5-3 How Do Communities and Ecosystems Respond to Changing Environmental Conditions? Concept 5-3 The structure and species composition of communities and ecosystems change in response to changing environmental conditions through a process called ecological succession.

Communities and Ecosystems Change over Time: Ecological Succession The types and numbers of species in biological communities can ________________ over time in response to changing environmental conditions… Fires, volcanic eruptions Climate change Clearing of forests to plant crops The normally gradual change in species composition in a given area is called ___________________ ______________________ change ecological succession

Communities and Ecosystems Change over Time: Ecological Succession Two main types of ecological succession…depending on the conditions present at the _______________ of the process ___________________ ecological succession ______________________ecological succession beginning primary secondary

Some Ecosystems Start from Scratch: Primary Succession Primary Succession – the gradual establishment of biotic communities in _______________ areas where there is… __________________ in terrestrial ecosystems No _________________________ in aquatic ecosystems Takes hundreds to ________________ of years Need to build up soils/sediments to provide necessary _________________ lifeless No soil bottom sediment thousands nutrients

Lichens and mosses - _____________ species pioneer Balsam fir, paper birch, and white spruce forest community Figure 5.19: Primary ecological succession: Over almost a thousand years, these plant communities developed, starting on bare rock exposed by a retreating glacier on Isle Royal, Michigan (USA) in northern Lake Superior. The details of this process vary from one site to another. Question: What are two ways in which lichens, mosses, and plants might get started growing on bare rock? Jack pine, black spruce, and aspen Heath mat Small herbs and shrubs Lichens and mosses Exposed rocks Time Fig. 5-19, p. 119

Locations where primary succession would occur? Bare rock exposed by a retreating ________________ Newly cooled _______________ An abandoned __________________ or parking lot Newly created shallow ________________ or reservoir glacier lava highway lake

Some Ecosystems Do Not Have to Start from Scratch: Secondary Succession (1) Secondary Succession – occurs when a series of communities or ecosystems with different species develop in places already ___________________ soil or bottom sediment Begins in an area where an ecosystem has been __________________, removed, or destroyed, but some soil or bottom sediment remains containing disturbed

Locations where secondary succession would occur? Abandoned __________________ _______________ or __________ forests Heavily _______________ streams ________________ land Because some soil or sediment is present, new vegetation can begin to germinate, usually within a few ______________ farmland burned cut polluted flooded weeks

Mature oak and hickory forest Figure 5.20: Natural ecological restoration of disturbed land: This diagram shows the undisturbed secondary ecological succession of plant communities on an abandoned farm field in the U.S. state of North Carolina. It took 150–200 years after the farmland was abandoned for the area to become covered with a mature oak and hickory forest. A new disturbance such as deforestation or fire would create conditions favoring pioneer species such as annual weeds. In the absence of new disturbances, secondary succession would recur over time, but not necessarily in the same sequence shown here. See an animation based on this figure at CengageNOW. Questions: Do you think the annual weeds (left) would continue to thrive in the mature forest (right)? Why or why not? Mature oak and hickory forest Young pine forest with developing understory of oak and hickory trees Shrubs and small pine seedlings Perennial weeds and grasses Annual weeds Time Fig. 5-20, p. 120

Secondary Ecological Succession in Yellowstone Following the 1998 Fire Figure 5.21: These young lodgepole pines growing around standing dead trees after a 1998 forest fire in Yellowstone National Park are an example of secondary ecological succession. Fig. 5-21, p. 120

Some Ecosystems Do Not Have to Start from Scratch: Secondary Succession (2) Primary and secondary succession are important natural __________________ Tend to increase biodiversity Increase species _____________ and interactions among species Both types of succession are examples of ________________ ecological ____________________. Primary and secondary succession can be ______________ by Fires Hurricanes Clear-cutting of forests Plowing of grasslands Invasion by nonnative species services richness natural restoration disrupted

Science Focus: How Do Species Replace One Another in Ecological Succession? Three factors affect the how and _______ of succession Facilitation – one set of species makes an area suitable for species with _______________ niche requirements Ex: Lichens help to build soil Inhibition – some early species _______________ the establishment of and growth of other species Ex: black walnut trees release toxic chemicals that reduce competition from other plants Tolerance – late stage plants are largely ____________ by earlier stage plants Young shade-tolerant trees does not compete with taller, older tree rate different hinder unaffected

Succession Doesn’t Follow a Predictable Path Traditional view of succession Succession proceeds in an ____________ sequence along an expected path until a certain stable type of __________________________ occupies an area Balance of nature or permanent _________________ Current view of succession Ever-_____________ mosaic of patches of vegetation Mature late-successional ecosystems State of continual disturbance and change orderly climax community equilibrium changing

Living Systems Are Sustained through Constant Change The ability to respond to change provides us with _________________ – or the capacity to withstand external ______________ and disturbance Inertia, or __________________ - ability of a living system to survive _______________ disturbances ______________ diverse areas have high persistence Resilience - ability of a living system to be _________________ through secondary succession after a more _________________ disturbance Grasslands can recover quickly after a fire stability stress persistence moderate highly restored severe

Does a tropical rainforest have high or low resilience? Does a tropical rainforest recover quickly after it is cut down or burned? Does a tropical rainforest have high or low resilience? No..the soil loses nutrients quickly Low resilience

Three Big Ideas Certain interactions among species affect their use of _________________ and their population sizes. There are always _____________ to population growth in nature. Changes in environmental conditions cause communities and ecosystems to _____________ alter their species composition and population sizes (ecological succession). resources limits gradually

Review Questions What are some of the main differences between primary and secondary succession? Does a grassland have high persistence (inertia) or high resilience? No soil or bottom sediment Soil present Hundreds to thousands of years New growth in a few weeks Pioneer species High resilience – recovers well