Community Ecology: Structure, Species Interactions, Succession, and Sustainability

1. Community Ecology: Structure, Species Interactions, Succession, and Sustainability G. Tyler Miller’s Living in the Environment 13th Edition Chapter 8

2. Key Concepts • Community structure • Roles of species • Species interactions • Changes in ecosystems • Stability of ecosystems

3. Flying foxes: keystone species Durian fruit  depend on flying foxes (bats) Mutualism (interaction where both benefit) Flying foxes  endangered…deforestation, hunting (pests) Keystone species: an organism that plays roles affecting many other organisms in an ecosystem. FF pollinate many plants, disperse seeds in their droppings, other species depend on them. Loss of keystone species can lead to loss of pollination of economically important fruits, medicinal plants, trees, fibers, dyes, fuel.

4. Durian fruit, banned in public spaces

5. Flying fox

6. The story of flying foxes and durians illustrates • 1. the unique role (niche) of each species in a community or ecosystem • 2. how interactions between species can affect ecosystem structure and function.

7. Community StructureEcologists use four characteristics to describe a biological community. • Physical Appearance: Stratification, relative sizes and distribution of its population and species • Species diversity (richness): Number of different species in a community • Species abundance: Number of individuals of each species • Niche structure: number of ecological niches, how they resemble or differ from each other and how they interact (species interactions)

8. Community Structure: Appearance and Species Diversity The types, relative sizes, and stratification of plant species in various terrestrial communities or ecosystems (also seen in aquatic systems) vary. Fig. 8-2p. 166

9. Physical Structures Physical structure within an ecosystem or community can also vary. Usually see large vegetative patches (mosaic) of differing size in large ecosystems or communities. Leads to sharp edges as seen in forest and open field or wider more diverse ecotones(transition zones). Result of the differences in physical structure and properties at ecotones can lead to an edge effect. Differences in the physical structure and properties at boundaries in transitions zone are called edge effects. Habitat fragmentation and increasing edge makes many more species vulnerable to stresses(finding food, mating)

10. Biodiversity: factors that affect species diversity Ants Birds Fig. 8-3 and 8-4 p. 167 • Note: high number of different types of species = low species abundance(a few members of each species) ie. rain forest, coral reef • Latitude: diversity decreases with increase in latitude and altitude • Depth: marine diversity increases with depth to 2000m and decreases until the sea bottom where species diversity is high

11. Biodiversity: factors that affect species diversity Pollution: in aquatic systems diversity decreases with increase in pollution. Terrestrial ecosystems: diversity tends to increase with increasing solar radiation, increasing precipitation, decreasing elevation, and pronounced seasonal variations Number of diatom species Unpolluted stream Polluted stream Number of individuals per diatom species

12. Island Diversity Two factors effect isolatedecosystems (such as an island) diversity: size and degree of isolation (distance from mainland) Theory of Island Biogeography by Robert MacArthur, Edward O. Wilson: balance between two factors Theory of Island biogeography: The rate at which new species immigrate and the rate at which species that already exist on the island become extinct. Immigration and extinction rates are affected by 2 factors 1. size 2. distance from mainland Smaller islands = lower species diversity because of lower immigration rate and higher extinction rates(fewer resources, less diverse habitat) Larger islands of equal size closer to mainland will have higher immigration rates= higher species diversity

13. Theory of Island Biogeography Species equilibrium model: immigration and extinction will reach a point the determines the average number of different species(species biodiversity) Assuming extinction rate are equal, a larger island near a main land will a large equilibrium number of species Also see fig. 8-7 pg. 169

14. Types of Species Species in a community play many different roles in its ecology. Types of Species 1. Native species are those whose original home is in this particular ecosystem. 2. Nonnative species originally evolved in a different ecosystem and migrated or were introduced to a new ecosystem. 3. Indicator species alert us to harmful changes taking place in biological communities. Birds are excellent biological indicators because they are everywhere and are quickly affected b. Some amphibians are also considered indicator species.

15. Types of Species Keystone species: help ecological communities run smoothly; they determine the type and number of community species. Loss of a keystone species has far-reaching ramifications for other species in a community (for example, alligators). Foundation species shape communities by creating and enhancing habitat that benefits other species. Elephants, in breaking and uprooting trees, create forest openings. Ex. Grazing species benefit. The rate of nutrient cycling is increased.

16. General Types of Species (cont.) • Keystone:role in ecosystem of species which is actually more influential than numbers or biomass suggests. • These organism play a pivotal role in the structure and function of ecosystem. Have strong interaction with other species that affect their health and survival. • - Critical roles: pollination, dispersion of seeds, habitat modification, predation, improve ability of plants to absorb nutrients and water, and efficient recycling. • Loss of keystone species can lead to population crashes and extinctions of other species i.e. domino effect. • Ex. Bats, bird disperse seed, beaver build dams for ponds

17. Species Interactions: Competition(species in an ecosystem have activities or resource needs in common) • 5 basic types of interactions • Interspecific/intraspecific competition • Predation • Parasitism • Mutualism • commensalism

18. Competition • Intraspecific competition: between members of the same species for the same resources. Intense. Ex. Plants secret toxins to inhibit growth of own and other plant specifies. • Interspecific competition: between members of 2 or more different species for food, space other limited resources. Fundamental niches are realized if resources are abundant. When not fundamental niches overlap/more competition. Results = migrate, change feeding habit, pop. decline, extinction

19. Species Interactions: Competition(species in an ecosystem have activities or resource needs in common) 5 basic types • Intraspecific competition:within a species for resources and territoriality. • Interspecific competition: between different species for limited resources (niche overlap) • Competing species must: • Migrate to another area • Shift its feeding habits or behavior through evolution and natural selection • Suffer a sharp decline in population • Extinction

20. Species Interactions: Competition • Interference competition: one species influences another’s access to some resource regardless of its abundance. Ex. Hummingbird, plants release toxins in soil to prevent other plants from moving in. • Exploitation competition: Two competing species have roughly equal access but differ in how fast or efficiently they exploit it. ex. Humans and all other species.

21. Species Interactions: Competition • Competitive exclusion principle: by Gauss describes how one species eliminates another in an area through competition for limited resources. Niches cannot overlap completely or one will lose.

22. Resource Partitioning • Resource partitioning: a method to reduce competition, dividing up the resource so that species with similar needs use them at different times, in different ways, or in different places. Ex. Hawks feed during day, owls at night.(evolved adaptation) • Realized niche become part of the species fundamental niche Fig. 8-9 p. 175; Refer to Fig. 7-13 p. 152 & Fig. 8-10 p. 175

23. Species Interactions: Predation • Predator: feeds directly on all or part of a living organism • Prey: organism fed on. • Predator-prey relationship: One organism is clearly harmed. However at the population level there are benefits: improve access to food, and improve the genetic stock. • Prey acquisition: herbivores vs. carnivores (pursue or ambush) • Predator Avoidance: speed, highly developed senses,protective coverings

24. Predator Avoidance by Prey Chemical warfare camouflage camouflage Warning coloration Chemical warfare mimicry Warning coloration Deceptive behavior Deceptive looks

25. Symbiotic Relationships Symbiosis is a relationship in which species live together in an intimate association. There are three types: Parasitism (special form of predation) Mutualism Commensalism

26. Symbiotic Species Interactions: Parasitism • Parasite: organisms that feeds on another by living in or on another living organism. Parasite benefits. A form of predation • Host: Organism that a parasite feeds on and lives in or on. Host is harmed. (rarely killed) • Endoparasites: parasites found inside the host organisms body. Ex.tapeworms,disease causing microorganisms. • Ectoparasites: organisms found outside the host organisms body. Ex. Fleas, ticks, mosquitoes

27. Symbiotic Species Interactions: Mutualism • Reproductive mutualism: pollination • Nutritional mutualism : lichens, coral • Nutritional/protection mutualism Fig. 8-12 p. 179

28. Symbiotic Species Interactions: Commensalism • Indirect: i.e., small plants growing in shade of larger plants (redwood sorrel) • Direct: i.e., epiphytes (orchids and bromeliads), remoras Fig. 8-13 p. 180

29. Ecological Succession: Primary With new environmental conditions, community structures can change; one group of species is replaced by another. Primary ecological succession is the gradual establishment of biotic communities on lifeless ground. Primary succession can also take place in newly created small ponds that, over a long period of time, will be transformed to a marsh and finally to dry land.

30. Secondary ecological succession A series of communities with different species developing in places with soil or bottom sediment. The soil or sediment remains after the natural community of organisms has been disturbed, removed, or destroyed. a. Forest fires or deforestation, for example, can convert a particular stage of succession to an earlier stage. b. Changes in vegetation during secondary succession also change the numbers and types of animals and decomposers.

31. Succession and Wildlife Fig. 8-16 p. 182

32. Ecological Stability and Sustainability • Disturbance: can be catastrophic or gradual; human caused or natural. May convert a particular stage of succession to an earlier one. Ex. Fires, drought Refer to Table 8-2 p. 193 • Climax community: end product of succession; stable and predictable community dominated by a few long-loved plant species and in balance with its environment. Known as balance of nature. • This is not actually the case due to several unpredictable small and medium-sized disturbances. Biotic change

33. Disturbances after succession • Intermediate disturbance hypothesis: communities that experience frequent but moderate disturbance have the greatest biodiversity. -create openings for colonizing species

34. Ecological Stability and Sustainability -stability is maintained by constant dynamic change to the environment • Inertia (or persistence): ability of a living system to resist being disturbed or altered. • Constancy: the ability of a living system such as a population to keep its numbers within the limits imposed by available resources. • Resilience: the ability of a living system to bounce back after an external or internal disturbance that is not too drastic.

35. Species Diversity and Ecosystem Stability Many believe that the more diverse the ecosystem the more stable. This is not completely supported. And is difficult to determine Generally we find that ecosystems with more species diversity have a higher net primary productivity, and are more resilient, yet population of individual species can fluctuate. Some level of biodiversity is needed in various ecosystem to provide insurance against catastrophe. Yet, how much biodiversity is needed for this stability is uncertain.

36. Species Diversity and Ecosystem Stability Many ecologists disagree on how to define stability and diversity. Does an ecosystem need both inertia and high resilience to be stable? Ex. Rain forests vs. grasslands. Another difficulty is that populations, communities, and ecosystems are rarely if ever at equilibrium. Instead nature is in a continuing state of disturbance, fluctuation, and change

37. Precautionary Principle Why should we protect our natural systems and biodiversity if it doesn’t lead to increased stability and if nature is mostly unpredictable? Precautionary principle: when evidence indicates that an activity can harm human health or the environment, we should take precautionary measuresto prevent harm even if some of the cause and effect relationships have not been fully established scientifically. The interdependence and connectedness of species, communities and ecosystems are essential features of life on earth