Lecture 23 + 24 Flashcards
The current population of the earth is about
7.5 billion (8.1 billion current)
True or false: People are equally distributed around the earth
False
Stage 1 of demographic transition
Pretransition
Stage 2 of demographic transition
Mortality transition
Stage 3 of demographic transition
Fertility transition
Stage 4 of demographic transition
Stability transition
Rank these countries in order of birth rate from low to high
- spain
- bolivia
- democratic republic of the congo
- usa
- mali
- spain
- usa
- bolivia
- democratic republic of the congo
- mali
True or false: Death rates tend to be higher in poor nations relative to wealthy nations
True
Wealth and development
Wealth is highly associated with a nation’s development
One way to measure development
The Human Development Index (HDI) takes into account several factors, including a nation’s healthcare, quality of life, economics, and education
What pattern of growth has been exhibited by the world’s human population over the last 2,000 years?
Greater than exponential (it’s all about r)
- on a logarithmic scale, exponential growth is a straight line
-> constant rate r dN/dt = rN
Human population growth
- on a logarithmic scale human growth (not a straight line)
- growth rate accelerates: greater than exponential increase
How did we get here? What kind of process would lead to a greater than exponential rate of increase?
Increasing r (largely a function of a shift in birth rates and death rates over human history
Pre-agricultural period population growth
- grew as humans expanded into new territories and developed new tools
- grew slowly over about 1 million years
- ~100,000 years
- hunters and gatherers
- tens of thousands of years to double
- population 5-10 million at the end
Agricultural period population growth
- stimulated human population growth
- population grew more rapidly over 7,000 years
- Began ~10,000 years ago
– Domestication of plants and animals
– Doubling time ~1,000 years
– 500+ million at end of period
Industrial period population growth
- led to increased food production and improved sanitation, nutrition, medical care
- population grew rapidly within three centuries
- ~300 years ago. Our current period
- Advances: Technology, Fossil fuels, Sanitation, Medicine
- Death rates decline
- Doubling time ~50 Years
Differences in birth and death rates (in part) lead to
an uneven population distribution
Death rates
Survivorship curves
Life expectancy: how long a person born in a given year can expect to live on average
How old will the average person born in the USA at year ~2000 be at death? (Or in other words what is their life expectancy?)
75-80 (77), a little higher for women
2000: ~ 77
2019 ~ 79
Africa
2000: ~ 50
2019: ~ 60
Life expectancy
- higher in wealthy nations
- going up around the world
Top 10 leading causes of death in 50 wealthiest countries
Noninfectious disease
1. heart attack
2. stroke
3. lung and tracheal cancers
4. alzheimer’s/dementia
5. obstructive lung disease
6. colorectal cancer
7. diabetes
8. hypertension/heart failure
9. breast cancer
Infectious disease
10. pneumonia
Top 10 leading causes of death in 50 poorest countries
Noninfectious disease
1. heart attack
2. stroke
Infectious disease
3. pneumonia
4. HIV/AIDS
5. diarrheal diseases
6. malaria
7. tuberculosis
Other
8. premature birth
9. malnutrition
10. birth trauma
Infant mortality rate
percentage of infants who die before age 1
- reduces with wealth
- poor countries’ rate ~ 14 times higher
Life expectancy and death rates are influenced by various factors
Wealth (development)
- increased nutrition, health care, sanitation
Average #offspring of an American; average of wealthiest and poorest nations
~ 2
wealthiest nations = ~ 1.6
poorest nations = ~ 5.1
fecundity differs between more developed and less developed nations
Age specific reproduction influences r
People in poorer nations
- reproduce more
- reproduce sooner
- lead to higher r
Developed nations general birth and death rate trends in space
Developed: low birth, low death
Developing: high birth, high death
Difference in fecundity in the USA
average ~3 generations ago = ~6
average ~today = ~2
there has been a decrease in birth rates (and death rates)
Stage 1: pretransition
- before economic development
- death rate high
- birth rate high
- population is relatively low/medium
Stage 2: mortality transition
- death rate decreases
- birth rate stays high
- rapid population growth
- population starts to increase
Stage 3: fertility transition
- death rate stays low
- birth rate decreases
- population growth slows
- population is increasing
- 3 generations ago in USA; beginning of fertility transition
- current generation in latter stages of fertility transition
Stage 4: stability transition
- low birth and death rate
- birth and death rates equal
- zero population growth
- population is high
Stage 5 transition trends
- population declines
- birth rate declines
- death rate declines
Forecasting Future Population Trends is important
- Important for planning (why we have a census)
- Used to gauge resource needs and use
- Infrastructure: schools, transportation, etc.
- Health care and social security/retirement
- Projected pollution, etc.
Global Variation in Human Population Growth
- age structure
- determined by survivorship and age-specific birth rate
- age-structure pyramids (a little bit like life tables)
-> graphically display age structure
-> shape indicates rate of population growth
World population diagram of age-structure pyramid
generally pyramid shaped, more straight down from 10-30, goes out a little bit more at 0-4
Past estimates of population growth were flawed
Did not take into account things like demographic transitions
- When we thought of human history r was going up
- Population growth rate is slowing
- Today population growth rate is still >0% so population is still growing
Uncertainty in Predicting Human Population Growth
- population forecasts
- UN data (9.5 to 13.5 billion by 2100)
As the world develops, it looks like the population is levelling off
What is the carrying capacity for humans on earth?
No correct answer
- estimates have varied widely over the years
1. The average estimate has remained roughly constant – about 10 Billion
2. Variation among estimates has increased over time (normally: with more study and knowledge, precision increases)
These predictions are difficult! Forecasting future populations may depend on K
Consider the history of your starving nation for the past 50 years to present day.
Draw how you think the population size has changed over the last 50 years.
x: time
y: # of people
exponential growing, carrying capacity (k) dotted line in upper half
Consider the history of your starving nation for the past 50 years to present day.
In a second the graph extend the first graph 10 more years to demonstrate the influence of food aid
x: time
y: # of people
we have increased the carrying capacity temporarily and by a little bit, population still continues to grow exponentially
Consider the history of your starving nation for the past 50 years to present day.
What about with birth control and family planning?
Population growth rate still increases, although a little less
Development and population
- 1974: shift from family planning to economic development
- reduction of birth rate seen with:
1. economic development
2. educational opportunities for women
3. empowerment of women
What happened to the environmental impact of the hypothetical nation?
It went up as per capita resource use increased
Resource Use and Population Sustainability
IPAT equation (I=PAT)
- determines human impact
I = impact (environmental)
P = population (size, growth, distribution)
A = affluence (individual consumption)
T = technology (energy–using items)
Which 3 are viewed by the United Nations as the most effective (and reasonable) measures that can be taken to reduce population growth rate?
- development
- education
- empowerment of women
True or false: Reduced population growth rates can be considered problematic in some situations.
True. Population growth can be so low as to be negative, this can cause issues for economies.
True or false: Ecologists have a precise measurement of K for humans on earth.
False. There are so many unknowns that a precise measurement of K on earth is not possible.
In general, which of the following differ between the most developed and least developed nations? (You may select 1 or more answers)
- birth rate
- life expectancy
- top causes of death
- average age of first reproduction
- projected population growth
- demographic stage
- birth rate
- life expectancy
- top causes of death
- average age of first reproduction
- projected population growth
- demographic stage
True or false: We can discount immigration and emigration when considering the population growth rate of a nation
False. This can influence a nation’s population growth rate. Some nations are experiencing high levels of immigration or emigration due to push and pull factors. In fact, population growth or decline in some nations can be due more to immigration and emigration than births and deaths
Which is true about the human consumption of fish? (You may choose one or more answers)
- Wild capture continues to supply the majority of fish
- Aquaculture supplies have increased dramatically in the last 30 years
- Wild fisheries have uniformly been underexploited
- Wild fisheries that are overexploited have little impact on local economies
- Wild capture continues to supply the majority of fish
- Aquaculture supplies have increased dramatically in the last 30 years
What fishery management practice promotes harvesting the highest possible number of fish that still allows for the population to replenish itself _______?
Maximum sustainable yield
Most aquaculture occurs in ______________.
Asia
True or false: From the years 1990 to 2010 there has been a dramatic increase in the total amount of wild capture fish harvested per year.
False
Logistic growth
- Population growth slows as resources become limited
- Populations reach a carrying capacity (K), which is the maximum population size an environment can support
- Logistic growth is sigmoidal or S-shaped
- The logistic equation gives the rate of population growth as a function of rmax, N, and K
Population growth rate formula dN/dt =
rmax (intrinsic growth rate at N close to 0) * N (population size) * (1-N/K) (reduction in growth rate due to crowding)
At what population size should we harvest in order to get the maximize harvest over time of a fish population?
Highest growth rate
- maximum sustainable yield
The Maximum Sustainable Yield (MSY) model developed in the 1930s
Became the primary model for managing many resources (forest harvest in addition to fisheries) after WW II in the 1950s
To harvest above the MSY damages the resource, and leads to lower possible harvests and crashes
To harvest below the MSY was viewed as a waste of a resource that could feed more people and lead to more income and more economic development (according to this 1950s logic)
Maximum Sustainable Yield (MSY) corresponds to the
peak rate of population growth
- peak of upside down bell curve (pop. size by pop. growth rate)
-> in early stages, population growth is slow, simply because there are relatively few individuals to reproduce
-> in later stages, population growth is slow because of greater competition for resources as the carrying capacity is approached
We can modify the logistic growth equation to allow for fish harvesting rate (H):
dN/dt = rN(1-N/K) - H
At the equilibrium condition of no net population growth
dN/dt = 0
and therefore:
rN(1-N/K) = H
Different rates of harvesting (catch)
H1, H2, H3 in ascending order (H2 is MSY)
- harvest level is supported by an equal population growth rate
- curve is described by rN(1-N/K)
Na, Nmsy, Nb, K (carrying capacity)
Fishing level H3
The catch exceeds the ability of the population to grow and keep up – cannot do this for long – leads to a crash
Fishing level H1
There are two stable points where the catch equals the population growth (intersection with growth curve, below Nmsy)
Starting in the 1950s, for several decades this goal of not “wasting” the resource was the dominant approach
Fisheries managed for MSY which is sustainable only to the extent underlying population dynamics (r and k) are understood
Peruvian anchovy crash example
Climate variability (el Niño / la Niña cycle) contributed to crash. During el Niño years, coastal upwelling in Peru is much less –much lower net primary productivity. Both r and K for the anchovy population decrease, making overfishing more likely
- the stock took 20 years to rebuild
Collapse of cod fishery off eastern Canada also due to overfishing, and perhaps also related to climate variability
Haddock fishery on Georges Bank (off coast of Massachusetts) also crashed, again due to overfishing. In 1960s, blamed on Soviet Union – led to expansion of US territorial claims from 3 miles to 200 miles
- but note second crash in 1980s
Environmental variability and fisheries, adult haddock example
Each adult haddock or cod can lay over 1 million eggs each year. Vast majority die, but some survive through larval stages and become adult fish.
In Georges Bank area, survival is best (leading to greatest recruitment of new fish) when eggs and larvae are retained in highly productive waters of the Georges Bank gyre.
Weather patterns (wind) and nearshore oceanographic factors (rings of water off the Gulf Stream) can strongly influence this.
-> (this is more subtle than el Niño effect on Peru upwelling and anchovies).
Widespread declines in North Atlantic fisheries since
1950
Status of global fisheries as of 2010
All are either fully exploited, overexploited, or crashed
What went wrong? Why so many fishery crashes? Why might the MSY approach as applied have failed so widely? One reason is climate variability affecting r and k (la Niña)
- Failure to follow the precautionary principle – attempting to maximize harvest
- Imperfect data on population size, and even more so on factors controlling r and k
- Imperfect data on what fishers are actually harvesting (illegal fishing above quota limits)
- Politics –pressure by fishers to push catch limits higher than suggest by MSY
- Lack of recognition of interaction among species – as haddock population declines (inherent part of MSY management), other competing species (pollock) may increase in abundance, reducing r and k for haddock
- Physical damage to the ecosystem from the methods of fishing (i.e., bottom trawling equipment)
The difference a dredge makes
The severe damage done to sea bottom habitats and organisms by dragging fishing gear over the bottom is chronicled in these images.
The first photo is a normal seafloor community on Georges Bank, and the second shows a similar area after dredges have been used to harvest scallops (completely destroyed).
Over the past 25 years, many improvements in fishery management
- Better political structures and oversight (GPS helps!)
- Better use of precautionary principle
- Limiting access (fewer boats, or fewer days allowed for fishing) rather than a set harvest quota (safer for fishers, in addition to being easier to enforce)
- Consideration of competition among fish species
- Use of no-take Marine Protected Areas (MPAs) and other temporary or permanent closures of areas
Beginning in Dec 1994, three large areas off the coast of Massachusetts closed
to all fishing that used bottom trawls
1995 ish: start of no-take protected areas
crash in 2010 ish (haddock)
- 2009 was bad for haddock reproduction (unusual climate, ocean conditions). Populations fell, which contributed to lower fish catch
- but as importantly, fisheries managers reduced allowable catch to protect populations
-> this worked, and haddock population now at all time high, allowing for future higher catches
- population needed for MSY, top dotted line
- level needed for sustained yield, using precautionary principle (bottom dotted line)
Not only haddock population and fishers harvesting haddock have benefited from marine protected areas. By 2001
- Cod harvest increased by 50%
- Yellowtail flounder harvest increased by 800%
- Smaller, non-commercial species (still part of the food web!) such as sculpin also increased substantially
- And sea scallops’ population increased too
Fishing at the borders
Georges Bank and surrounding areas with a long history of abundance have seen fish stock depletion and collapse of the fisheries. To speed stock recovery, parts of the area have been closed to fishing as Marine Protected Areas (MPAs)
- The highest intensity of fishing occurred right at MPA borders, indicating that fishers expected greater abundance there
The fishing strategy that maximized yield always included at least one marine reserve and fishing strategies that did not include reserves were all less than optimal
Fisherman actually catch fewer fish than when there are no areas closed to fishing
- the optimal number of reserves depended upon the length of the habitat
2018 saw very low harvest of sockeye salmon in Alaska and British Columbia
For many salmon runs in coastal rivers, lowest harvest in 50 years
- The “blob” – unusually warm mass of ocean water (~ 2.8º C warmer than normal) that started in the Gulf of Alaska in fall of 2015. Persisted for 2 years, and grew south to California waters. Probably a result of global climate change
- A critical time in the life cycle of this year’s sockeye salmon. Hatched in wetlands and streams, juvenile sockeye salmon stay in fresh water for a few years before entering the Gulf of Alaska. After two years in the ocean, they return inland to spawn and die. That means sockeye that returned to Alaskan streams this year would have been entering the ocean when the blob appeared
- We think of young juveniles as a critical period for them: They have to grow fast and make enough fat to make it through winter
-> But the blob’s temperatures were 4 to 6 degrees Fahrenheit higher than normal. Because salmon are cold-blooded, their metabolism is driven by temperature, and the juveniles needed more food than usual to survive the blob
Chesapeake Bay has long been the most prolific blue crab fishery in the US
The fishery is diminished because of nitrogen pollution and eutrophication
- Water became cloudier over time, due to excess phytoplankton growth caused by nitrogen pollution
- Cloudier water shades seagrasses, which live on the bottom and require light
-> this leads to loss of seagrass bed area
- Seagrasses provide critical habitat for blue crabs, particularly during 2nd larval stage
- Loss of seagrass was a major cause of decrease in blue crab population
- Some good news: After decades of inadequate management, nitrogen pollution is now decreasing, and seagrasses are starting to recover to larger areas.
Maximum sustainable yields are usually seen when population sizes are ___________.
At medium population densities
Fisheries models of MSY are based most heavily on knowing the population’s ________.
- population growth rate
- carrying capacity
True or false: Harvesting at the mathematical maximum sustainable yield (MSY) can be risky for the long term sustainability of a fishery.
True
True or false: The MSY is set by a governing agency based on biology alone. It is not influenced by social or political factors.
False. The MSY often is influenced by public pressure such as the economic interests of the fishing industry.
Like many environmental issues, the solutions for sustainable fish consumption are complex. While aquaculture provides much needed additional food it also __________.
releases excess nutrients and antibiotics into the environment
True or false: Marine protected areas sometimes do a poor job of protecting fisheries.
True
True or false: Climate change and climate variability can modify the true MSY.
True. Both these factors can influence r and K. Furthermore, they can influence other aspects of ecology and ecosystems which in turn influence r and K.
When modelling fisheries:
- Fixed quota models are risky because slight miscalculations can result in fish population extinction
- Fixed quota models result in multiple maximum sustainable yield population levels
- Fixed effort harvesting reduces the risk of population extinction
- Fixed effort models result in an inability to harvest at maximum sustainable yield
- Fixed quota models are risky because slight miscalculations can result in fish population extinction
- Fixed effort harvesting reduces the risk of population extinction
Fixed quota
Remove the same amount (the MSY) from the population each year
- if the population stayed exactly at the peak of its net recruitment curve (big if), this could work
- population could decline until it was extinct
Fixed effort
The amount harvested increases with the size of the population being harvested
- risk of extinction is much reduced
- yield varies with population size
- nobody can be allowed to make a greater effort than they are supposed to
ex. # of trawler-days
