# Chapter 5 Population Ecology Populations Growth l Population

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Chapter 5 Population Ecology

Populations Growth l Population Growth l Three factors can affect population size: ¡number of births ¡the number of deaths ¡the number of individuals that enter or leave the population. * Simply put, a population will increase or decrease in size depending on how many individuals are added to it or removed from it

Immigration & Emmigration l. Immigration ¡the movement of individuals into an area, is another factor that can cause a population to grow. l. Emigration ¡the movement of individuals out of an area, can cause a population to decrease in size.

l In 1911, 25 reindeer were introduced on Saint Paul Island in the Pribolofs off Alaska. The population grew rapidly and nearly exponentially until about 1938, when there were over 2000 animals on the 41 -squaremile island. The reindeer badly overgrazed their food supply (primarily lichens) and the population “crashed. ” Only eight animals could be found in 1950. A similar sequence of events occurred on Saint Matthew Island from 1944 through 1966. [After Krebs (1972) after V. B. Scheffer (1951). The Rise and Fall of a Reindeer Herd. Science 73: 356– 362. ]

Exponential Growth Populations growing without restriction! ¡If a population has abundant space and food, and is protected from predators and disease, then organisms in that population will multiply and the population size will increase.

Exponential Growth Exponential growth occurs when the individuals in a population reproduce at a constant rate. Under ideal conditions with unlimited resources, a population will grow exponentially.

Exponential population growth is described by the simple differential equation d. N/dt = r. N where, change in number of individuals (d. N) per Change in time (dt) = growth rate (r. N)

Logistic Growth l. Logistic growth occurs when a population's growth slows or stops following a period of exponential growth. l. As resources become less available, the growth of a population slows or stops. The general, S-shaped curve of this growth pattern, called logistic growth

l Carrying Capacity The number or the largest number of individuals that a given environment can support.

Variations of the Logistic Model l If food becomes scarce, the population will experience an overshoot by becoming larger than the spring carrying capacity and will result in a die-off, or population crash.

environmental resistance. : the sum of the environmental factors (such as drought, mineral deficiencies, and competition) that tend to restrict the biotic potential of an organism

Population-same species, same place, same time l Characteristics of Populations Three important characteristics of a population • geographic distribution • Density • growth rate

Geographic distribution, or range, is a term that describes the area inhabited by a population. Clumped- Most common social, protection, resources Uniform- predator-territoriality Allelopathy Random- less common Resources evenly distributed

Population Density Population density is the number of individuals per unit area l. l The population of saguaro cactus in the desert plant community has a low density, whereas other plants in that community have a relatively high density.

Factors that Restrict the Size of a Population Limiting Factors of Environmental Resistance

Density-Dependent Limiting Factors 1. The degree of influence depends on the size of the population. 2. Examples: competition, predation, parasitism, stress caused by crowding, disease 3. Seldom totally eliminate a population 4. Some populations are self-controlling in that they have mechanisms to reduce competition – delayed maturation caused by malnutrition, migration, cannibalism.

Density-Independent Limiting Factors 1. The degree of influence is not related to population size. 2. Examples: pollution, habitat destruction, natural disasters, weather 3. Usually just reduce the population below the cc. but they have the ability to totally eliminate a population

Density Independent Factors Influencing Populations

Density Dependent Factors Influencing Populations

Types of Species l. Generalist ¡large niches ¡tolerate wide range of environmental variations ¡do better during changing environmental conditions l. Specialist ¡narrow niches ¡ more likely to become endangered ¡ do better under consistent environmental 21 conditions

r and k strategists l Depending upon the characteristics of the organism, organisms will follow a biotic potential or carrying capacity type reproductive strategy The r-strategists (Type III) 1. High biotic potential – reproduce very fast 2. Are adapted to live in a variable climate 3. Produce many small, quickly maturing offspring = early reproductive maturity 4. “Opportunistic” organisms The K-strategists (Type I) 1. Adaptations allow them to maintain population values around the carrying capacity 2. They live long lives 3. Reproduce late 4. Produce few, large, offspring 22

Survivorship Curves k-strategist r-strategist l Survivorship curves show the distribution of individuals in a population according to age l Humans and most mammals have a Type I survivorship curve because death primarily occurs in the older years. l Birds have a Type II survivorship curve, as death at any age is equally probable. l Trees have a Type III survivorship curve because very few survive the younger years, but after a certain age, individuals are much more likely to survive. l /

Community Relationships 24

Types of Species l. Native species normally live and thrive Native species in a particular ecosystem l. Nonnative species are introduced - can Nonnative species be called exotic or alien l. Indicator species serve as early Indicator species warnings of danger to ecosystem- birds & amphibians l. Keystone species are considered of Keystone species most importance in maintaining their ecosystem 25

Identify some of the factors that could cause a change in the number of red crabs on Christmas Island. Predict what would happen to the red crab population as the result of a (1) drought, a (2) hurricane, or the introduction of a (3)predator to the ecosystem.

Christmas Island red crab Gecarcoidea natalis l The land crab that is endemic to Christmas Island in the Indian Ocean. An estimated that 43. 7 million adult red crabs lived on Christmas Island alone. The accidental introduction of the yellow crazy ant is believed to have killed about 10– 15 million of these in recent years. l Christmas Island red crabs are well known for their annual mass migration to the sea to lay their eggs in the ocean.

Christmas Island Land Crab Keystone Species l Christmas Island's biodiversity - land crabs are a keystone species in the forest ecology: they dig burrows, turn over the soil, and fertilise it with their droppings. l Seedlings that were previously eaten by crabs started to grow and, as a result, changed the structure of the forest. l Weeds also spread into the rainforest because there are no crabs to control them.

Factors that Influence Population Size l Density-dependent factors- the size of the population will influence an individual’s probability of survival. l Density-independent factors- the size of the population has no effect on the individual’s probability of survival.

Exponential Growth Model l Intrinsic growth rate- under ideal conditions, with unlimited resources, the maximum potential for growth.

Resource Patitioning

Predation l Predation- the use of one species as a resource by another species. l True predators- kill their prey. l Herbivores- consume plants as prey. l Parasites- live on or in the organism they consume. l Parasitoids- lay eggs inside other organisms.

Mutualism l Mutualism- A type of interspecific interaction where both species benefit.

Commensalism l Commensalism- a type of relationship in which one species benefits but the other is neither harmed nor helped.

Community Ecology l Each species has a particular ecological niche or role that it plays in an ecosystem.

Competitive Exclusion Principle l Two species that have exactly the same requirements cannot coexist in exactly the same habitat.

r-Selected Species Cockroach Dandelion Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate (r) Population size fluctuates wildly above and below carrying capacity (K) Generalist niche Low ability to compete Early successional species

K-Selected Species Saguaro Elephant Fewer, larger offspring High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species

The Giant Panda: Specialized and Endangered l Classic k-strategist = specialist l Feeds exclusively on bamboo (1/3 of body weight) l Habitat fragmentation has created “habitat islands” of bamboo in southwestern China due to human encroachment. l 12 protected reserves in China.

Why Are Panda Faced With Extinction? l Illegal poaching (pelt brings in \$40, 000 -60, 000). l Only one cub per female survives each year. l Gestation period = 22 months l Picky about mates. Find each other through scent, become isolated due to habitat fragmentation. l Habitat islands interrupt natural migration to adjacent areas when bamboo population crashes in local areas. l Approximately 700 panda left between zoos and the wild.

What Are Indicator Species? l Indicator species serve as early warnings of damage to a community. l Birds and butterflies are migratory and are excellent indicators of the environment. They do not return to areas along their migratory routes where deforestation has occurred or where broad spectrum pesticides have been applied. l Amphibians are also a universal indicator of environmental degradation as they respire through their skin.

Indicator Species l As indicator species, amphibians may be sending us an important message about the health of the global environment. l They don’t need us, but we and other species need them. Golden toads – once prevalent in Costa Rica’s cloud forest have disappeared.

Indicator Species in New England Why are species in trouble HIPPCO

What Are Keystone Species? l A keystone species holds a community together, when it disappears, so does the biological community. Elimination of a keystone species dramatically alters the structure and function of a community.

American Alligator – a Keystone Species l Largest North American reptile; only humans are their predator. l Hunted nearly to extinction for exotic meat, and leather to make shoes and pocketbooks, and for sport.

Ecological Niche of American Alligator l Dig gator holes that collect freshwater during the dry season which serve as refuges for aquatic life, and supply freshwater and food for many animals.

Ecological Niche of American Alligator l Alligator nesting mounds serve as nesting and feeding sites for herons and egrets

Ecological Niche of American Alligator l Alligator eat large numbers of predatory gar fish and help maintain healthy numbers of game fish such as bass and bream.

Ecological Niche of American Alligator l As alligators move from gator holes to nesting sites, they keep areas of open water free of invading vegetation. This helps to maintain healthy ecosystems with flowing water.

American Alligator Protection l In 1967, the US Government placed the American alligator on the Endangered Species List, which protected it from hunting. l By 1975, the American alligator populations rebounded successfully.

E. O. Wilson l “The loss of a keystone species is like a drill accidentally striking a power line. It causes lights to go out all over”

Interaction between Species Chapter 5 l Competition ¡The outcome is negative for both groups l Symbiosis ¡Benefits both participants l Predation and parasitism ¡The outcome benefits one and is detrimental to the other.

Symbiosis Recall- endosymbiont theory l Describes a relationship between two organisms ¡beneficial to both ¡enhances each organism’s chance of persisting l Each partner called a symbiont l E. g. reindeer and bacteria in the gut ¡The result is food for reindeer, home for bacteria

Amazing Adaptations l Parasitism l Mutualism and Commensalism

Predation and Parasitism l Relationship is beneficial for predator or parasite and negative for prey or host. l Predation- One organism (predator) feeds on other live organisms (prey). l Parasitism- One organism (the parasite) lives on, in, or within another (the host).

North Woods Ecosystem Population Fluctuations

Carrying Capacity -------------------------K-species exponential r-species

The Food Web of the Harp Seal l Food webs are complex because most species feed on several trophic levels. l Harp seal (shown at 5 th level) ¡Feeds on flatfish (4 th level) ¡But also feed on foods from 2 nd – 4 th ¡A species that feeds on several levels placed in a category one above the highest level it feeds on.

Community Level Interactions Sea Otter Manages Kelp Forest l Indirect and more complicated community wide affects species have on one another. l Sea otter of the Pacific Ocean ¡Came close to extinction because of over hunting for fur ¡Feed on shellfish (abalone, sea urchins) ¡Where sea otters abundant kelp beds abundant and few sea urchins ¡Otters affects the abundance of kelp

Community Level Interactions l Sea otters have community level effect ¡Where more kelp is present more habitat for many species l Keystone species ¡A species that has a large effect on its community or ecosystem l Holistic view ¡Ecological community is more than the sum of its parts

Crash landing ROOST Hindfeet

The Evolution of Life on Earth l Mammals ¡More capable brain and faster metabolism ¡Placental uterus one key to mammalian success

Interaction between Species Chapter 5 l Competition ¡The outcome is negative for both groups l Symbiosis ¡Benefits both participants l Predation and parasitism ¡The outcome benefits one and is detrimental to the other.

Symbiosis Recall- endosymbiont theory l Describes a relationship between two organisms ¡beneficial to both ¡enhances each organism’s chance of persisting l Each partner called a symbiont l E. g. reindeer and bacteria in the gut ¡The result is food for reindeer, home for bacteria

Amazing Adaptations l Parasitism l Mutualism l Commensalism l Amazonian Rain Forest Brazil l The First Agriculture 60 mya –Symbiosis

Extincitions l Polar Bear and Global Warming Amazing Diversity of Organisms & Sea Dragons

Competitive Exclusion Principle l Two species that have exactly the same requirements cannot coexist in exactly the same habitat.

Predation and Parasitism l Relationship is beneficial for predator or parasite and negative for prey or host. l Predation- One organism (predator) feeds on other live organisms (prey). l Parasitism- One organism (the parasite) lives on, in, or within another (the host).

North Woods Ecosystem Population Fluctuations

Carrying Capacity -------------------------K-species exponential r-species

The Food Web of the Harp Seal l Food webs are complex because most species feed on several trophic levels. l Harp seal (shown at 5 th level) ¡Feeds on flatfish (4 th level) ¡But also feed on foods from 2 nd – 4 th ¡A species that feeds on several levels placed in a category one above the highest level it feeds on.

Community Level Interactions Sea Otter Manages Kelp Forest l Indirect and more complicated community wide affects species have on one another. l Sea otter of the Pacific Ocean ¡Came close to extinction because of over hunting for fur ¡Feed on shellfish (abalone, sea urchins) ¡Where sea otters abundant kelp beds abundant and few sea urchins ¡Otters affects the abundance of kelp

Community Level Interactions l Sea otters have community level effect ¡Where more kelp is present more habitat for many species l Keystone species ¡A species that has a large effect on its community or ecosystem l Holistic view ¡Ecological community is more than the sum of its parts

Crash landing ROOST Hindfeet

Fossil Record l Most of what we know of the history of life on earth comes from fossils (SJ Gould) l Give us physical evidence of organisms ¡ Show us internal structure l Uneven and incomplete record of species ¡ We have fossils for 1% of species believed to have lived on earth ¡ Some organisms left no fossils, others decomposed, others have yet to be found. l Other info from ancient rocks, ice core, DNA l The whale as an example Other evidence here

Speciation Northern population Early fox population Spreads northward and southward and separates Arctic Fox Different environmental conditions lead to different selective pressures and evolution into two different species. Southern population Gray Fox Adapted to cold through heavier fur, short ears, short legs, short nose. White fur matches snow for camouflage. Adapted to heat through lightweight fur and long ears, legs, and nose, which give off more heat.

Speciation l Two species arise from one ¡ Requires Reproductive isolation l l l Geographic: Physically separated Temporal: Mate at different times Behavioral: Bird calls / mating rituals Anatomical: Picture a mouse and an elephant hooking up Genetic Inviability: Mules l Allopatric ¡ Speciation that occurs when 2 or more populations of a species are geographically isolated from one another ¡ The allele frequencies in these populations change ¡ Members become so different that can no no longer interbreed ¡ See animation l Sympatric ¡ Populations evolve with overlapping ranges ¡ Behavioral barrier or hybridization or polyploidy

TAKE HOME #2 l Macroevolution is the cumulative result of a series of microevolutionary events ¡Typically seen in fossil record ¡Nobody around to see the small, gene pool changes over time.

COEVOLUTION: Interaction Biodiversity l Species so tightly connected, that the evolutionary history of one affects the other and vice versa. ¡Ant Farmers of the Amazon

Coevolution l Interactions between species can cause microevolution ¡ Changes in the gene pool of one species can cause changes in the gene pool of the other l Adaptation follows adaptation in something of a long term “arms race” between interacting populations of different populations ¡ The Red Queen Effect l Can also be symbiotic coevolution ¡ Angiosperms and insects (pollinators) ¡ Corals and zooxanthellae ¡ Rhizobium bacteria and legume root nodules

And NUH is the letter I use to spell Nutches, Who live in small caves, known as Niches, for hutches. These Nutches have troubles, the biggest of which is The fact there are many more Nutches than Niches. Each Nutch in a Nich knows that some other Nutch Would like to move into his Nich very much. So each Nutch in a Nich has to watch that small Nich Or Nutches who haven't got Niches will snitch. -On Beyond Zebra (1955) Dr. Seuss

Niches l A species functional role in an ecosystem l Involves everything that affects its survival and reproduction ¡ Includes range of tolerance of all abiotic factors ¡ Trophic characteristics ¡ How it interacts with biotic and abiotic factors ¡ Role it plays in energy flow and matter cycling l Fundamental Niche ¡ Full potential range of physical chemical and biological conditions and resources it could theoretically use if there was no direct competition from other species l Realized Niche ¡ Part of its niche actually occupied l Generalist vs. Specialist ¡ Lives many different places, eat many foods, tolerate a wide range of conditions vs few, intolerant… ¡ Which strategy is better in a stable environment vs unstable?

POLLENPEEPERS l POLLENPEEPER EVOLUTION

Number of individuals Niche Overlap Niche separation Generalist species with a narrow niche Niche breadth Region of niche overlap Resource use Generalist species with a broad niche

Competition Shrinks Niches

Competition and Community Diversity • Species evolve to minimize competition and niche overlap • Results in a diverse matrix of differing species within a community

What’s This Niche Stuff Got to do with Evolution and Biodiversity? l Hmmmmm…. l Let’s think about three key points…. ¡The more niches you have in an ecosystem… ¡The more of a generalist species you are… ¡The more of a specialist species you are…

Era Period Millions of Cenozoic years ago Quaternary Today Tertiary 65 Bar width represents relative number of living species Species and families experiencing mass extinction Extinction Mesozoic Cretaceous Jurassic 180 Extinction Triassic 250 Paleozoic 345 Cretaceous: up to 80% of ruling reptiles (dinosaurs); many marine species including many foraminiferans and mollusks. Triassic: 35% of animal families, including many reptiles and marine mollusks. Extinction Permian: 90% of animal families, including over 95% of marine species; many trees, amphibians, most bryozoans and brachiopods, all trilobites. Extinction Devonian: 30% of animal families, Extinction Ordovician: 50% of animal families, Permian Carboniferous Current extinction crisis caused by human activities. Devonian Silurian Ordovician Cambrian 500

Extinction l Local, ecological and true extinction l The ultimate fate of all species just as death is for all individual organisms l 99. 9% of all the species that have ever existed are now extinct ¡ To a very close approximation, all species are extinct l Background vs. Mass Extinction ¡ Low rate vs. 25 -90% of total ¡ Five great mass extinctions in which numerous new species (including mammals) evolved to fill new or vacated niches in changed environments ¡ 10 million years or more for adaptive radiations to rebuild biological diversity following a mass extinction l Extinctions open up new opportunities for speciation and adaptive radiation. . BUT you can have too much of a good thing!

Factors Affecting Extinction Rates l Natural Extinctions ¡ Climate change ¡ Cataclysmic event (volcano, earthquake) l Human Activities ¡ ¡ ¡ ¡ ¡ Habitat Loss/Fragmentation Introduction of exotic/invasive species Pollution Commercial harvesting Accidental killing (tuna nets) Harassing Pet Trade Urbanization Damming/Flooding Agricultural conversion

Extinction in the Context of Evolution l If ¡the environment changes rapidly and ¡The species living in these environments do not already possess genes which enable survival in the face of such change and ¡Random mutations do not accumulate quickly enough then, l All members of the unlucky species may die

Biodiversity l Speciation – Extinction=Biodiversity l Humans major force in the premature extinction of species. Extinction rate increased by 100 -1000 times the natural background rate. l As we grow in population over next 50 years, we are expected to take over more of the earth’s surface and productivity. This may cause the premature extinction of up to a QUARTER of the earth’s current species and constitute a SIXTH mass extinction ¡ Genetic engineering won’t solve this problem ¡ Only takes existing genes and moves them around l Know why this is so important and what we are losing as it disappears….

USING EVOLUTION AND GENETICS TO INFORM CONSERVATION l Eco. Regions Approach ¡ Identifying biodiversity “hotspots” and focusing conservation efforts on maintaining those ecosystems ¡ Ex. Tropics, Appalachian Mountains, etc. l “Umbrella Species” Conservation ¡ Conserve one “sexy”, species and you conserve several others because if the interactions they have with one another ¡ Keystone species concept l Species Survival Plan (SSP) ¡ Zoo captive breeding programs ¡ Population genetics in wild populations l Ex. Cheetahs, Primates, Bears, etc.

Federal and International Legislation l Endangered Species Act (1973) ¡ Protection for endangered and threatened plant and animal species & their habitats l Effectiveness? ? ? Exemptions are often granted if • No alternatives to the project • National or regional significance of project • Benefits outweigh those of any alternatives l CITES (late 1970 s)-prohibits trade and commerce of threatened and endangered species ¡ By 1998: signed by 144 countries

Niche is the species’ occupation and its Habitat location of species (its address) 112

Niche A species’ functional role in its ecosystem; includes anything affecting species survival and reproduction 1. Range of tolerance for various physical and chemical conditions 2. Types of resources used 3. Interactions with living and nonliving components of ecosystems 4. Role played in flow of energy and matter cycling 113

Niche Fundamental niche: set of conditions under which a species might exist in the absence of interactions with other species Realized niche: more restricted set of conditions under which the species actually exists due to interactions with other 114

Biodiversity l. Biodiversity ¡increases with speciation ¡decreases with extinction l. Give-and-take between speciation and extinction changes in biodiversity l. Extinction creates evolutionary opportunities for adaptive radiation of surviving species 115

Coevolution l Evolutionary change ¡ One species acts as a selective force on a second species ¡ Inducing adaptations ¡ that act as selective force on the first species Example: 1. Wolf and Moose 2. Acacia ants and Acacia trees 2. Yucca Plants and Yucca moths 3. Lichen

Extinction l. Background extinction - species disappear at a low rate as local conditions change l. Mass extinction - catastrophic, widespread events --> abrupt increase in extinction rate l. Five mass extinctions in past 500 million years l. Adaptive radiation - new species evolve during recovery period following mass 117

How do species move? l. Humans (accidental and intended) l. Animals (sticky seeds and scat) l. Wind and ocean currents (+ or -) l. Land bridges l. Stepping stone islands ¡affected by climactic changes (glaciation) ¡ocean levels ¡short-term weather patterns 118

Nonnative Species l. Nonnative plant species are invading the nation's parks at an alarming rate, displacing native vegetation and threatening the wildlife that depend on them l. At some, such as Sleeping Bear Dunes National Lakeshore in Michigan, as much as 23 percent of the ground is covered with alien species, and the rate of expansion is increasing dramatically. 119

Indicator Species la species whose status provides information on the overall condition of the ecosystem and of other species in that ecosystem l reflect the quality and changes in environmental conditions as well as aspects of community composition 120

Keystone Species l A keystone is the stone at the top of an arch that supports the other stones and keeps the whole arch from falling ¡ a species on which the persistence of a large number of other species in the ecosystem depends. l If a keystone species is removed from a system ¡ the species it supported will also disappear ¡ other dependent species will also disappear l Examples ¡ top carnivores that keep prey in check ¡ large herbivores that shape the habitat in which other species live ¡ important plants that support particular insect species that are prey for birds ¡ bats that disperse the seeds of plants 121

Species Interaction 122

Competition Any interaction between two or more species for a resource that causes a decrease in the population growth or distribution of one of the species 1. Resource competition 123

Competition 124

Resource Competition 125

Competition Any interaction between two or more species for a resource that causes a decrease in the population growth or distribution of one of the species 1. 2. Resource competition Preemptive competition 126

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Competition Any interaction between two or more species for a resource that causes a decrease in the population growth or distribution of one of the species 1. 2. 3. Resource competition Preemptive competition Competitive exclusion 128

Competitive Exclusion 129

Competition Any interaction between two or more species for a resource that causes a decrease in the population growth or distribution of one of the species 1. 2. 3. 4. Resource competition Preemptive competition Competition exploitation Interference competition 130

Competition 131

PREDATION 132

Predator Adaptations l Prey detection and recognition ¡sensory adaptations ¡distinguish prey from non-prey 133

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Predator Adaptations l Prey detection and recognition ¡sensory adaptations ¡distinguish prey from non-prey l Prey capture ¡passive vs. active ¡individuals vs. cooperative 137

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Predator Adaptations l Prey detection and recognition ¡sensory adaptations ¡distinguish prey from non-prey l Prey capture ¡passive vs. active ¡individuals vs. cooperative l Eating prey ¡teeth, claws etc. 143

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Prey Adaptations l. Avoid detection ¡camouflage, mimics, ¡diurnal/nocturnal 148

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Prey Adaptations l. Avoid detection ¡camouflage, mimics, ¡diurnal/nocturnal l. Avoid capture ¡flee ¡resist ¡escape 153

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Prey Adaptations l. Avoid detection ¡camouflage, mimics, ¡diurnal/nocturnal l. Avoid capture ¡flee ¡resist ¡escape l. Disrupt handling (prevent being eaten) ¡struggle? 157

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Herbivory Herbivore needs to find most nutritious ¡circumvent plant defenses 159

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Herbivory Herbivore needs to find most nutritious ¡circumvent plant defenses Herbivory strong selective pressure on plants ¡structural adaptations for defense ¡chemical adaptations for defense 161

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Herbivory 164

Herbivory 165

Herbivory 166

Symbiosis: Mutualists, Commensalist s and Parasites 167

l Symbiosis and symbiotic relationship are two commonly misused terms l Translation of symbiosis from the Greek literally means “living together” l Both positive and negative interactions 168

Mutualism DEFINITION: An interaction between two individuals of different species that benefits both partners in this interaction 169

Yucca and Yucca Moth l Yucca’s only pollinator is the yucca moth. Hence entirely dependent on it for dispersal. l Yucca moth caterpillar’s only food is yucca seeds. l Yucca moth lives in yucca and receives shelter from plant. 170

Lichen (Fungi-Algae) l. Symbiotic relationship of algae and fungae…results in very different growth formas with and without symbiont. l. What are the benefits to the fungus? 171

Commensalists l. Benefit from the host at almost no cost to the host l. Eyelash mite and humans l. Us and starlings or house sparrows l. Sharks and remora 172

Parasites and Parasitoids l Parasites: draw resources from host without killing the host (at least in the short term). l Parasitoids: draw resources from the host and kill them swiftly (though not necessarily consuming them). 173

Parasitic wasps l. Important parasites of larvae. l. In terms of biological control, how would this differ from predation? ovipositor 174

Ecological Processes 175

Ecological Succession Primary and Secondary Succession gradual & fairly predictable change in species composition with time • some species colonize & become more abundant; • other species decline or even disappear. 176

Ecological Succession Gradual changing environment in favor of new / different species / communities 177

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Primary Succession Glacier Retreat 179

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