Chapter 7 Community Ecology Core Case Study: Why Should We Care about the American Alligator? Hunters wiped out population to the point of near extinction. Alligators have important ecological role. Figure 7-1 Core Case Study: Why Should We Care about the American Alligator? Dig deep depressions (gator holes). Hold water during dry spells, serve as refuges for aquatic life. Build nesting mounds. provide nesting and feeding sites for birds. Keeps areas of open water free of vegetation. Alligators are a keystone species: Help maintain the structure and function of the communities where it is found. COMMUNITY STRUCTURE AND SPECIES DIVERSITY Biological communities differ in their structure and physical appearance. Figure 7-2 Tropical Coniferous Deciduous Thorn rain forest forest forest forest Thorn scrub Tall-grassShort-grass Desert scrub prairie prairie Fig. 7-2, p. 144 Species Diversity and Niche Structure: Different Species Playing Different Roles Biological communities differ in the types and numbers of species they contain and the ecological roles those species play. Species Diversity and Niche Species diversity: combination of: species richness - the number of different species it contains species evenness - abundance of individuals within each of those species Species Diversity and Niche Structure Niche structure: how many potential ecological niches occur, how they resemble or differ, and how the species occupying different niches interact. Geographic location: species diversity is highest in the tropics and declines as we move from the equator toward the poles. Species Diversity on Islands species equilibrium model at some point the rates of immigration and extinction should reach an equilibrium based on: Island size Distance to nearest mainland TYPES OF SPECIES Native Nonnative Indicator Keystone Foundation species Play different ecological roles in communities. TYPES OF SPECIES Native: those that normally live and thrive in a particular community. Nonnative species: those that migrate, deliberately or accidentally introduced into a community. Invasive species Nonnative (Introduced) They displace native species They lower biodiversity The can adapt very quickly to local habitats They contribute to habitat fragmentation They can reproduce very quickly Importation of Species Ex. The Chinese chestnut had a fungus that spread & virtually eliminated the American chestnut. Kudzu Keystone Species: Major Players Keystone species help determine the types and numbers of other species in a community thereby helping to sustain it. Figures 7-4 and 7-5 Foundation Species: Other Major Players Expansion of keystone species category. Foundation species can create and enhance habitats that can benefit other species in a community. Elephants push over, break, or uproot trees, creating forest openings promoting grass growth for other species to utilize. Indicator Species: Biological Smoke Alarms Species that serve as early warnings of damage to a community or an ecosystem. Presence or absence of trout species because they are sensitive to temperature and oxygen levels. Indicator species: Why are Amphibians Vanishing? Frogs serve as indicator species because different parts of their life cycles can be easily disturbed. Figure 7-3 Adult frog (3 years) Sperm Young frog Tadpole develops into frog Sexual Reproduction Eggs Tadpole Fertilized egg Egg hatches development Organ formation Fig. 7-3, p. 147 Case Study: Why are Amphibians Vanishing? Habitat loss and fragmentation. Prolonged drought. Pollution. Increases in ultraviolet radiation. Parasites. Viral and Fungal diseases. Overhunting. Natural immigration or deliberate introduction of nonnative predators and competitors. SPECIES INTERACTIONS: COMPETITION AND PREDATION Species can interact through competition, predation, parasitism, mutualism, and commensalism. Some species evolve adaptations that allow them to reduce or avoid competition for resources with other species (resource partitioning). Resource Partitioning Each species minimizes competition with the others for food by spending at least half its feeding time in a distinct portion of the spruce tree and by consuming somewhat different insect species. Figure 7-7 The Fundamental Niche The fundamental niche of an organism is described by the full range of environmental conditions (biological and physical) under which the organism can exist. The realized niche of the organism is the niche that is actually occupied. It is narrower than the fundamental niche. This contraction of the realized niche is a result of pressure from, and interactions with, other organisms. Niche Specialization Niches become separated to avoid competition for resources. Figure 7-6 Number of individuals Number of individuals Species 1 Species 2 Region of niche overlap Resource use Species 1 Resource use Species 2 Fig. 7-6, p. 150 SPECIES INTERACTIONS: COMPETITION AND PREDATION Species called predators feed on other species called prey. Organisms use their senses their senses to locate objects and prey and to attract pollinators and mates. Some predators are fast enough to catch their prey, some hide and lie in wait, and some inject chemicals to paralyze their prey. PREDATION Some prey escape their predators or have outer protection, some are camouflaged, and some use chemicals to repel predators. Figure 7-8 camouflage (a) Span worm Fig. 7-8a, p. 153 camouflage (b) Wandering leaf insect Fig. 7-8b, p. 153 Chemical warfare (c) Bombardier beetle Fig. 7-8c, p. 153 Chemical warfare & warning coloration (d) Foul-tasting monarch butterfly Fig. 7-8d, p. 153 Chemical warfare & warning coloration (e) Poison dart frog Fig. 7-8e, p. 153 mimicry (f) Viceroy butterfly mimics monarch butterfly Fig. 7-8f, p. 153 Deceptive looks (g) Hind wings of Io moth resemble eyes of a much larger animal. Fig. 7-8g, p. 153 Deceptive behavior (h) When touched, snake caterpillar changes shape to look like head of snake. Fig. 7-8h, p. 153 SPECIES INTERACTIONS: PARASITISM, MUTUALISM, AND COMMENSALIM Parasitism occurs when one species feeds on part of another organism. In mutualism, two species interact in a way that benefits both. Commensalism is an interaction that benefits one species but has little, if any, effect on the other species. Parasites: Sponging Off of Others Although parasites can harm their hosts, they can promote community biodiversity. Some parasites live in host (micororganisms, tapeworms). Some parasites live outside host (fleas, ticks, mistletoe plants, sea lampreys). Some have little contact with host (dump-nesting birds like cowbirds, some duck species) Mutualism: Win-Win Relationship Two species can interact in ways that benefit both of them. Figure 7-9 (a) Oxpeckers and black rhinoceros Fig. 7-9a, p. 154 (b) Clownfish and sea anemone Fig. 7-9b, p. 154 (c) Mycorrhizal fungi on juniper seedlings in normal soil Fig. 7-9c, p. 154 (d) Lack of mycorrhizal fungi on juniper seedlings in sterilized soil Fig. 7-9d, p. 154 Commensalism: Using without Harming Some species interact in a way that helps one species but has little or no effect on the other. Figure 7-10 ECOLOGICAL SUCCESSION: COMMUNITIES IN TRANSITION New environmental conditions allow one group of species in a community to replace other groups. Ecological succession: the gradual change in species composition of a given area Primary succession: the gradual establishment of biotic communities in lifeless areas where there is no soil or sediment. Secondary succession: series of communities develop in places containing soil or sediment. Succession The process where plants & animals of a particular area are replaced by other more complex species over time. Primary Succession: Starting from Scratch Primary succession begins with an essentially lifeless are where there is no soil (bare rock). Soil formation begins with lichens or moss. Primary Succession Primary begins with a lifeless area where there is no soil (ex. bare rock). Soil formation begins with lichens or moss. Primary Succession ‣ Primary succession refers to colonization of a region where there is no pre-existing community. Examples include: Newly emerged coral atolls, volcanic islands Newly formed glacial moraines Islands where the previous community has been extinguished by a volcanic eruption Hawaii: Local plants are able to rapidly recolonize barren areas Primary Succession ‣ A classical sequence of colonization begins with lichens, mosses, and liverworts, progresses to ferns, grasses, shrubs, and culminates in a climax community of mature forest. In reality, this scenario is rare. Unless there is the formation of a new island or volcanic eruption. Mosses and liverworts Bare rock and lichens Grasses and herbaceous plants Shrubs and fast growing trees Mature, slow growing trees Secondary Succession: Starting Over with Some Help Secondary succession begins in an area where the natural community has been disturbed. Figure 7-12 Fig. 7-12, p. 157 Secondary Succession Secondary succession occurs where an existing community has been cleared by a disturbance that does not involve complete soil loss. Cyclone Such disturbance events include cyclone damage, forest fires, hillside slips and clear-cutting. Clear-cutting reduces ecosystem services provided to humans like oxygen, food, and removal of carbon Forest fire Secondary Succession Because there is still soil present, the ecosystem recovery tends to be more rapid than primary succession, although the time scale depends on the species involved and on climatic and edaphic (soil) factors. Mature forest Bare land Grasses and herbaceous plants Pioneer community (annual grasses) Shrubs and small trees Young fast growing trees Pioneer Communities A succession proceeds in stages, until the formation of a climax community, which is stable until further disturbance. Early successional (or pioneer) communities are characterized by: Simple structure, with a small number of species interactions Pioneer community, Hawaii Broad niches Low species diversity Broad niches Climax Communities In contrast to early successional communities, climax communities typically show: Complex structure, with a large number of species interactions Climax community, Hawaii Narrow niches with typically large old growth plants. High species diversity Large number of species interactions Stages – rock lichen small shrubs large shrubs small trees large trees Land Can We Predict the Path of Succession, and is Nature in Balance? The course of succession cannot be precisely predicted. Succession involves species competing for enough light, nutrients and space which will influence it’s trajectory. ECOLOGICAL STABILITY AND SUSTAINABILITY Inertia (persistence): the ability of a living system to resist being disturbed or altered. Constancy: the ability of a living system to keep its numbers within the limits imposed by available resources. Resilience: the ability of a living system to bounce back and repair damage after (a not too drastic) disturbance. ECOLOGICAL STABILITY AND SUSTAINABILITY Having many different species appears to increase the sustainability of many communities. Human activities are disrupting ecosystem services that support and sustain all life and all economies.