Native fish will not have any negative effect on other species.

But, pesticides will not only kill the mosquitoes but also affect other species which may harm the ecosystem.

The brown tree snakes eat birds’ eggs and reduce bird population in the ecosystem which leads to an imbalance in the ecosystem.

Zebra mussels may compete with the native species leading to decrease in number and finally extinction of the native species.

One reason why an introduced species might be very successful in a new environment could be large food supply or lack of competition for food.

If the food required for the newly introduced species is abundant, it becomes easier for the species to survive and grow in the new ecosystem.

Also, lack of competition for food, due to no other species feeding on the food type required for the newly introduced species leads to the survival, reproduction and growth of this species in the new ecosystem.

Correct Answer – Option 2 – recycling of nutrients

The mulching lawn movers cuts the grass clippings into very fine pieces and deposit them into soil do ensure decomposition and formation of nutrients to be utilized by the grass for growth. Hence, the recycling of nutrients takes place.

However this process does not ensure increasing the diversity of life, or control of pathogens or the production of new species. Hence, options 1,3 and 4 are incorrect.

Correct Answer – Option 1 – Human actions are a threat to equilibrium in ecosystems.

The diagram above represents modifications of ecosystem by humans through the use of technology, consumption and population growth disrupting the equilibrium in ecosystems.

Hence, the options 2,3 and 4 are incorrect.

• increased sediments
• pollution
• overfishing
• cutting down trees

• increased burning of fossil fuels
• more vehicles used
• increased in levels of deforestation
• increase in population