It is especially difficult to measure the value of natural ecosystems.

It may be related to the prevalence of fire in their natural ecosystem.

Water movement can also be important in simulating a natural ecosystem.

It is more difficult to find the importance of productivity in natural ecosystems.

But the same assurance, many scientists say, cannot be given for natural ecosystems.

David has been to over 30 countries, observing various natural ecosystems and wildlife.

These changes are in turn affecting human and natural ecosystems.

The project highlights the ways that development has altered the natural ecosystems.

They have since been introduced into natural ecosystems on three continents.

The net effect could be negative, some scientists say, especially on natural ecosystems.