With this post I join the third Biology carnival, hosted this time by Pakozoico . The theme of this edition are trophic relationships, so I go there with an example of how human influence can load an entire ecosystem, through trophic relationships.
The example of the cascade effect that I want to show takes place in the North Pacific, particularly in kelp forests that exist or should exist in the shallow bottoms and illuminated American Pacific coast north .
The kelps are brown algae of the Laminariales order, comprising several families that contain, among others, gender Nereocystis and Macrocystis present on the coast North American Pacific. In shallow water, low-temperature form what is known as "kelp forest" and growing at up to half a meter a day, reaching heights of several tens of meters. Due to its large size provide a structural framework to develop a complete ecosystem around: epiphytic species growing on its surface, algae with lower light requirements, or parasitic algae, grow in their shade; marine invertebrates like sea urchins, starfish and various species of herbivorous gastropods feed on kelp and other associated algae and filter feeding shellfish and other animals find their food detritus in waters nutritious kelp forests provide. Several vertebrate species also exploit the many advantages of living in a neighborhood with kelp present: fish like cod alaska ( Ophiodon elongatus) or a species of redfish (Sebastes borealis ) are residents, while migratory species, including 5 species of Pacific salmon and herring, can usually find in these ecosystems. Even different species of marine mammals benefit from the advantages of kelp forests, and sea otters (Enhydra lutris), and some species of seal or sea lion, resident, or the gray whale migration ( Eschrichtius robustus), which uses kelp forests and breeding grounds yearly.
far so good, great diversity of species Convivienda love and companionship or forming a food web that could look a lot like this one here:
You can see the otters are solitary in top of the scheme. That basically means that are higher level predators of the ecosystem, no one eats, go (except some occasional shark.) That also means, and here comes the interesting part, that otters are a keystone species (keystone species in English) in this ecosystem, as control through predation, the abundance concerning the various invertebrates that are part of your diet and, to summarize, if we take the otters of the scheme, " the liam brown." Before the otter is the subject of commercial whaling, there were people in the intertidal zone around the North Pacific from northern Japan and the "Kuril Islands" through the Aleutian Islands and the entire west coast of North America to Mexico. The population then was estimated at between 150,000 and 300,000 individuals. But the white man arrived. And with him on commercial whaling. Otters are the only marine mammals that do not have with a thick layer of fat to maintain their body heat, and compensate for this deficiency with a very thick and dense hair. Apparently, one square inch of skin (yes, American measures, is what it is ...) contains 1 million hairs, which according the web where I found the data is more we have in the whole head.
This hair became very popular for ladies clothing and ladies of high society from the XVIII S, and otters were hunted for 170 years, until in 1911 he signed "Fur Seal Agreement" and hunting stopped. By then, however, the damage was done and there were only about 1,000 or 2,000. Under the new treaty protecting the population of otters was recovering slowly, reaching the 150,000 individuals again, although in some areas of historical distribution never recovered, and otters are now extinct in certain areas.
Let's talk about the sea urchins. It is one of several species of invertebrate herbivores that live in the shadow of kelp are, in fact, ill children should monitor the otters, the reason why these are so important: sea urchins are a tireless dining. If nothing stops them, walked along the rocky bottom eating all the plant material is placed in its path and leaving behind what is known in Spain as "barren" (term notorious for canaries diving enthusiasts) and English as "urchin barrens" . In areas that have been destroyed in this way for the hedgehogs, the food web looks very different to that seen so far: the large algae disappear, sea urchins feed on algae blooms and rapid growth of algal remains derived production primary therefore plummet, and there is no primary production herbivores, carnivores, therefore there is therefore no debris, hence no nutrients, no nothing. The only animals that survive these conditions are austere urchins themselves, thus leaving a food web that may seem pretty well to this:
The intimate relationship between the presence of otters and health forests of kelp (urchins by) was studied and recognized by the otter reintroduction projects to be conducted off the coast of Vancouver (Dr. Jane Watson at the beginning of the 90) and Alaska and the Aleutian Islands (Estes and Duggins, 1995) after the treaty was signed guard.
A new actor enters the scene towards the end of the twentieth century: the killer whale (Orcinus orca ). Since 1991 Dr. James Estes, host of previous studies on the relationship between sea otters, sea urchins and kelp, has been observed killer whale attacks on otters, a phenomenon that has not been reported before. The main hypothesis is that overfishing in the North Pacific and Bering Strait would have reduced the amount of food available to common seals ( Phoca vitulina) and Steller sea lions ( Eumetopias jubatus) , usual prey of orcas. This, in turn, would make these stocks fall, forcing the whales to find other snacks to those who supplement their diet. Apparently found in otters. To confirm this hypothesis, the researchers conducted studies in two different areas: in one, "Clam Lagoon, protected from access by orcas, the otter population was stable for the duration of the study, from 1993 to 1997, while in the next bay of "Kuku Bay, easily accessible for cetaceans, the otter population declined by 76% (! ). Other possible causes for the decline in the number of otters, as could be diseases, toxins or lack of food were gradually discarded, until the only logical explanation was predation by killer whales. To add drama to the situation, as we have said, the otters have no layer of fat (blubber) to protect marine mammals from the cold, and how tempting it seems to orcas. For this reason a food are much less energy, so that a whale should Otters eat about 1,825 per year to meet your needs. Made the necessary calculations, this means that only four whales feeding exclusively on sea otters could be responsible for the decline of the otter population experienced much of the Aleutian Islands.
As if this were not enough, this chain reaction is also affecting the animal emblem of the United States of America ( Ooh say, can you see, Naina Naino naaaniaaa ) the bald eagles (Haliaeetus leucocephalus ). Apparently these animals were among the many kelp forests used as a hunting ground. Bald eagles and ospreys Americans get the vast majority of their food from sea, land and coastal environment that offers little chance of prey for them. In the presence of kelp forests feed on fish living in them, and otter pups. When kelp forests disappear, just looking for other species of fish or seabirds at sea that they could serve food. And apparently have not fared as badly as some studies show that in populations where there has been this change of diet females produce more offspring, the researchers believe this may be due to seabirds provide more calorific food otter pups, bringing more energy. Although a priori this is good, we can not foresee the implications on ecosystems and food webs in which the bald eagle is involved, this increase in the population of this predator. It should also be borne in mind that many other seabirds that used kelp forests to find food may have more difficulty in getting an alternative diet, producing so many imbalances in many other food webs ... The end is the never ending story, and it is dangerous to start playing ...
The Otters have relationship with the kelp by urchins is what is known as a trophic cascade , or top-down regulation : a progression of indirect effects of predators across successively lower trophic levels. Or what is the same, the presence or absence of otters has indirect effect on the survival of kelp forests through the control they exert over the sea urchins to eat. If you also come into play man, either by removing the otters of the system by direct hunting or removing food from the main prey of killer whales (sea lions and seals) and forcing them to eat otters, imbalance results may take dozens and dozens of years to clear, if it ever does, and can have ramifications that now fail to see or imagine.
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