Amongst the plants there were two species of grasses. Scientists assume that most of these plants arrived via wind, but some species could have arrived as seeds carried by the surf. Further colonization of the barren island then began to accelerate. By , young trees were found as well as dense grassland and many ferns. Butterflies, beetles, flies and a single monitor lizard were found in By , there were a hundred species of vascular plants, covering the summit in green and a grove of trees along the shore , including tamarisk and coconut palm. The coconut is found on virtually any sunny beach in the Pacific because its seeds float in their large protective shell wherever the current carries them.
Fifty years after the eruptions of , the island was home to species of plants. These early arrivals were effective dispersers, but they also had to be capable of surviving inhospitable conditions on arrival.
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The order of arrival is therefore an important factor in determining successful establishment. The many projects all over the Bay Area that destroy non-native vegetation are not isolated islands. They are surrounded by more non-native vegetation which quickly re-populates the bare ground created by these projects. Dispersal into small plots of land within San Francisco is much easier than onto isolated Krakatoa. The majority of these projects do not have the resources to replant the areas in which non-native vegetation is eradicated.
The fiction is that native plants will magically reappear when non-natives are destroyed. But we can see that the result is the return of the hardiest non-native weeds such as hemlock, star thistle, oxalis, and broom. Their seeds are carried by the wind or remain dormant in the ground to germinate when someone foolishly destroys the trees that provide shade and suppress germination of weeds. Even when natives are planted, they are quickly out-competed by non-natives.
The best local example of that hard, cold fact is the living roof on the California Academic of Sciences. Thirty species of native plants were candidates for planting on the roof.
They were planted in test plots with conditions similar to the planned roof and monitored closely. The monitoring project divided the roof into four quadrants. In February , non-natives outnumbered natives in two of the quadrants. Although natives outnumbered non-natives in the other two quadrants, non-natives were also growing in these quadrants.
The consultant who advised the Academy about what to plant on the roof would not be surprised by this monitoring report. He advised the Academy to walk the streets of San Francisco and identify the plants growing from the cracks in the sidewalks. These are the plants he advised the academy to plant because these are the plants that are adapted to current conditions in the city. The Academy rejected this advice because they were committed to planting exclusively natives on the roof. The many projects that are destroying non-native vegetation are not sustainable. They are surrounded by non-native vegetation which is better adapted to current climate, soil, and atmospheric conditions.
Non-native vegetation will out-compete the natives that are not adapted to current conditions. If these projects were merely futile, perhaps we could shrug and move on. They use huge quantities of toxic herbicide and they are destroying healthy trees that are performing many valuable ecological functions. These are not harmless experiments. Very, very good analysis and post.
Though long, I read every word. It is not too difficult for learned people to see the errors of this movement. How many bees do we lose? Pesticides stay in the soils and bees ingest it through the nectar they drink and pollen they collect. And pesticides are used in clearing non-natives most efficiently. In: Tuatara: Volume 23, Issue 2, July Publication details: Wellington. Part of: Tuatara : Journal of the Biological Society. Conditions of use. Biogeography is the study of the distribution of organisms upon the surface of the globe.
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Biogeography is often divided into phytogeography plants and zoogeography animals but as the problems both face are essentially the same the division is not recognised in this paper. See Croizat, ; Fleming, , and Banarescu, , for further discussion of this. Darwin believed that species originated in centres from which they dispersed by either passive or active dispersal mechanisms:. Darwin's biogeographic concepts were expanded and elaborated by a number of subsequent authors in books and papers which have had a significant impact on the development of biogeography.
The fundamental assumptions underlying all Darwinian biogeography as noted by Croizat a: are. Since it is normal to find that plants and animals lacking said means are very widely distributed the conclusion is normally reached by orthodox — so called — phytogeographers and zoogeographers that means of dispersal are essentially mysterious.
The centres of origin concept was challenged as early as Croizat et al. Cain demonstrated that none of the 13 criteria advanced for recognition of a centre of origin were of any real value in biogeographic studies. Vicariance biogeography basically conceives of present day biotic patterns as having arisen from the fragmentation of ancestral biotas due to geological and geographical change.
Croizat's work finds its immediate historical roots not only in the work of Cain but also in Rosa's theory of hologenesis i. Biogeographical implications of hologenesis are that:. Without denying migrations, hologenesis ought to make as a basic principle of biogeography not a distribution arising from different centers, but a primitive cosmopolitanism succeeded by a process of localisation taking place at the same time as the multiplication and differentiation of species.
Whether the Bay of Bengal came about because the Deccan and the Indo-Chinese Peninsula, respectively, did drift apart, or whether land once in between its current shores crumbled, is not a question to interest the student of dispersal very deeply. The student takes stock of the page 84 records of the geographic distribution of plants and animals, and objectively analyses them on a comparative basis, drawing the conclusions which the facts advise and common sense endorses.
One of the major problems in biogeography is finding an explanation for the faunal and floral resemblances between widely separated tropical and Southern Hemisphere temperate regions. Darwin believed that cold, glacial periods drove organisms from areas around the north and south poles into equatorial regions where they mingled together. When climatic conditions improved northern organisms were able to migrate southwards with the southern organisms; but southern organisms were unable to migrate into the Northern Hemisphere.
Similarities between, and the presence of related organisms, in two or more of the Southern Hemisphere land areas was attributed to long-distance dispersal across water gaps. From here animals migrated into South America, while they also migrated from Eurasia into Africa and along the Indonesian chain of islands into the Australasian region. Wallace adhered generally to a permanence of continental areas but was prepared to accept ancient land connections with regard to New Zealand and the Celebes which he class as anomalous islands.
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Matthew developed these ideas even further. According to Matthew the main groups of vertebrates arose in centres of origin in northern parts of the Holarctic and dispersed southwards along the three independent routes mentioned above. He believed that 1 animals disperse from large areas, into small areas, of land; based on the assumption that animals tend to disperse from continents to islands and not vice-versa, and 2 Matthew considered that alternations of arid and cold climatic zones in Holarctica resulted in the page 85 evolution of more competitive forms of life, i.
Because he believed in the permanence of continents and oceans the fact that there is more land in the Northern Hemisphere meant that animals dispersed from these regions into the smaller southern areas. New and more progressive animal forms evolved in northern areas, replacing the older primitive forms. These older forms were driven outwards from their centres of origin and survived as relict groups in the Southern Hemisphere.
Darlington , modified Matthew's area-climate view of animal distribution. Arguing from the observable facts that larger land areas have more animals and that areas of favourable climate have more animal diversity, he suggested that animals disperse from large to small areas and from favourable climatic to unfavourable climate areas.
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Matthew's idea of dominant, competitive forms evolving under adverse climatic conditions was rejected by Darlington who argued that such conditions would result in cold-adapted tolerant forms. Darlington believed that dominant, more competitive forms evolved in warm climatic regions. Simpson a and b argued that marsupials had entered both South America and Australia by northern routes of entry. He also held that any biotic resemblances between widely separated continental areas could be explained in terms of the probability of long-distance dispersal.
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All the above views depend on the idea of the permanence of continents and oceans through time. Jeannel, ; Noonan, Keast in an analysis of contemporary biotas showed that they were not inconsistent with what we know of the breakup of the large, original land mass Pangea and the two smaller super continents. Laurasia and Gondwanaland. A number of authors e.
Brudin, , ; Cracraft, a and b, ; Fooden, ; Jardine and MacKenzie, ; Raven and Axelrod, ; Schuster, have interpreted present-day plant and animal distributions in terms of continental drift. Some e. Brundin, ; Cracraft, a and b postulate a southern origin page 86 for a number of groups and claim that these migrated northwards from an austral centre of origin. Despite the controversy between the advocates of these two viewpoints in recent years the differences that exist are not as significant as they appear to be from the polemical publications of Brundin and Darlington As correctly noted by Cracraft , both involve the concept that as organisms evolve they disperse over the globe.
Both schools have as their basis the recognition of centres of origin, dispersal mechanisms and pathways of dispersal, and interpret the biogeographic history of taxa within the context of this framework. McKenna attempts a reconciliation and Noonan notes that Gondwanaland satisfies the criterion for Darlington's large land mass with favourable climates. Darwin, Hooker and Wallace discussed the origins of the New Zealand biota in their work. Hooker e. What a perplexing case New Zealand does seem: is not the absence of leguminosae, etc. In Hutton proposed that in the lower Cretaceous period an Antarctic continent extended northwards into Polynesia, connecting page 87 Australia with South America and perhaps South Africa; but in an important paper published in he wrote:.
At the same time, these soundings have made it clear how the connection really took place. None arrived from the south because Fuegia was not then in existence.
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