Population Distribution and Abundance

Lecture 8∙ September 27, 2018

ecological systems form a hierarchy

Overview of ecology

What characteristics allow the Echinacea to survive, grow, and reproduce in the environment of the prairie grasslands of central North America?

individual

ecological systems form a hierarchy

Overview of ecology

Is the population of this species increasing, decreasing, or remaining relatively constant from year to year?

population

A group of individuals of a single species inhabiting a specific area

How does the environment affect the growth, survival, reproduction, distribution, and abundance of species?

ecology of populations

Overview of population ecology

Saving endangered species

Controlling pest populations

Managing fish and game populations

Controlling disease epidemics

Human population growth

Applications of studying the ecology of populations

Overview of population ecology

New unit: Population Ecology

Population Distribution & Abundance

Life Histories

Population Dynamics

Population Growth

New unit: Population Ecology

Literature Comprehension Quiz (Oct. 9)

Guzzo et al. 2017 PNAS

“Behavioral responses to annual temperature variation alter the dominant energy pathway, growth, and condition of a cold-water predator”

Problem Sets (Oct. 4, Oct. 9)

Reflections (Oct. 11)

Exam (Oct. 16)

10 stages of reading a scientific paper

Optimism (“After all, you’ve been reading words for decades.”)

Fear (“Uh … I don’t think all of these are words.”)

Regret

Corner-cutting

Bafflement (“Why was the average sentence 40 words long? Why did the authors use the word “characterize” five times?”)

Distraction (“How would your life change if you owned a bread maker? You’d have to buy yeast. Is yeast expensive? ”)

Realization that 15 minutes have gone by and you haven’t progressed to the next sentence

Determination

Rage

Genuine contemplation of a career in the humanities

http://www.sciencemag.org/careers/2016/01/how-read-scientific-paper

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How to read a scientific paper

This may take a while!

“Nothing makes you feel stupid quite like reading a scientific journal article”

Don’t stress over the abstract, let the introduction be your guide

The introduction should provide the following information:

Identify the big questions of the field and why they are important

Summarize what has been done already, and what questions remain unanswered

Can you distinguish between the big question and the specific question?

What is the hypothesis the authors are trying to test? What are the predictions of this hypothesis that they will test with their experimental design?

Write these down

Describe the general approach the authors plan to use to answer these outstanding questions

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How to read a scientific paper

Hypotheses vs predictions

Hypothesis is generalizable

Predictions follow directly from each hypothesis

If that were true then…

Directly testable from the experimental design

Observation – The last three times I had orange juice for breakfast before an exam, I made an ‘A’ on the exam.

Hypothesis – Drinking orange juice prior to an exam improves performance.

Predictions –

In a class of students, orange juice drinkers will have higher exam scores than non-orange juice drinkers.

People who do poorly on exams will improve their scores if they start drinking orange juice.

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How to read a scientific paper

Hypotheses vs predictions

Hypothesis is generalizable

Predictions follow directly from each hypothesis

If that were true then…

Directly testable from the experimental design

Practice

Observation – My allergies are worse after I dust my house.

Observation – Grass grows faster in July than in August. Observation – Thin candles burn faster than fat candles

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How to read a scientific paper

Some journals place the methods at the end; it may be useful to refer to them as you read the results

You may also need to reference the supplementary materials online

Chart out the results, and map the methods to each result

This will help you determine if the methods were appropriate or where there may have been experimental biases

You may go back and forth quite a bit as you read through these two sections

Pay attention to sample size, effect size, and statistical measures

Some of this can be best evaluated from the figures

“significant” is a precise statistical term that indicates an observed phenomena is statistically unlikely to be due to chance

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How to read a scientific paper

Spend a minute or two thinking about what the results mean to you, in terms of the original hypothesis

Read the discussion with a skeptic’s eye

Do you agree with the authors’ interpretations of the results?

Do the results support the hypothesis/conclusions?

Are there any alternative explanations for the observed results?

Based on the findings, what do you think is the next step? What questions remain unanswered? What do the results of this study suggest would be most interesting for follow-up study?

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How to read a scientific paper

Tips from grad students, post-docs, profs:

http://www.sciencemag.org/careers/2016/03/how-seriously-read-scientific-paper

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New unit: Population Ecology

Population Distribution & Abundance

Life Histories

Population Dynamics

Population Growth

today’s objectives

Interpret population distributions in light of fundamental and realized niches

Describe the factors that influence distributions of individuals in populations on large and small scales

Understand how ecologists measure abundance and density and the factors that cause variation in these

Distribution

Density

Spatial pattern

Abundance

Age distribution

Birth and death rate

Immigration and emigration rate

Rate of growth

Characteristics of populations

Overview of population ecology

Distribution

Density

Spatial pattern

Abundance

Age distribution

Birth and death rate

Immigration and emigration rate

Rate of growth

Characteristics of populations

Overview of population ecology

Individuals within populations have evolved physiological, anatomical, and behavioral characteristics to compensate for environmental variation

Compensating for environmental variation is metabolically costly

This poses limits on the distribution of species

distribution of species

distribution

The distribution of a species is related to its niche

The niche summarizes the environmental factors that influence growth, survival, and reproduction of a species.

A species’ niche consists of all the factors necessary for its existence

distribution

This space is multidimensional

The distribution of a species is related to its niche

The fundamental niche is the total range of physical environmental conditions that are suitable for existence, in the absence of interactions with other species

The realized niche describes the fraction of the fundamental niche that is actually occupied by a species

The difference between the fundamental niche and the realized niche is usually the result of biotic interactions

Changes near the range boundaries are barriers to further range expansion – one or more environmental variables are beyond the species’ limit of tolerance

distribution

The distribution of a species is related to its niche

The fundamental niche is the total range of physical environmental conditions that are suitable for existence, in the absence of interactions with other species

The realized niche describes the fraction of the fundamental niche that is actually occupied by a species

The difference between the fundamental niche and the realized niche is usually the result of biotic interactions

Changes near the range boundaries are barriers to further range expansion – one or more environmental variables are beyond the species’ limit of tolerance

distribution

The distribution of a species is related to its niche

The fundamental niche is the total range of physical environmental conditions that are suitable for existence, in the absence of interactions with other species

The realized niche describes the fraction of the fundamental niche that is actually occupied by a species

The difference between the fundamental niche and the realized niche is usually the result of biotic interactions

Changes near the range boundaries are barriers to further range expansion – one or more environmental variables are beyond the species’ limit of tolerance

distribution

The distribution of a species is related to its niche

The fundamental niche is the total range of physical environmental conditions that are suitable for existence, in the absence of interactions with other species

The realized niche describes the fraction of the fundamental niche that is actually occupied by a species

The difference between the fundamental niche and the realized niche is usually the result of biotic interactions

Changes near the range boundaries are barriers to further range expansion – one or more environmental variables are beyond the species’ limit of tolerance

distribution

A species fundamental niche is related to the physical limits of the environment

distribution

Geographic range

M. giganteus

M. fuliginosus

The effect of climate might be indirect – through the effect of climate on food, water, and habitat

A species fundamental niche is related to the physical limits of the environment

distribution

Example- Tiger beetle – Cicindela longilabris

240 species of Tiger beetle in N.A.

Often colored; defensive odors; prefer

sandy habitats

A species fundamental niche is related to the physical limits of the environment

distribution

Example- Tiger beetle – Cicindela longilabris

240 species of Tiger beetle in N.A.

Often colored; defensive odors; prefer

sandy habitats

Physiological differences across

wide geographic range?

-or-

Limited by environment in similar

way across wide range?

A species fundamental niche is related to the physical limits of the environment

distribution

Example- Tiger beetle – Cicindela longilabris

240 species of Tiger beetle in N.A.

Often colored; defensive odors; prefer

sandy habitats

Similar temperature

requirements across range

A species fundamental niche is related to the physical limits of the environment

distribution

Beetles probably could not disperse across these lower elevation distances

A species fundamental niche is related to the physical limits of the environment

distribution

Example- Tiger beetle – Cicindela longilabris

240 species of Tiger beetle in N.A.

Often colored; defensive odors; prefer

sandy habitats

Physiological differences across

wide geographic range?

-or-

Limited by environment in similar

way across wide range?

How does the range of barnacles in the intertidal zone relate to the fundamental niche and the realized niche?

distribution

Heat tolerance curves

Heat tolerance is NOT limiting the lower limits of the species distributions

How does the range of barnacles in the intertidal zone relate to the fundamental niche and the realized niche?

distribution

Heat tolerance curves

The upper (vertical) boundaries of the range reflect the fundamental niche and the lower (vertical) boundaries of the range reflect the realized niche.

The upper (vertical) boundaries of the range reflect the realized niche and the lower (vertical) boundaries of the range reflect the fundamental niche.

Both the upper and lower boundaries of the range reflect the fundamental niche.

Both the upper and lower boundaries of the range reflect the realized niche.

How does the range of barnacles in the intertidal zone relate to the fundamental niche and the realized niche?

distribution

Heat tolerance curves

The upper (vertical) boundaries of the range reflect the fundamental niche and the lower (vertical) boundaries of the range reflect the realized niche.

The upper (vertical) boundaries of the range reflect the realized niche and the lower (vertical) boundaries of the range reflect the fundamental niche.

Both the upper and lower boundaries of the range reflect the fundamental niche.

Both the upper and lower boundaries of the range reflect the realized niche.

The distribution of a species is related to its niche

The 20th C was the warmest century in the last 1 million years

Temperatures this century are an average 0.2oC above the mean temperature of the last 500 years

The most rapid warming occurred during the final 30 years of the 20th C

What is likely to happen to fundamental niches as global temperatures increase?

Meta-analysis of 1,700 species Shifts in niche space (average 6.1 km shift toward the poles per decade)

Higher latitude or higher elevation

distribution

The distribution of a species is related to its niche

The 20th C was the warmest century in the last 1 million years

Temperatures this century are an average 0.2oC above the mean temperature of the last 500 years

The most rapid warming occurred during the final 30 years of the 20th C

What is likely to happen to fundamental niches as global temperatures increase?

Meta-analysis of 1,700 species Shifts in niche space (average 6.1 km shift toward the poles per decade)

Higher latitude or higher elevation

distribution

The distribution of a species is related to its niche

Meta-analysis of 1,700 species

Shifts in niche space (average 6.1 km shift toward the poles per decade)

Higher latitude or higher elevation

distribution

What controls the distribution of organisms at small scales (within populations)?

Spatial pattern

Dispersion –

Random

Regular (even)

Clumped

What controls the distribution of organisms at small scale?

Spatial pattern

Three basic patterns:

Random: equal chance of being anywhere

Resources often distributed uniformly

Frequent, random pattern of disturbance

Regular: uniformly spaced

Exclusive use of areas (e.g., territoriality)

Individuals avoid one another

Clumped: unequal chance of being anywhere

Mutual attraction between individuals

Patchy resource distribution

Case study: Distribution of stingless bee colonies

Stingless bees

Don’t sting, but bite

Nest in trees in colonies with > 10,000 workers

Use pheromones to communicate

Some species are highly aggressive, others are not

Spatial pattern

Case study: Distribution of stingless bee colonies

Steve Hubbell and Leslie Johnson 1977

Observed that aggressive species usually forage in groups while non-aggressive species feed singly on widely distributed flowers

Hypothesized that behavior would influence the distribution of stingless bee nests

Surveyed the distribution of stingless bee nests in a tropical dry forest in Costa Rica

Spatial pattern

Case study: Distribution of stingless bee colonies

Steve Hubbell and Leslie Johnson 1977

Observed that aggressive species usually forage in groups while non-aggressive species feed singly on widely distributed flowers

Hypothesized that behavior would influence the distribution of stingless bee nests

Surveyed the distribution of stingless bee nests in a tropical dry forest in Costa Rica

What did they predict about the distribution of nests in aggressive species?

Random

Regular

Clumped

Spatial pattern

Case study: Distribution of stingless bee colonies

Steve Hubbell and Leslie Johnson 1977

Observed that aggressive species usually forage in groups while non-aggressive species feed singly on widely distributed flowers

Hypothesized that behavior would influence the distribution of stingless bee nests

Surveyed the distribution of stingless bee nests in a tropical dry forest in Costa Rica

What did they predict about the distribution of nests in aggressive species?

Random

Regular

Clumped

Spatial pattern

Case study: Distribution of stingless bee colonies

Steve Hubbell and Leslie Johnson 1977

Surveyed the distribution of stingless bee nests in a tropical dry forest in Costa Rica

Spatial pattern

Case study: Distribution of stingless bee colonies

Steve Hubbell and Leslie Johnson 1977

Surveyed the distribution of stingless bee nests in a tropical dry forest in Costa Rica

Spatial pattern

The aggressive species has uniformly distributed nests

The non-aggressive species has randomly distributed nests

Spatial pattern

Creosote bush in Mojave Desert

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Figure 9.9

Case study: distribution of creosote bushes

Spatial pattern

Case study: distribution of creosote bushes

Spatial pattern

How could you test this hypothesis?

Seeds germinate at safe sites

Seeds not dispersed from parent areas

Asexual reproduction

How are individuals distributed on a larger scale, across environmental variation?

Spatial pattern

Abundance = the total number of individuals of a species present in a specified area

Density = # individuals

area

Measuring abundance & density

abundance & density

N = Number of animals in the population

m = Number of animals marked on the first visit

K = Number of animals captured on the second visit

r = Number of recaptured animals that were marked

Measuring abundance & density

MARK-RECAPTURE TECNIQUES

Capture and mark a subset of animals and release, then return at a later time to recapture

r/K = m/N

Assumes: random distribution; no mark effect; no mortality; no migration

abundance & density

How are individuals distributed on a larger scale, across environmental variation?

Spatial pattern

Most species show a clumped distribution, whether they range over a large or small geographic area

American crow

Fish crow

Which factors influence species abundance and density?

Niche characteristics

Conditions toward the edge of the range may lead to physiological stress, which could influence dispersal, habitat selection, and reproductive fitness

abundance & density

Which factors influence species abundance and density?

Body size

John Damuth 1981

307 species of herbivorous mammals

abundance & density

Which factors influence species abundance and density?

What does this figure show about the relative population densities of mammals and birds?

Birds and mammals live at similar population densities

Birds live at higher population densities than equally sized mammals

Birds live at lower population densities than equally sized mammals

abundance & density

Body mass (kg)

Which factors influence species abundance and density?

What does this figure show about the relative population densities of mammals and birds?

Birds and mammals live at similar population densities

Birds live at higher population densities than equally sized mammals

Birds live at lower population densities than equally sized mammals

abundance & density

Which factors influence species abundance and density?

abundance & density

Geographic Range

Habitat Tolerance

Local population size

today’s objectives

Interpret population distributions in light of fundamental and realized niches

Describe the factors that influence distributions of individuals in populations on large and small scales

Understand how ecologists measure abundance and density and the factors that cause variation in these

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Tiger beetle confined to cool environments

Figure 9.3

9-2     Source: Schultz, Quinlan, and Hadley 1992

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Tiger beetle confined to cool environments

Figure 9.3

9-2     Source: Schultz, Quinlan, and Hadley 1992