Ecology and Ecosystems QBA Exam 1 Practice Test 2026 - Free Practice Questions and Study Guide

Pioneer species are the first organisms to colonize newly exposed or barren habitats, starting primary succession. Mosses and lichens fit this role well because they can tolerate harsh, nutrient-poor conditions and establish without soil. Lichens, a symbiosis of fungus and algae, chemically weather rock and contribute organic material as they grow and eventually die, helping to form the initial thin soil. Mosses help retain moisture and add organic matter, further developing the soil layer. Once this initial soil is present, it becomes possible for more complex plants to establish, leading to grasses, then shrubs, then trees. So moss and lichens are the classic pioneer species, setting the stage for later successional stages.