Change in Ecosystems

• Succession is a process of change in community composition and structure, usually towards the establishment of a stable ecosystem. • It includes changes in both the biotic and abiotic factors in an ecosystem over time. • When a stable community is established, it is known as a climax community.

• Primary succession is an ecological succession where a newly formed area is inhabited for the first time by a group of species or a community.

• Change in ecosystem when previous established community is taken over by a new group of organisms • The changes leading up to secondary succession: □ Fire, flood, land clearing □ Interrupts cycling of matter and flow of energy • Secondary succession follows to regain equilibrium but the numbers and kinds of organisms may be different from original ecosystem

○ Catastrophic events (e.g. volcanoes, cyclones, earthquakes, tsunamis) - Leaves barren sites with no soil and no organisms inhabiting the affected area ○ Pioneer species colonise - Autotrophs (e.g. lichens) □ Lichens break down rocks, windblown dust can settle in cracks ○ Soil formation - Shallow soil □ Pioneer species/plants die decompose and form a thin layer of soil □ Mosses can grow □ Mosses die and add nutrients to soil leading to establishment of simple community consisting of bacteria, fungi, invertebrates - Deeper soil □ Grasses, ferns and herbaceous plants can grow □ New plants provide shade □ Roots of new plants speed up weathering of rocks ○ New community formation - Autotrophs attract small herbivores such as insects – becoming the next link in the food chain - More immigrant species join from surrounding areas and remain if they can survive on available resources

○ A natural disturbance occurs ○ Soil formation - Soil is still present with some organic matter - A few organisms may be present ○ New plants - Fast growing pioneer species colonise area and invertebrates enter ecosystem ○ Slower-growing trees begin to grow and stabilise community ○ New herbivores, then carnivores and omnivores arrive and become part of food web ○ A new community forms and eventually becomes a climax community

○ Beginning conditions - A new area with no life (barren) and Begins with disturbance of an already established ecosystem ○ Soil - No soil to start with and Soil is present at beginning ○ Plants - Pioneer species such as lichen first to establish and Seeds and roots of established vegetation already present ○ Biodiversity - Low biodiversity for a long time and Faster development of wider biodiversity ○ Time taken to reach climax community - Hundreds to thousands of years and 50 - 100 years