get halfway through the waterway to the North and then absent (where colder water) -barnacles Cthamalus prefers warmer water (in the south) and lives in high intertidal -transplant experiment, put C. into the colder water further north and survival was good as long as Semibalanus was not there! so it is not the temperature but competition that affected its distribution