The human populations are not limited by the carrying capacity of their ecosystems, and they are the only species on Earth that are able to perform such a thing. The main reason for this is that the humans are able to transport resources of all sorts and for all needs from very distant places. Even if there's a very large population surrounded by desert, the humans are still able to survive by simply bringing in the necessary things from other places throughout he means of transportation. Another reason is that the humans are able to change and manipulate their environment to certain extent, being able to provide for themselves even in ecosystems that naturally are nowhere near close to provide those things for them.
DDT stands for dichloro-diphenyl-trichloroethane. The first kind of synthetic/artificial insecticides came into use in the 1940s. The earlier usage of DDT include: a) Killing of malarial vectors, b) Combatting Typhus and other insect borne human diseases, c) As a pest control in crops d) as a pest control in garden, live stock production and even at homes.
The negative impact of DDT could be felt for the first time when the pests that were earlier killed by use of DDT have now become pesticides resistant. In the 1950s in USA, the regulatory measures were adopted to reduce the usage of DDTs as its effects as a pesticides were no more long significant and also it was creating detrimental physical and psychological impacts on the human and environment.
It was in 1972 that the U.S. Environmental Protection Agency cancelled the order for banning the usage of DDT based on the adverse impact it produced on the environment, human and other life forms. Since then continuous studies are being conducted to analyse the impact of DDTs. In some later years it was established that DDT is the cause of producing tumors in liver.
Some of the common negative impacts produced by DDT as per the U.S. Department of Agriculture :
a) The non destructive nature – DDT can not be destroyed and thus it remains persistent in the atmosphere
b) It attacks the tissues of living organisms especially the animals and humans ( fatty tissue)
c) It can penetrate the atmosphere to deeper extent.
Now as per the current stuation, The use of DDT is controlled and other alternatives of pest control organisms is being deduced. As per the treaty of Stockholm Convention on POPs (Persistent organic pollutants) , usage of DDT for malarial control is justified but it puts a restrictive use of DDT as pesticides in other areas.
<span>If a population of medium sized rodents is placed under a selective pressure that yields both very large and very small individuals it was most likely directional selection. I hope that this is the answer that you were looking for and it has actually come to your desired help.</span>
Explanation:
food chain shows only one possible feeding pathway while food web shows numerous feeding pathway
Answer:
i think the answer is the tempereature and plz correct me if i m wrong
