I do agree wid this statement "when the vegetation is altered, animal life also changes". Cuz animals require vegetation for their survival. If the vegetation system is disturbed then the animal system will also get disturbed leading to the extinction or disappearance of animals 
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When vegetation is altered animal life also change as vegetation or plants form the 1st tropic level in a food pyramid and is the most important supports life for the herbivores directly and also supports life of consumers indirectly. therefore it is essential for every tropic level as we go if the vegetation is altered in an ecosystem it effects the whole foodchain.
for example:in a food chain of grass,deer and lions-if the grass are removed the deer s will die of starvation and they will not be able to reproduce as a result for some days the lions will survive by feeding upon the remaining deers but after somedays when all the deers will be finished the lions will also die and become extinct as a result of starvation.this shows that vegetation is very crucial for survival of organisms
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