slides 8.1-8.7

Behavior: the nervous system’s response to a stimulus; it is carried out by the muscular or the hormonal system

Behavior is subject to natural selection

Behavioral ecology is the study of the ecological and evolutionary basis for animal behavior

A behavior that increases reproductive success will increase in the gene pool over generations

Behaviors can include chemical signals to communicate many things:

• Establish dominance

• Find food

• Establish territory

• Reproductive success

Some animal behavior is affected by the animal’s circadian rhythm, a daily cycle of rest and activity

Behaviors such as migration and reproduction are linked to changing seasons, or a circannual rhythm

Daylight and darkness are common seasonal cues

Some behaviors are linked to lunar cycles, which affect tidal movements

In behavioral ecology, a signal is a behavior that causes a change in another animal’s behavior

• organisms respond to changes in their environment through behavior and physiological mechanisms

  • a stimulus is an external or internal signal or combination of signals that causes a response from an organism

Communication is the transmission and reception of signals

Animals communicate using various mechanisms: visual, electrical, chemical, tactile, and auditory signals

• uses include indicating dominance, finding food, establishing territory, ensure reproductive success

• organisms exchange info with one another in response to internal and external signals

  • communication between organisms can change behavior

    • this type of communication is referred to as signaling behavior

• signaling behaviors produce changes in behaviors of other organisms

For example, fruit fly courtship follows a three step stimulus-response chain

• Behaviors can result in differential reproductive success

1. A male identifies a female of the same species and orients toward her

   1. Chemical communication: the male smells a female’s chemicals in the air

   2. Visual communication: he sees the female and orients his body toward hers

2. The male alerts the female to his presence

   1. Tactile communication: the male taps the female with a foreleg

   2. Chemical communication: the male chemically confirms the female’s identity

3. The male produces a courtship song to inform the female of his species

   1. Auditory communication: the male extends and vibrates his wing

If all three steps are successful, the female will allow the male to copulate

Behavior is altered by internal changes or external cues

Plants form responses to herbivory

• Herbivory, animals eating plants is a stress that plants face in any ecosystem

Plants counter excessive herbivory

• With physical defenses such as thorns

• With chemical defenses such as distasteful or toxic compounds

Many animals communicate through odor molecules known as pheromones

When a minnow or catfish is injured, an alarm substance in the fish’s skin disperses in the water, inducing a fright response among fish in the area

Imprinting is a behavior that includes learning and innate components and is generally irreversible

• It is distinguished from other learning by a sensitive or critical period

A sensitive period is a limited developmental phase that is the only time when certain behaviors can be learned

Behaviors are regarded as innate or conditioned (learned)

Innate behaviors are inherited and displayed at birth, correctly executed immediately 

• natural selection favors innate and learned behaviors that increase survival and reproductive success

  • innate behaviors are genetically controlled and can occur without prior experience or training

Learned behaviors are complex and adaptable, often needing environmental stimuli or trial-and-error

• learned behaviors are developed as a result of experience

Cooperative behaviors increases an individual’s fitness and the larger group’s as well

• cooperative behaviors involve teamwork between organisms of the same species

  • increases the fitness of the individual

  • increases the survival of the population

• Kin Selection: organisms are more likely to perform an altruistic behavior for organisms that are their close relatives

• some species have evolved warning traits

  • used to discourage predation

  • called aposematism

  • can be markings, behaviors, and/or chemicals

    • ex: coral snakes have red and yellow banding that indicates the presence of venom to potential predators

    • skunks arch back, raise tail, and stomp their feet before spraying

Energy availability informs many aspects of an organism’s ability to maintain homeostasis and thrive, including:

• Organization

• Thermoregulation

• Metabolism

• Reproductive strategies

Organisms that have a net gain in energy grow or store excess energy

Organisms that have a net loss of energy lose mass and eventually die

Animal form and function are correlated at all levels of organization

• Physical laws constrain strength, diffusion, movement, and heat exchange

• As animals increase in size, their skeletons must be proportionately larger to support their mass

• Evolutionary convergence reflects different species’ adaptations to a similar environmental challenge

Homeostatic processes for thermoregulation involve form, function and behavior

Thermoregulation is the process by which animals maintain an internal temperature within a tolerable range

Endothermic animals generate heat by metabolism; birds and mammals are endotherms

Ectothermic animals gain heat from external sources; ectotherms include most invertebrates, fishes, amphibians, and nonavian reptiles

In general, ectotherms tolerate greater variation in internal temperature, while endotherms are active at a greater range of external temperatures

Endothermy is more energetically expensive than ectothermy

Ectotherms regulate their body temperatures through physiological and behavioral adaptations

• Moving into the sun

• Shivering to increase heat production

• Aggregation or crowding with other individuals

Metabolic rate is the amount of energy an animal uses in a unit of time

Metabolic rate can be determined by

• An animal’s heat loss

• The amount of oxygen consumed or carbon dioxide produced

Basal metabolic rate (BMR) is the metabolic rate of an endotherm at rest at a “comfortable” temperature

• Standard metabolic rate (SMR) is the metabolic rate of an ectotherm at rest at a specific temperature

• Both rates assume a nongrowing, fasting, and non-stressed animal

• Ectotherms have much lower metabolic rates than endotherms of a comparable size

Metabolic rates are affected by many factors besides whether an animal is an endotherm or ectotherm

• Two of these factors are size and activity

Organisms evolved different reproductive strategies that have energetic advantages and disadvantages

Reproductive diapause is temporary suspension of development or reproduction during environmentally unfavorable conditions

• Occurs in insects, mites, and some crustaceans and snails during the pupa development state (metamorphosis)

Trophic structure is the feeding relationships between organisms in a community

• Food chains link trophic levels from producers to top carnivores

A food web is a branching food chain with complex trophic interactions

• Species may play a role at more than one trophic level 

• A change in an energy resource can affect the number and size of trophic levels

• Changes at the producer level can change the number and size of other trophic levels

Primary Producers include autotrophic organisms that capture energy from chemical or physical environmental sources

• Photosynthesis captures the energy in sunlight and converts it to organic molecules

• Chemosynthesis captures energy in the form of small inorganic molecules, often in the absence of sunlight, into organic compounds

Consumers capture energy from organic environmental sources of carbon, such as plants or other animals

• Heterotrophs are consumers and must gain organic compounds from the environment for energy

  • Heterotrophs hydrolyze organic compounds such as carbohydrates, lipids and proteins for energy

    

While energy flows through ecosystems, material cycles.

Examples of material cycles include

• Water Cycle

• Carbon Cycle

• Nitrogen Cycle

• Phosphorus Cycle

• Sulfur Cycle

Many cycles rely on decomposers to circulate compounds, like nitrogen and phosphorus

• Decomposers: organisms that break down organic materials, including soil bacteria and fungi

A population is a group of individuals of a single species living in the same general area

Populations are described by their boundaries and size

• Density is the number of individuals per unit area or volume

• Dispersion is the pattern of spacing among individuals within the boundaries of the population

Population growth is calculated using the formula

dN/dt = B - D

Where:

• dN/dt = change in population size relative to change in time

• B = birth rate

• D = death rate

Populations grow in one of two models:

• Exponential Growth Model: growth under idealized conditions, without constraints

dN/dt = r_maxN

• dN/dt = change in population size relative to change in time

• N = population size

• r_max= maximum per capita growth rate of population

  

As populations grow, ecosystem resources become more scarce and growth slows or stops. These resources are limiting factors.

• Density-dependent factors are produced due to increased population density and tend to be biotic

  • Competition (for food, water, living space, mates), stress, toxic wastes, disease

• Density-independent factors occur regardless of population density and are often abiotic

  • Natural disasters (ex: fires or hurricanes), pollution, temperature changes, nutrient availability

Carrying capacity (K) is the number of organisms in a population that the environment can support

Carrying capacity is due to limiting factors: any factor that limits a population’s size, slowing it or stopping it from growing

Limiting factors can be biotic (food, mates, competition) or abiotic (water, living space, sunlight)

Logistic Growth Model: environmental constraints decrease growth rate over time, as carrying capacity is approached

dN/dt = r_maxN(K-N/K)

• dN/dt = change in population size relative to change in time

• N = population size

• r_max = maximum per capita growth rate of population

• K = carrying capacity

  

Communities consist of all the populations in a given ecosystem

Biodiversity is the diversity of life in all its forms, levels and combinations in an ecosystem

Three components of biodiversity:

• Genetic Diversity: heritable variations in community gene pools

• Species Diversity: the variety of organisms that compose a community

• Ecosystem Diversity: variation amongst an ecosystem’s biotic and abiotic factors

Simpson’s Diversity Index calculates an ecosystem’s diversity, accounting for both number of species (species richness) and relative abundance

• Relative abundance is the proportions of different populations that compose the community

• A value of 1 represents infinite diversity and a value of 0 constitutes no diversity

Simpson’s Diversity Index = 1 - Σ(n/N)²

• n = the total number of organisms of a particular species

• N = the total number of organisms of all species

Communities consist of all the populations in a given ecosystem

• Interspecific interactions occur between populations and may help, harm or have no effect on the species involved

Examples include competition, predation, herbivory, and symbiosis (commensalism, mutualism and parasitism)

Competition occurs when individuals compete for scarce resources

Strong competition leads to the competitive exclusion principle, wherein two species competing for the same, limited resource, cannot coexist in the same place

• Competitive species can coexist if they modify how they live in their environments - this is referred to as resource partitioning

This results in each population occupying its own ecological niche

Ecological niche: the total of a species’ use of biotic and abiotic resources

Predation is where one organism, the predator, kills and eats another, the prey

Both predators and prey are adapted to their niches

• Predator adaptations include claws, fangs, and venom

• Prey adaptations include hiding, herds, alarm calls, and camouflage

Trophic cascades are indirect interactions that can control entire ecosystems. They occur when predators limit the density and/or the behavior of prey, enhancing the survival of lower trophic levels

Ecosystem diversity is all the different habitats, biological communities, and ecological processes, as well as variation within individual ecosystems 

Ecosystems with high diversity are more resilient, or likely to recover following an environmental disturbance

• Disturbance: a process that changes resource availability, brings about increased mortality to populations and/or results in populations changing their dispersal

  • Ex: fire, hurricane, pollution, El Niño, or volcanic eruption

Keystone species exert strong control on their communities due to their ecological roles or niches.

• Typically, they are not overly abundant but have a disproportionate effect on their ecosystems

• If keystone species are removed from their ecosystems, the ecosystem may collapse

Producers or autotrophic organisms supply the ecosystem with organic matter and therefore exert control over the entire ecosystem

Abiotic and biotic factors and their availability dictate which populations will thrive and reproduce

Populations in communities are kept in check by limiting factors

In the absence of limiting factors, population growth will become uncontrolled and the ecosystem may change as a result

• Invasive species are introduced into ecosystems outside of their host range, intentionally or unintentionally

  • Often, these species lack limiting factors (predation, disease) in their new environments and their population increases exponentially

  • Examples of invasive species include Japanese Knotweed, Zebra mussels and Gypsy Moth caterpillars

Ecosystems and ecosystem distribution change over time

Human activity accelerates ecosystem change in many ways

• Diseases have been brought into ecosystems by humans such as Potato Blight and White-Nose Syndrome in bats

  • Potato blight is a protist plant infection that likely originated in Mexico and was introduced to European potato crops by humans

  • White-Nose syndrome is an infectious fungus that is native to Europe and Asia and was introduced to North America

    • Over 70% of infections in North American bats are fatal

Habitat destruction by humans significantly alters ecosystems

Habitat destruction can change and ecosystems can be disturbed by meteorological and geological events

• Biogeographical evidence in the fossil record substantiates the effect of tectonic plate theory on evolution

• The Chicxulub Impact in the Yucatan peninsula caused a global cloud of impact debris that dramatically decreased photosynthesis on Earth and lead to the Cretaceous mass extinction, including dinosaur extinction