Responses to the Environment and Ecology

Responses to the Environment

Behavioral Ecology

• Behavioral ecology: The study of how behaviors arise due to ecology and evolution.
  • Behavior: An animal's response to a stimulus (internal or external).
  • Nature vs. nurture: Considers both genetic and environmental factors.
    • Behaviors allow for survival and reproduction.
    • Subject to natural selection.

Understanding Behavior

• Proximate cause: How a behavior occurs or how it is modified.
  1. What was the stimulus to cause the behavior?
  2. How does the "nurture" component affect behavior (i.e., how do experiences during growth and development influence the response)?
• Ultimate cause: Why a behavior occurs (in context of natural selection).
  1. How does the behavior help the animal survive and reproduce?
  2. How does the "nature" component affect behavior (i.e., what is the evolutionary basis of the behavior)?

Types of Behavior

• Behavior can be innate or learned.
• Innate behaviors: Developmentally fixed.
  • Hereditary, born behaviors, do not need to learn them.
  • Experience during growth has no obvious effect.
• Learned behaviors: Depend on environmental influence.
  • Experiences DO affect these behaviors.
  • High variation in a population.

Innate Behaviors

• Fixed action patterns (FAPs): A sequence of unlearned acts directly linked to a stimulus.
  • Actions are unchangeable.
  • Carried out to completion.
  • Triggered by a sign stimulus (external cue).
  • Example: Stickleback fish.

Innate Behaviors - Stickleback Fish Example

• Male stickleback fish have bright red bellies, unlike females with silver bellies.
• Males are highly territorial and attack other males that enter their territory.
• The color red serves as a sign stimulus, triggering aggression in males.
• Any red color, even if not another fish, can elicit aggression.

Innate Behaviors - Migration

• Migration: A regular, long-distance change in location.
  • Triggered by environmental cues.
    • Sun's position.
    • Earth's magnetic field.
    • Celestial cues.

Innate Behaviors - Communication

• Signal: A stimulus generated and transmitted from one animal to another; animal communication.
  • Examples: visual, auditory, tactile, electrical, chemical.
• Pheromones: Chemicals emitted by members of a species that can affect other members of the same species.
  • Stimulus response chains: When a response to a stimulus serves as the next stimulus for a behavior.
    • Seen in animal courtships.
  • Body movement.
    • Example: Waggle dance in bees.

Innate Behaviors - Waggle Dance in Bees

• Honeybees communicate through body movements called the waggle dance.
• Worker bees gather around a returned forager who shakes its abdomen and forms a figure-eight shape.
• This dance communicates the direction where food can be found.

Innate Behaviors - Directed Movements

• Directed movements: Movements towards or away from a stimulus.
• Kinesis: Random movement in response to a stimulus; non-directional.
• Taxis: Directional movement towards (positive) or away from (negative) a stimulus.
  • Phototaxis: Movement in response to light.
  • Chemotaxis: Movement in response to chemical signals.
  • Geotaxis: Movement in response to gravity.

Learned Behaviors

• Learning: The modification of behavior based on specific experiences.

Learned Behaviors - Imprinting

• Imprinting: A long-lasting behavioral response to an individual.
  • Happens during a sensitive period of development (usually very early in life).
  • Imprinting occurs on the first individual they encounter.
  • Example: Ducks following their mother.

Learned Behaviors - Spatial Learning

• Spatial learning: Establishing memories based upon the spatial structure of the animal's surroundings.
  • Some animals form a cognitive map or use landmarks as environmental cues.
  • Example: Birds finding their hidden nests.

Learned Behaviors - Associative and Social Learning

• Associative learning: The ability to associate one environmental feature with another.
  • Example: Associating monarch butterflies with a foul taste.
• Social learning: Learning through observations and imitations of the observed behaviors.
  • Example: Chimps breaking open oil palm nuts.

Natural Selection and Behavior

• Natural selection favors behaviors (innate or learned) that increase survival and reproduction.
  • Foraging: Food obtaining behavior.
    • Searching for, recognizing, and capturing food items.
    • Animals better at foraging will be more successful in finding food.
  • Mating behaviors: Animals can be monogamous or polygamous (polygyny or polyandry).
    • Sexual dimorphism can result from sexual selection.

Natural Selection and Cooperative Behaviors

• Cooperative behaviors tend to increase fitness.
  • Examples: predator warnings, kin selection, pack behavior.
• Altruism: Selfless behavior.
  • Reduces the individual's fitness but increases the fitness of the rest of the population.
  • Example: Naked mole rat colonies have only one reproducing female (queen), who will only mate with a few males (kings). The other nonreproductive members will sacrifice themselves to protect their queen and kings.

Responses in Plants

• Since photosynthesis is critical to a plant's survival, plants can respond to light.
  • Phototropism: A directional response that allows plants to grow towards (and in some cases away from) a source of light.
  • Photoperiodism: Allows plants to develop in response to day length; plants flower only at certain times of the year.

Plant Defenses

• Plants also have mechanisms of defending themselves against herbivory.
  • Physical defenses: Thorns, trichomes (small plant-like hairs).
  • Chemical defenses: Production of toxic or distasteful compounds.
  • Example: Lima bean plants that are being damaged release volatile chemicals that surrounding lima bean plants can sense, causing them to release compounds making themselves less susceptible to herbivory.

Plant Responses to Soil Composition

• Soil composition can affect plants.
• The pH of soil can affect flower coloring in some plants.
• Nutrients are more accessible at certain pH levels.
• Example: Hydrangea blooms turn different colors based upon soil pH (blue - pH 5, pink - pH 7).

Ecosystems and Energy

Ecosystem Definition

• Ecosystem: the sum of all the organisms living in a given area and the abiotic factors they interact with.
• Biotic factors: living, or once living, components of an environment.
• Abiotic factors: nonliving (physical and chemical properties of the environment).

Laws of Thermodynamics

• 1st law: energy can neither be created nor destroyed, only transferred.
  • Law of conservation of mass - chemical elements are continually recycled in the environment.
• 2nd law: exchanges of energy increase the entropy of the universe.

Energy Balance

• A net gain in energy results in energy storage or growth of an organism.
• A net loss of energy results in loss of mass and eventual death of an organism.

Metabolic Rate

• Metabolic rate: the total amount of energy an animal uses in a unit of time.
  • Can be measured in calories, heat loss, or by the amount of oxygen consumed (or CO_2 produced).
    • Oxygen is used in cellular respiration, and CO_2 is produced as a byproduct.
  • An animal's metabolic rate is related to its body mass.
    • Smaller organisms = higher metabolic rate.
    • Larger organisms = lower metabolic rate.

Body Temperature Regulation

• Organisms use different strategies to regulate body temperature.
  • Endotherms: use thermal energy from metabolism to maintain body temperatures.
  • Ectotherms: use external sources (i.e., sun/shade or other organisms) to regulate their body temperature.

Trophic Levels

• Species can be grouped into trophic levels based upon their main source of nutrition and energy. Example energy pyramid
• Decomposers
• Apex Predators (.01%)
• Third Level Consumers (.1%)
• Secondary Consumers (1%)
• Primary Consumers (10%)
• Primary Producers (100%)

Energy Flow

• Unlike mass, energy CANNOT be recycled.
• The sun constantly supplies energy to ecosystems.

Primary Producers

• Primary producers (autotrophs) use light energy to synthesize organic compounds.
  • Plants, algae, photosynthetic plankton.
  • Some organisms are chemosynthetic (vs. photosynthetic), meaning they produce food using the energy created by chemical reactions.
    • I.e., some bacteria and archaea organisms.

Heterotrophs and Decomposers

• Heterotrophs rely on autotrophs because they cannot make their own food.
  • Primary consumers: Herbivores.
  • Secondary consumers: Carnivores that eat herbivores.
  • Tertiary consumers: Carnivores that eat other carnivores.
  • Decomposers: Get energy from detritus (nonliving organic material; leaves, wood, dead organisms).
    • Include fungi and many prokaryotes.
    • Important for recycling chemical elements.

Trophic Structure

• The trophic structures of a community are determined by the feeding relationships between organisms.
  • Food chain: The transfer of food energy up the trophic levels.
  • Food webs: Linked food chains.
• Arrows show the transfer of energy (i.e., the fish is energy for the bird).

Changes in Energy Availability

• Any changes to the availability of energy can disrupt ecosystems.
  • For example:
    • If energy resources change, so can the number and size of trophic levels (Increase energy, increase trophic levels/size; decrease energy, decrease trophic levels/size).
    • A change at the producer level can affect the number and size of the remaining trophic levels.

Primary Production

• Primary production: The amount of light energy that is converted to chemical energy.
  • Primary producers set a "spending limit" for the entire ecosystems energy budget.
  • Gross primary production (GPP): Total primary production in an ecosystem.
  • Net primary production (NPP): The GPP minus the energy used by the primary producers for respiration (R_2).

Ecosystem NPP

• Satellite images show that different ecosystems have varying NPP.
• Areas with higher NPP include rainforests and some ocean regions.

Secondary Production

• Secondary production: The amount of chemical energy in a consumer's food that is converted to new biomass.
  • The transfer of energy between trophic levels is at around 10% efficiency.

Matter Cycling vs Energy

• Unlike energy, matter cycles through ecosystems.
  • Matter is found in limited amounts, unlike solar energy.
  • Biogeochemical cycles: Nutrient cycles that contain both biotic and abiotic factors.
    • Water, carbon, nitrogen, and phosphorus cycle.

Water Cycle

• Biological importance: Water is essential for all life and influences the rate of ecosystem processes.
• Key processes: Evaporation, condensation, precipitation, transpiration, runoff, groundwater flow.

Carbon Cycle

• Biological importance: Carbon is essential for life and required in the formation of organic compounds.
• Key reservoirs: Fossil fuels, soil, oceans (dissolved), plant and animal biomass, atmosphere.
• Key processes: Photosynthesis, respiration, decomposition, combustion.

Nitrogen Cycle

• Biological importance: Nitrogen is important for the formation of amino acids, proteins, and nucleic acids.
• Key reservoirs: Atmosphere, soil, biomass.
• Key processes: Nitrogen fixation, ammonification, nitrification, denitrification, assimilation.

Phosphorus Cycle

• Biological importance: Phosphorus is important for the formation of nucleic acids, phospholipids, and ATP (energy).
• Key reservoirs: soil, rock, sediments.
• Key processes: Weathering, absorption by plants, consumption by animals, decomposition.

Population Ecology

Populations Definition

• Population: a group of individuals of the same species living in an area
• Population ecology: analyzes the factors that affect population size and how and why it changes over time

Density

• Density: the number of individuals per unit area
  • Can be determined by:
    • Counting the number of individuals in the population (rarely done)
    • Sampling techniques (count small areas, average the areas, and then use the averages to estimate total population size)

Dispersion

• Dispersion: the pattern of spacing among individuals within a population
  • Clumped: individuals gather in patches
  • Uniform: evenly spaced individuals in a population
    • Can be due to territoriality
  • Random: unpredictable spacing; not common

Population Dynamics

• The size of a population is not static, affected by:
  • Births/deaths
  • Immigration/emigration
• Demography: the study of the vital statistics of populations and how they change over time
  • Life table: an age-specific summary of the survival pattern of a population
    • Represented by a survivorship curve

Survivorship Curves

• Type I curve: low death rate during early/middle life and high death rate later in life (e.g., humans)
• Type II curve: constant death rate over the lifespan of the organism (e.g., birds)
• Type III curve: high death rate early in life and lower death rate for those that survive early life (e.g., trees)

Change in Population Size Equation

• The per capita rate of increase can be calculated using this formula:
• \frac{dN}{dt} = B - D
  • Where:
    • \frac{dN}{dt} = Change in Population Size
    • B = Birth Rate
    • D = Death Rate

Growth Models

• There are two models for population growth
  • Exponential Growth
  • Logistic Growth

Exponential Growth Model

• Exponential growth model: a population living under ideal conditions (i.e., easy access to food, abundant food, free to reproduce, etc.)
  • Population grows rapidly

Exponential Growth Details

• A population growing exponentially grows at a constant rate
  • J shaped curve
• Calculated using the formula:
  • \frac{dN}{dt} = r_{max}N

Exponential Growth Practice Problem

• A population of bunnies is growing exponentially. The growth rate of the population, r, is 1.5, and the current population size, N, is 3,000 individuals. How many bunnies are being added to the population each year?
• Solution:
  • \frac{dN}{dt} = r_{max}N
  • r_max = 1.5
  • N = 3000
  • \frac{dN}{dt} = 1.5 * 3000
  • \frac{dN}{dt} = 4500
  • Therefore, 4,500 bunnies are added to the population each year.

Logistic Growth Model

• Logistic growth model: the per capita rate of increase approaches zero as the population size nears its carrying capacity
  • The density of individuals exceeds the system's resource availability

Logistic Growth Formula

• Calculated using the following formula:
  • \frac{dN}{dt} = r_{max}N(\frac{K-N}{K})

Logistic Growth Practice Problem

• A hypothetical population has a carrying capacity of 2,000 individuals, and r_max is 1.0. What is the population growth rate for a population with a size of 1,200 individuals? What is happening to this population?
• Solution:
  • r_max = 1.0
  • K = 2000
  • N = 1200
  • \frac{dN}{dt} = 1.0 * 1200* (\frac{2000-1200}{2000})
  • \frac{dN}{dt} = 480
  • The population is growing by 480 people because it is below carrying capacity.

Population Dynamics Factors

• Populations are influenced by natural selection and environmental factors
• Life history: the traits that affect an organism's schedule of reproduction and survival
  • Three variables affect life history
    • When reproduction begins
    • How often the organism can reproduce
    • The number of offspring produced per reproductive episode

Density Dependent and Independent Selection

• K-selection (density-dependent selection):
  • Selection for life history traits that are sensitive to population density
  • Seen in high-density populations that are close to carrying capacity (K)
• R-selection (density-independent selection):
  • Selection for life history traits that maximize reproductive success
  • Seen in low-density populations with little competition

Density Regulation

• Density-dependent regulation:
  • As a population increases, factors can slow or stop growth by decreasing birth rate and increasing death rate
  • Competition, predation, toxic wastes, territoriality, disease, intrinsic factors (i.e., reproduction rates)
• Density-independent regulation:
  • Factors that exert their influence on population size, but the birth/death rate of a population does not change
  • Weather, climate, natural disasters

Community Ecology

Communities Definition

• Community: a group of populations of different species living closely and capable of interacting

Niche Concept

• Habitat: a place or part of an ecosystem occupied by an organism
• Ecological niche: the role and position a species has in its environment
  • Fundamental niche: the niche potentially occupied by the species if there were no limiting factors (predators, competitors, etc.)
  • Realized niche: the portion of the fundamental niche the species actually occupies

Interspecific Interactions Categories

• Interspecific interactions: interactions of individuals from one species with individuals of another species
  • Competition
  • Predation
  • Herbivory
  • Symbiosis (parasitism, mutualism, commensalism)
  • Facilitation

Competition Details

• Competition: -/- relationship where individuals of different species compete for limited resources
  • Competitive exclusion principle: two species competing for the same resource cannot coexist permanently
    • The competitor with even a slightly better advantage will eliminate the inferior competitor
  • Niche partitioning: natural selection drives competing species into different patterns of resource use, or different niches

Predation Details

• Predation: +/- relationship where one species (predator) kills and eats the other species (prey)
  • Adaptations of both predators and prey have been refined by natural selection
    • Cryptic coloration: camouflage
    • Batesian mimicry: harmless species mimics a harmful one
    • Mullerian mimicry: two or more bad-tasting species resemble each other

Herbivory Details

• Herbivory: +/- relationship where one organism eats part of a plant or algal

Symbiosis Details

• Symbiosis: when 2 or more species live in direct contact with one another
  • Parasitism: (+/-) when one organism (parasite) derives nourishment from another (host)
  • Mutualism: (+/+) when both organisms benefit from the relationship
  • Commensalism: (+/0) when one organism benefits, and the other is neither harmed nor benefited

Facilitation Details

• Facilitation: (+/+ or 0/+) when one species has a positive effect on the survival and reproduction of another without intimate association of symbiosis
  • Common in plant species.

Community Diversity

• Species diversity (biodiversity): the variety of different organisms within a community
  • Species richness: the number of different species
  • Relative abundance: the proportion each species represents of all the individuals in the community
• Note: biodiversity boosts ecosystem productivity. The greater the biodiversity in an ecosystem, the more resilient it is

Community Diversity Practice Problem

• Examine the two-tree communities below. Each has 100 individuals distributed among five tree species (A, B, C, D, and E)
  • Community 1: 20A, 20B, 20C, 20D, 20 E
  • Community 2: 5A, 25B, 15C, 20D, 35E
• What can you conclude about their relative species richness and abundance?
• Answer: Both communities have the same species richness (5 species) but have differing relative abundances of species

Simpson's Diversity Index

• Calculate diversity based on species richness and relative abundance
• \text{Diversity Index} = 1 - \Sigma (\frac{n}{N})^2
  • where:
    • n = Total number of organisms of a particular species
    • N = Total number of organisms of all species
• A high diversity index means high biodiversity; a low diversity index means low biodiversity

Invasive Species Issues

• High-diversity communities are more resistant to invasive species
  • Organisms that become established outside of their native range/ecosystem, usually by human activity
  • A ship bringing produce from another country may have insects in the crates holding the produce
    • Cause harm to the environment
    • Grow and reproduce quickly

Invasive Species Impact

• The intentional or unintentional introduction of an invasive species can allow the species to exploit a new niche that is free of predators or competitors

Keystone Species Importance

• Some species play a more pivotal role than others in a community
• Keystone species: not usually abundant, but other species in an ecosystem rely on them because of their important ecological niches
  • Example: coral
    • Coral reefs serve as a keystone species because many other organisms rely upon it as a source of food and protection
  • Example: honey bees
    • Bees are a keystone species because they serve as pollinators

Maintaining Ecosystem Diversity

• Keystone species, producers, and essential abiotic and biotic factors contribute to maintaining the diversity of the ecosystem
  • If keystone species were to be removed from an ecosystem, it would have a rippling effect
  • Often ecosystems collapse

Disturbances Definition

• Disturbances can also influence species diversity and composition
• Disturbance: an event that changes a community by removing organisms from it or altering resource availability
  • Fires, droughts, human activities, etc.

Ecological Succession

• Ecological succession: the gradual process by which the species composition of a community changes and develops over time after a disturbance
  • Primary succession: a series of changes on an entirely new (previously lifeless) habitat that has not been colonized
  • Secondary succession: a series of changes that clears an existing community but leaves the soil intact

Human Disturbances Impact

• Human activity is the strongest disturbance to an ecosystem
  • The main threats to biodiversity are:
    • Habitat loss
    • Invasive species
    • Overharvesting
    • Global change

Habitat Loss Details

• Habitat loss: single greatest threat to biodiversity
  • Agricultural development and urbanization
  • Clear cutting, cattle grazing, farmland

Overharvesting Details

• Overharvesting: organisms are harvested faster than their population can rebound
  • Harvesting of ivory in elephants (now banned)
  • Overfishing

Global Change Details

• Global change: alterations to climate, atmospheric chemistry, and ecological systems that reduce the capacity of Earth to sustain life
  • Air/water pollution
  • Acid rain
  • CO_2 emissions
  • Ocean acidification

Endangered Species Due to Human Activity

• Human disturbances have led to a significant increase in the number of endangered species
  • Many species that are now threatened could potentially provide food, medicine, and fibers
  • Scientists believe we are currently in a mass extinction

Biogeographical Factors

• Biogeographical factors: large-scale factors that contribute to a range of diversity observed.
  • Latitude: Species are more diverse in tropics than at the poles due to climate.
  • Area: Larger areas are more diverse because they offer a greater diversity of habitats.

Pathogens

• Pathogens: Disease-causing organisms and viruses.
  • Pathogens have the most effect on new habitats or ecosystems with less biodiversity.