The somewhat-predictable series of changes to ecosystems over time is called
(community development / ecological succession / population ecology /
symbiosis development). the first species to colonize barren areas are called
(pioneer / primary / secondary / tolerant) species, and may include lichens and
some grasses.

Ecological succession and pioneer species.

Explanation:

The ecological succession may be defined as the change in the species community with respect to the time. Two main types of succession are primary succession and secondary succession.

The species that occupies the first in the succession is pioneer species. The grasses, lichens can acts as the pioneer species in the primary succession. Secondary succession is faster than primary succession.

Thus, the answer is ecological succession and pioneer species.

answer: tributaries flow into rivers.

wetland is a biome that develops when the water gets accumulated in a land exhibiting a huge depression. these form either seasonally or permanently. the water in the wetland comes from rivers, lakes, ocean, flood, rain or other sources. the wetlands includes mangroves, marshes and peatland.

tributaries flow into the rivers develops a wetland because such water will get deposited in the depression and will restrict the original flow of tributary water. hence, water with low drainage current combines with the river water.