01/11/2013 LEARNING OBJECTIVES COMMUNITY ECOLOGY INTERSPECIFIC INTERACTIONS MUTUALISM (+/+) TOPIC 26 WE LIVE IN COMMUNITIES

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TOPIC 26 WE LIVE IN COMMUNITIES CEB Textbook Chapter 20, pages 428-437 Mastering Biology, Chapter 20

of interspecific interactions that happen in communities Define in your own words ecological niche, and

Define ecosystem, food web, trophic level and food chain and describe how they relate to one another.

Describe the composition of the levels of an energy pyramid and explain why energy pyramids usually do not

(TOPIC 27 - ECOSYSTEMS) Explain why it takes about the same amount of photosynthetic productivity to produce

environment includes other individuals in its own population and populations of other species living in the

v=u2wohl species living close WeYpY enough together for potential interaction is called a community.

classified according to the effect they have on each population -/- Both populations are harmed. e.g. competition for limited resources +/+ Both populations benefitcial e.

1 TOPIC 26 WE LIVE IN COMMUNITIES CEB Textbook Chapter 20, pages Mastering Biology, Chapter 20 LEARNING OBJECTIVES Describe the four key properties of a community and give examples of the different types of interspecific interactions that happen in communities Define in your own words ecological niche, and competitive exclusion. Define ecosystem, food web, trophic level and food chain and describe how they relate to one another. Define and list examples of producers, primary, secondary, and detritivores in an ecosystem. Describe the composition of the levels of an energy pyramid and explain why energy pyramids usually do not have more than three to five levels. (TOPIC 27 - ECOSYSTEMS) Explain why it takes about the same amount of photosynthetic productivity to produce 10 kilograms of corn or one kilogram of bacon (TOPIC 27 - ECOSYSTEMS) COMMUNITY ECOLOGY An organism s biotic environment includes other individuals in its own population and populations of other species living in the same area. An assemblage of species living close WeYpY enough together for potential interaction is called a community. INTERSPECIFIC INTERACTIONS Interspecific interactions are interactions between different speciesthey can be classified according to the effect they have on each population -/- Both populations are harmed. e.g. competition for limited resources +/+ Both populations benefitcial e.g. mutualism +/- One population is harmed and the other benefits e.g. predation, herbivory (grazing), parasitism MUTUALISM (+/+) In mutualism, both species benefit from an interaction. One example is the rootfungus associations known as mycorrhizae. Another example is plants and their pollinators 1

2 PREDATION (+/-) Numerous adaptations for predator avoidance have evolved in prey populations through natural selection such as Cryptic colouration Warning colouration Mimicry VIDEO: OCTOPUS CAMOUFLAGE wm Mimic Octopus - 2

HERBIVORY (+/-) Herbivory is the consumption of

Plants have evolved numerous defenses against

INTERACTIONS BETWEEN SPECIES IN A COMMUNITY

Species 2 Interaction Exploitation Effect on

LIFE Predation Mutualism Herbivory Parasites

is an organisms role in its community (It s way

3 HERBIVORY (+/-) Herbivory is the consumption of plant parts or algae by an animal. Plants have evolved numerous defenses against herbivory, including spines, thorns, and chemical toxins. FIGURE 20.UN03 Interspecific Interaction Competition INTERACTIONS BETWEEN SPECIES IN A COMMUNITY Effect on Effect on Interspecific Species 1 Species 2 Interaction Exploitation Effect on Effect on Species 1 Species 2 VIDEO: TRIALS OF LIFE Predation Mutualism Herbivory Parasites and Pathogens ECOLOGICAL NICHE Ecological Niche is an organisms role in its community (It s way of life) Each species has a unique niche that it occupies What on earth is a niche? IT IS ABOUT NICHE 3

TYPES OF NICHE Fundamental Niche = The full range of conditions and resources in which the

Realized Niche The niche that is actually used by individuals or the population.

This is a major issue in determining the realised niche of species.

species are too similar they cannot co-exist in the same place COMPETITIVE EXCLUSION

ecological niches Either one species moves away one species changes its niche one species

homogeneous environment (100% niche overlap), one must eventually outcompete the other

4 TYPES OF NICHE Fundamental Niche = The full range of conditions and resources in which the species can maintain a viable population. Assumes the absence of competition. Realized Niche The niche that is actually used by individuals or the population. Assumes that competitors are present to restrict a species to a smaller niche. This is a major issue in determining the realised niche of species. COMPETITION COMPETITIVE EXCLUSION PRINCIPLE States that if the ecological niches of two species are too similar they cannot co-exist in the same place COMPETITIVE EXCLUSION PRINCIPLE The strongest competition is between similar species and is related to ecological niches Either one species moves away one species changes its niche one species becomes extinct GAUSE S EXCLUSION PRINCIPLE If two identical species share a constant, homogeneous environment (100% niche overlap), one must eventually outcompete the other COMPETITION FOR RESOURCES Particularly strong for plants: all share same few limiting resources (light, water, N, P, K...) In a homogeneous environment with a single limiting nutrient, one species will outcompete all others: the one that can survive and reproduce at the lowest resource level strong competitors for light: beech and garlic mustard 4

AVOIDING COMPETITION: VIDEO PLANT PREDATORS Organisms can avoid strong competition by Changing

nocturnal, diurnal Resource partitioning

relationships among the various species in a community.

plants and other photosynthetic organisms to herbivores and then to predators.

ENERGY is the issue! HOW COME? Energy props up each system.

of biomass/energy transfer between trophic levels is called a food chain.

call producers. All organisms in trophic levels above the producers are heterotrophs, or.

5 AVOIDING COMPETITION: VIDEO PLANT PREDATORS Organisms can avoid strong competition by Changing the time they are active e.g. nocturnal, diurnal Resource partitioning e.g. eating different parts of a tree TROPHIC STRUCTURE Trophic structure is the feeding relationships among the various species in a community. A community s trophic structure determines the passage of energy and nutrients(biomass) from plants and other photosynthetic organisms to herbivores and then to predators. IT S ALL ABOUT ENERGY Whether we deal with individuals, populations, communities or ecosystems, ENERGY is the issue! HOW COME? Energy props up each system. NO ENERGY and the whole system crashes down in a heap NO EXCEPTIONS TROPHIC LEVELS The sequence of biomass/energy transfer between trophic levels is called a food chain. The trophic level that supports all other trophic levels consists of autotrophs, which ecologists call producers. All organisms in trophic levels above the producers are heterotrophs, or. TROPHIC LEVELS Primary are called herbivores, which eat plants. Above the level of primary are carnivores, which eat the from the level below. Secondary eat primary. Tertiary eat secondary. Quaternary eat tertiary. FIGURE Quaternary Tertiary Secondary Herbivore Primary Zooplankton Plant Producers Phytoplankton A terrestrial food chain An aquatic food chain 5

TROPHIC LEVELS 3 Secondary The amount of energy here 1 2 Energy is captured By PHOTOSYNTHESIS SUNLIGHT Primary Primary producers determines how many there are in the higher trophic levels More energy

The rate at which an ecosystem s producers convert solar energy to the chemical energy stored in the biomass (organic material) is called primary production FIGURE 20.

6 TROPHIC LEVELS 3 Secondary The amount of energy here 1 2 Energy is captured By PHOTOSYNTHESIS SUNLIGHT Primary Primary producers determines how many there are in the higher trophic levels More energy = more ENERGY IN FOOD CHAINS ONLY FLOWS IN ONE DIRECTION! The rate at which an ecosystem s producers convert solar energy to the chemical energy stored in the biomass (organic material) is called primary production FIGURE Open ocean Estuary Algal beds and coral reefs Desert and semidesert scrub Tundra Temperate grassland Cultivated land Northern coniferous forest (taiga) Savanna Temperate broadleaf forest Tropical rain forest More More More biomass ,000 1,500 2,000 2,500 Average primary production (g/m 2 /yr) More Energy Captured by Photosynthesis LOSS OF ENERGY BETWEEN TROPHIC LEVELS? A large percentage of the energy is lost between trophic levels. This is as a result of the following: Some of the organism cannot be eaten, e.g. bones, fur, etc. Once eaten, some of the organism cannot be digested. Energy is lost in excretory materials, such as urine. Energy is lost in the form of heat from respiration and body heat. TROPHIC LEVELS AND FOOD CHAINS Cat eats bird = Tertiary consumer Caterpillar eats plant = Primary Consumer Plant = Primary Producer Bird eats caterpillar = Secondary Consumer 6

others. Which of these chains is the most efficient?

Energy is lost at all levels in food chains.

trophic levels, so less energy will be lost.

29 Cattle and other livestock are fed grain and cereals.

If a one-acre field of corn is used to feed cows, it can support one

Trophic level Secondary Primary Vegetarians Meat-eaters Cattle

7 WHY AREN T FOOD CHAINS VERY LONG? This tiger is a top predator; the final level in a food chain. HOW ENERGY EFFICIENT IS IT TO EAT MEAT? Food chains can be used to understand why some foods cost more than others. Which of these chains is the most efficient? Most food chains only contain four or five species, why is this? Energy is lost at all levels in food chains. Animals at the top of a long food chain would not get enough energy to survive. The first food chain is the most efficient because it contains fewest trophic levels, so less energy will be lost. IS EATING MEAT LESS ENERGY EFFICIENT? FIGURE Cattle and other livestock are fed grain and cereals. Would it be more energy efficient if humans ate the plant crops instead? If a one-acre field of corn is used to feed cows, it can support one person. Trophic level Secondary Primary Vegetarians Meat-eaters Cattle Producers Corn Corn If the same area is used to feed humans directly, it can support 10 people. Why is so much energy lost? BIOMASS The total amount of living organic material - Biomass is also passed through the food chain and can be converted into energy by respiration FIGURE Plant material eaten by caterpillar 100 kilocalories (kcal) Feces 50 kcal 35 kcal Cellular respiration 15 kcal Growth 7

Energy FOOD WEBS This is a situation where a number of food

Food webs can be very complex and are usually a combination

18 Quaternary, tertiary, and secondary Tertiary and secondary

web Where might there be a connection missing?

DEAD MATERIAL AND DETRITUS Different organisms consume

Scavengers, such as crows and vultures, feast on carcasses.

8 FIGURE 20.UN06 Approximately 90% loss of energy at each trophic level Energy FOOD WEBS This is a situation where a number of food chains, from the same ecosystem, are combined. Food webs can be very complex and are usually a combination of food chains. FIGURE Quaternary, tertiary, and secondary Tertiary and secondary Secondary and primary Primary Producers (plants) A small food web Where might there be a connection missing? Identify the trophic levels Where do the decomposers fit? DEAD MATERIAL AND DETRITUS Different organisms consume detritus. Scavengers, such as crows and vultures, feast on carcasses. Detritivores, such as earthworms and millipedes, primarily consume decaying organic material. Decomposers, mainly prokaryotes and fungi, secrete enzymes that digest molecules in organic material and convert organic materials into inorganic forms. 8

ACTIVITY: FOOD WEBS 01/11/2013 Energy FIGURE 20.

Light Autotrophs Producer Energy Chemical elements

consumer) Detritus Decomposer Inorganic compounds

Complete Mastering Biology Activities listed in Study

Web handout TOPIC 26 COMMUNITIES: LEARNING OBJECTIVES

richness and relative abundance (species evenness).

9 ACTIVITY: FOOD WEBS 01/11/2013 Energy FIGURE 20.UN05 flows one way through the system (yellow arrows) Light Autotrophs Producer Energy Chemical elements Herbivore (primary consumer) Heterotrophs (secondary consumer) Detritus Decomposer Inorganic compounds (chemical elements) FEEDING RELATIONSHIPS HOMEWORK Complete Mastering Biology Activities listed in Study Notes Mastering Biology Assignment Topic 25 Complete Food Web handout TOPIC 26 COMMUNITIES: LEARNING OBJECTIVES CONT: Explain the differences between species diversity, richness and relative abundance (species evenness). Explain the terms Keystone species and Disturbance Explain how predation can help maintain species diversity. 9

INTRODUCING BIODIVERSITY WHAT IS BIODIVERSITY? Biodiversity is a measure of how varied an ecosystem is.

Genetic diversity is a measure of how many variations there are in the genetic code between individuals of a

Species diversity is a measure of how many different species are present in an area (species richness), and how

Habitat diversity is a measure of how many different habitats are present in an area.

Biodiversity hotspots are regions of the world that have a particularly high level of biodiversity but are

10 INTRODUCING BIODIVERSITY WHAT IS BIODIVERSITY? Biodiversity is a measure of how varied an ecosystem is. It can be measured in terms of genes, species or habitats. Genetic diversity is a measure of how many variations there are in the genetic code between individuals of a particular species, or between different species. Species diversity is a measure of how many different species are present in an area (species richness), and how many individuals of these species there are (species evenness). Habitat diversity is a measure of how many different habitats are present in an area. WHAT ARE BIODIVERSITY HOTSPOTS? Biodiversity hotspots are regions of the world that have a particularly high level of biodiversity but are threatened with destruction. There are 34 biodiversity hotspots, all of which contain at least 1,500 endemic species of vascular plants and which have lost 70% of their original habitats. These hotspots account for just 2.3% of the total land area of Earth, but contain at least 50% of all plants, 42% of all terrestrial vertebrates and 29% of all freshwater fish species. FIGURE 20.3 BIODIVERSITY HOTSPOTS Figure Equator 10

Relative abundance of tree species (%) 01/11/2013 WHY MEASURE BIODIVERSITY? What is the point of measuring biodiversity?

and winter. SPECIES RICHNESS When measuring the species diversity of a particular area, an important value is species richness. This is the number of different types of species in a particular area.

So a species with just one individual carries the same weight as a species with a hundred individuals. SPECIES EVENNESS The second component of species diversity is species evenness.

11 Relative abundance of tree species (%) 01/11/2013 WHY MEASURE BIODIVERSITY? What is the point of measuring biodiversity? It enables comparisons to be made: between different areas for example, comparing the biodiversity of one section of woodland with that of a similar type of woodland in another geographical area to see which requires the most protection. in the same area at different times for example, comparing the biodiversity of a group of fields before and after hedgerows have been removed (or replanted), or the biodiversity of a wood in summer and winter. SPECIES RICHNESS When measuring the species diversity of a particular area, an important value is species richness. This is the number of different types of species in a particular area. The greater the number of species, the richer the area. This factor does not take into account the number of individuals of a particular species. So a species with just one individual carries the same weight as a species with a hundred individuals. SPECIES EVENNESS The second component of species diversity is species evenness. This is a comparison of the size of the population (relative abundance) (i.e. the number of individuals) of different species within a particular area. Species diversity within an area increases as both species richness and species evenness increases. FIGURE Species richness, the number of different species in the community Woodland A Woodland B FIGURE Relative abundance of the different species, the proportional representation of a species in a community Tree species Key Woodland A Woodland B COMPARING BIODIVERSITY To compare biodiversity, the area(s) must first be sampled to obtain the number and abundance of species. Compare the data from two fields in the table below. Which field do you think shows the most biodiversity? Species buttercup dandelion daisy Total Number of individuals Field 1 1,000 Field ,000 Field 1 has more species evenness than field 2 so is considered to have the greater biodiversity. 11

KEYSTONE SPECIES A keystone species is a species whose impact on its community is much larger than its total mass or abundance

Experiments in the 1960s were among the first to provide evidence of the keystone species effect and demonstrated that a sea star

ROLE OF PREDATION: KEYSTONE SPECIES Keystone species principle a species that has a greater influence on community structure

usually through predation on an otherwise dominant competitor or predator Example, the Sea Otter eats sea urchins that would

reduce diversity THE IMPORTANCE OF BIODIVERSITY Low biodiversity isn t necessarily cause for concern the Arctic and Antarctic

What s more important is the loss of biodiversity.

unpredictable and possibly irreversible changes. Ecosystem disruption can ultimately have a significant impact on humans.

12 KEYSTONE SPECIES A keystone species is a species whose impact on its community is much larger than its total mass or abundance indicates. Experiments in the 1960s were among the first to provide evidence of the keystone species effect and demonstrated that a sea star functioned as a keystone species in intertidal zones of the Washington coast. ROLE OF PREDATION: KEYSTONE SPECIES Keystone species principle a species that has a greater influence on community structure (usually increasing diversity) than you would predict based on its numbers alone A keystone species maintains species diversity usually through predation on an otherwise dominant competitor or predator Example, the Sea Otter eats sea urchins that would otherwise eat kelp and reduce diversity Example, The sea star eats mussels that would otherwise outcompete other species and reduce diversity THE IMPORTANCE OF BIODIVERSITY Low biodiversity isn t necessarily cause for concern the Arctic and Antarctic contains habitats that naturally have a low biodiversity compared with tropical rainforests. What s more important is the loss of biodiversity. An ecosystem relies on the interdependence of organisms to maintain stability, and loss of species can cause serious, unpredictable and possibly irreversible changes. Ecosystem disruption can ultimately have a significant impact on humans. HEDGEROWS AND BIODIVERSITY Hedgerows are home to several habitats, and support many different types of insects, birds, small mammals, plants and flowers. Destruction of hedgerows to increase the productivity of arable land can lead to decline in these organisms, which can be essential for maintaining the balance of the ecosystem. Without these, food webs can fall apart, diseases can spread rapidly, and crops can become more susceptible to pests. 12

LOW BIODIVERSITY Low biodiversity in itself can be problematic in certain situations, such as in agriculture.

Individual plants therefore have similar growth patterns, leading to higher yields and less wastage.

In agriculture, growing just one species/variety of crop is called monoculture.

USA s cotton industry in the 1920s and 30s.

The migration the boll weevil an insect that feeds on cotton plants from Mexico to the US between the late 1890s and 1920s,

13 LOW BIODIVERSITY Low biodiversity in itself can be problematic in certain situations, such as in agriculture. Selective breeding creates crops with desirable characteristics and which are very similar. Individual plants therefore have similar growth patterns, leading to higher yields and less wastage. However, the lack of genetic diversity can make the crop as a whole highly susceptible to pests and diseases. In agriculture, growing just one species/variety of crop is called monoculture. THE DANGERS OF MONOCULTURE The economic effects of agricultural monoculture can be illustrated by devastation of the southern USA s cotton industry in the 1920s and 30s. In the early twentieth century, many southern states of the USA grew cotton, but were dependent on just one variety. The migration the boll weevil an insect that feeds on cotton plants from Mexico to the US between the late 1890s and 1920s, was disastrous. It caused massive crop losses, which contributed to the Great Depression of the 1930s. CAUSES OF DECLINING BIODIVERSITY SPECIES DIVERSITY: DEFINITIONS Ecologists have identified four main factors responsible for the loss of biodiversity: 1. habitat destruction and fragmentation, 2. invasive species, 3. overexploitation, and 4. pollution. 13

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