Question

Please explain all the options in brief.

In a temperate grassland system area of North America, vegetation has been destroyed by fire. What will happen to the net primary productivity and the local ecosystem when rains return in the next season?

1. The grasses will grow back, but the herbivores that lived there will not return, as they would have found new land to live on. Therefore, the net primary productivity would decrease.
2. The grasses will not grow back, therefore the herbivores that lived there will not return. Thus, the net primary productivity would decrease.
3. The grasses will grow back and the herbivores that lived there will probably return. The net primary productivity should also be similar to the previous season.
4. The grasses will grow back and the herbivores that lived there will probably return. The net primary productivity would be less than the previous season.

Answer 1

Net primary productivity is the energy available for the heterotrophic organisms in the food web.basically energy spent on respiration of organisms until all of the energy runs out.

a) fire in temperate grasslands will result in loss of vegetation. but rainfall after a fire will cope up with the situations and new plant growth will be seen in those areas leading to new vegetation with changes in plant growth. but this is not possible that an area where vegetation has occurred again have no herbivores to eat them. therefore it is not possible that herbivore never returns to that place which resulted in decreases in net primary productivity.

b) in this grasses will not grow. this is not possible because succession does take place where once life form existed and destroyed due to some conditions here, fire. so though it might take a long time to balance its environmental conditions grasses will grow.

c) the grasses will grow and the herbivore lived there would return .but net primary productivity cannot remain the same as migration has taken place which decreases the net primary productivity. so if succession had taken place it will take the tie to settle down and not all those who have gone from that place would return in exact same numbers. more chances are that of low no. of herbivore returning to newly inhabited place and hence this is not correct to say that NPP remains the same

d) last option says it all correct that grasses will grow following the rainfall and herbivores will return to the place but because migration has taken place no. of organism returned will be altered and it will result in less NPP compared to already inhabited grassland with stable conditions