Species have similar characteristics, but they are rarely, if not never, identical; the difference between them is variation!
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Answer:
There are several environmental factors that causes changes in the ecosystem and the population of that area such as invasive species, extreme weather, land use change, pollution and disease.
Lets take invasive species as environmental factor. Introduction of invasive species can cause a huge change in the ecosystem and affects the native population in that area. it increases the competition for food resources and decreases the survival rate of their preys.
For example: Water hyacinth (Eichhornia crassipes). It is an invasive plant species that has very bad impact of native population as well as other population, like it reduces biological diversity, oxygen loss, decreased phytoplankton productivity, eliminate plants that animals use for nesting, and alter animal communities by blocking access to the water.
Thus invasive population can affect population by reducing biodiversity, water shortages, decreasing availability and quality of key natural resources, disturb the food chain and can cause natural calamities.
Invasive species affect the resources that native species are using and that decreases the carrying capacity of the native population as it disturbs the whole food chain.
It is a form of natural selection called sexual selection.
Need more information to answer the question.
Adenine will always trancribe to Uracil
Thymine will always transcribe to Adenine
Cytosine will always transcribe to Guanine
Guanine will always trancribe to Cytosine
Answer is CUCAAUGAU