BIOL 3130 Lecture Notes - Lecture 4: Turtle Excluder Device, Population Viability Analysis, Bycatch
2 May 2018
School
Department
Course
Professor
Survival -typically refers to remaining in a stage (age) class
•
Growth -typically refers to going from one stage class to another
•
Reproduction -typically refers to number of offspring per individual
(usually female)
•
Like most demographic analyses, PVAs focus on key birth and death processes,
acknowledging that not all have equal importance for population growth
•
Vital Rates:
Total population size
•
Brood size
•
Proportion of young
•
*key issue: these data are 'relatively' easy to collect
Demography (what can be measured):
Vital rates determine rate of population growth
•
Population size at time 't' is Nt
•
Nt+1 = (lambda)*Nt
•
>1 -population is growing
•
<1 -population is declining
•
=1 -population is stable
•
Lambda -describes the annual population growth rate
•
For some species, estimate lambda = Nt+1 / Nt
•
Estimating Population Growth:
If population growth was the same every year, prediction would be easy but
spatial variation among populations is also present
•
Variation in population growth:
Model simulations only differing by SD
•
Starting size N0=1000
•
Message: larger SD --> wider range of population outcomes after 50 years
•
Population Growth and Prediction:
Management actions can be determined based on information about which life
stages are most important for population growth
•
Trampling of eggs and hatchlings on beaches
!
Drowning of adult turtles in fishing nets
!
Need to determined which of two major threats to logger head turtles is
most important
•
Matrix population model: see slide
•
Reproductive adults were most important stage
!
Efforts aimed at saving eggs and hatchlings would not reverse
population declines even if they were 100% effective
!
PVAs using population data determined the contributions of different life
stages to population growth:
•
Putting turtle excluder devices in fishing nets to prevent drowning would
produce recovery even if it didn’t eliminate all mortality
•
Crouse et al. and Crowder et al. used PVAs to assist with management of
threatened logger head turtles in southeastern US
•
Identifying Key Life Stages:
27 million tons annually (conservative estimate)
•
Long-lived species (albatross, sea turtle)
•
Low absolute rates of bycatch X huge number of fishers = 10,000 black-
footed Albatross per year in north Pacific
•
Fishing Bycatch: 1/3 -1/4 of all catch
•
5:1 ratio of bycatch:shrimp
•
70,000 bycatch individuals discarded per night in Australian prawn fishery
•
Shrimp Trawling (the worst!!!)
•
Sustainable Harvesting:
Feb 2003: National Marine Fisheries Service (NMFS) issues regulations
requiring the US shrimp trawling fleet to install larger turtle excluder device
(TED) openings
•
Allows turtles to escape while sending shrimp to a pocket at end of net
•
TED: escape hatch near end of shrimp net
•
Existing TEDs are too small for large sea turtles
•
The rule mandates the use of TEDs designed to better protect all sea turtle size
classes while having the least economic impact on the shrimp fishery
•
Shrimp trawling is the single largest documented source of sea turtle mortality in
US
•
Sustainable Exploitation: Proposed TED rule would better protect sea turtles
Doing a lot with a little -data limitations1.
A little variation in reproductive success can have huge impacts on population
growth
2.
Not all life stages are equally important for population growth3.
Putting it all together for conservation -managing for population growth with
limited data
4.
Recall: PVAs
Number of juveniles (Jt) = Nt*Pjt
•
Successfully breeding adults (Abt) = 2*[(Jt)/(Bt)]
•
Number of 2nd year birds (It) = (Jt-1)*(St-1)
•
Potential breeding adults (Apt) = (Nt) -(Jt) -(It)
•
Breeding ratio (Rt) = (Abt)/(Apt)
•
Productivity (Ft) = (Jt)/(Apt)
•
Survival Rates (St) = [(Nt+1) -(Jt+1)] /(Nt)
•
Demography: if we know Nt, Bt and Pjt, we can infer:
Imagine population where Nt+1 = (lambda), and lambda=0.86 with prob 1/2(half
females) and lambda=1.16 with prob 1/2 -within a given year
•
Arithmetic mean of the two lambdas = 1.01 -deterministic (nonrandom) growth
•
N(500) = (100)(1.01^500) = 14,477
•
If you start with 100 individuals and population grows for 500 generations…
•
But population growth is subject to stochasticity (random variation)
•
Now imagine same population (100 individuals growing for 500 generations) but
grow rates vary stochastically either 1.16 or 0.86 among years
•
N(500) = (100) [ (1.16^250) * (0.86^250) ] = 54.8
•
So with both growing rates about equally likely from one year to the next then
population size after 500 generations is….
•
Larger s.d. = wider range of population outcomes
•
Therefore, adding variation to population growth (lambda) usually reduces
population growth
•
Variation in Population Growth:
However, the lack of high-quality data derived from long-term studies, and
uncertainty in model parameters and/or structure, often limit the use of
population models to only a few species of conservation concern
•
The ideal conservation planning approach would enable decision-makers to use
PVAs to assess the effects of management strategies and threats on all species at
the landscape level
•
One of the best options to quantitatively measure the benefits of alternative
conservation actions on the persistence of multiple species is to estimate
the risk of extinction faced by each species using PVA
•
An important shortcoming of the use of population viability analyses is
that they require extensive high quality data derived from long-term studies
and the effect of the conservation actions is generally a guess
•
Conserving biodiversity within limited budgets requires allocating resources to
actions that provide the highest return on investment
•
Selecting reserves in a network that maximizes the viability of one or more
species, communities, or ecosystems
•
Protected area design: optimization
•
Source/sink --> limit number of sinks (D>B)
•
White holes
•
Meta-populations
•
Allee effects
•
Habitat
•
Dangerous edges
•
Extinction debt
•
Sampling effect
•
SLOSS
•
How are each of these relevant for reserve design optimization?
•
Small reserve scenario -metapopulation dynamics were stimulated for
current conditions in which populations are constrained and managed
within individual, fenced, protected areas
i)
Big reserve scenarioii)
Small and Big connectediii)
Big and connectediv)
Bigger and connected, but cheapv)
Biggest reserve scenario vi)
Six scenarios: population viability analysis was performed under six reserve
scenarios, which were developed according to current constraints and future
management opportunities in the study area
•
"Creating Larger and Better Connected Protected Areas Enhances the Persistence of
Big Game Species in the Maputaland-Pondoland-Albany Biodiversity Hotspot"
--> small overlap between protected areas and hot-spots
Population Size
○
Brood Size
○
Proportion of juveniles
○
You’ve been hired to write a recovery plan for the recently listed Woodland
Caribou in northern Ontario -what minimum population data would you need for
a PVA?
1.
N after 10 years in east =(.76^5)(1.34^5)*1000=1095
○
N after 10 years in west = (0.97^5)(1.03^5)*500 = 497
○
You find demographic differences between eastern and western populations.
Eastern populations are twice as large (N=1000). In the west lambda over 10
generations ranges between 0.97 -1.03, whereas eastern populations have a
similar average range between 0.76-1.34. Describe the expected general
differences in population performance between the two populations. Why does
this happen?
2.
This can result in inbreeding, as the number of females decrease
!
Population of females is declining --> total population will not persist
(without a way to reproduce)
○
In east: N after 10 years = (0.57^7.5)(2.12^2.5)*1000=98 (VS 1095)
○
In eastern populations, you find that 75% of the females have a lambda of 0.57
while the rest are highly successful over 10 year period (lambda=2.12). How
does this change the growth projections?
3.
Practice Question:
Occurs when the harvest rate of any given population exceeds its natural
replacement rate, either through reproduction alone in closed populations or
through both reproduction and immigration from other populations
•
Third most important driver of freshwater fish extinction (habitat loss and
degradation have high impacts)
•
Forms: commercial harvests, hunting, fishing
•
Direct and indirect affect on biodiversity (e.g. food webs)
•
Populations are already weakened by climate change
!
Transition into Holocene
○
Ex. Ginseng
!
Ex. Carolinian parakeet -harvested for 1800 fashion (now extinct)
!
Over-exploitation of trees, medicinal plants and animals for their fur still
have echoing impacts today
○
Formed huge stands in forests along 3000km of Brazilian coast line
!
Source of red dye and hardwood
!
1500-1875: over-exploitation (economically extinct)
!
Only found in arboretums and a few protected areas
!
Message: highly abundant species can be as vulnerable as rare
species
!
Pau-brasil trees
○
Brazilian Atlantic Forest
○
Long history with humans
•
Current issue: technology, transportation and human population size
•
Before: mix of large and small predators, diverse plant community, diverse
songbird community, few large herbivores
○
After top carnivore removal: large predators absent, small predators
dominant, simplified plant community, lower songbird diversity, numerous
large herbivores
○
Trophic cascades occur when predators in a food web suppress the
abundance or alter the behavior of their prey, thereby releasing the next
lower trophic level from predation (or herbivory if the intermediate trophic
level is a herbivore)
○
Trophic cascade:
•
Transition in landings from long-lived, high trophic level, piscivorous
bottom fish --> short-lived, low trophic level invertebrates and
planktivorous pelagic fish
○
Leads at first to increasing catches then to a phase transition associated
with stagnating or declining catches
○
Present exploitation patterns are unsustainable
○
Fishing down marine food webs:
•
Abundances of great sharks that consume other elasmobranchs fell -->
increased prey species in coastal northwest Atlantic ecosystems
○
Cownose ray --> enhanced predation on bay scallop terminated scallop
fishery
○
Top-down effects may be a predictable consequence of eliminated entire
functional groups of predators
○
Cascading effects of the loss of apex predatory sharks from a coastal ocean:
•
Without predatory fish: prey fish increase --> zoo plankton decline -->
algae increase (algae blooms)
○
Consequences of trophic collapse:
•
Declines in perch and pike --> increase in smaller fish --> algal blooms
○
When predators were intact -10% chance of algal blooms (vs. 50%
without predatory fish)
○
Overfishing linked to algal blooms:
•
Over-exploitation:
Why do we still over-exploit?
○
Are there solutions to this problem?
○
Problem: if there are only so many resources…
•
Common -a piece of land often owned by one person/community, but over
which others can exercise certain traditional rights (such as allowing their
livestock to graze upon it)
○
"multiple individuals acting independently in their own self-interest
ultimately destroy a shared limited resource even where it is clear that it is
not in anyone's long term interest for this to happen"
○
*see prisoners dilemma
○
Land users cannot be relied upon to make rationale decisions, even if
its in their own best interest
!
Solution: strict management of global common goods via increased
government involvement and/or international regulation bodies
!
Hardin:
○
The tragedy of the commons:
•
Bolivian mahogany
○
Housing markets
!
Logging costs
!
DBH (diameter) of the trees, a function of logging frequency, growth
rates and site conditions
!
Value fluctuates in concordance with:
○
Optimal solution: timed cutting intervals to maximize DBH, adjust cutting
to the flow of the market, limit the number of loggers, manage regionally
rather than tree-by-tree
○
Actual strategy: law of diminishing returns to the ultimate detriment of the
logger and the tree
○
How it works in real world:
•
*see diagram on slide
○
Boom-and-bust development patterns across amazon deforestation frontier:
•
Competition between sustainable vs. unsustainable interest groups
○
Short-term benefits (political, economic)
○
Poor quality data for management strategies -as with species protection, so
with sustainable harvesting
○
A universal problem:
•
Enormous impacts on target species
○
Confounded by other co-occurring global changes (warming, invasion,
pollution)
○
Consequences:
•
80% biomass reduction in first 15 years of the fishery
○
Compensatory responses of fast-growing harvested species often observed
but temporary
○
Large predatory fish in world's ocean now reduced by 90%
○
Management on present-day data masks longer term trends of decline in
world's fisheries
○
Rapid world-wide depletion of predatory fish communities:
•
Effects: trophic cascade and declines in population size
•
Sustainable Harvesting
Immigration & natality vs. Mortality & emigration
•
Reindeer introduced in 1910 on Pribilof Islands, Alaska
○
4 males and 22 females
○
After 30 years, there are 2000 individuals
○
--> unsustainable: intense over-grazing
○
8 animals left in 1950
○
Exponential growth:
•
Most populations are limited in growth at some carrying capacity (K) -the
maximum population size (density) a habitat can accommodate
○
Early growth is rapid before growth begins to slow
!
Later growth falls to zero (plateaus)
!
Density dependence: growth rate as a function of population size
○
Logistic growth model:
•
Maximum sustainable yield occurs at population size where population can
grow most quickly (steepest part of growth curve)
○
*see sustainable yield curve
○
Sustainable exploitation:
•
Abundance and Change in Populations:
Catch shares slow the race to fish
•
*tragedy of the commons
Yield is independent of population size
○
High-quota line: yield exceeds the population's surplus production
capability (where B>>D) --> ultimately leads to extinction
○
If quota exceeds surplus = extinction
!
Benefit: works if it reduced density dependence
!
MSY line: reasonable but risky due to data limitations (how do you know
when you're in a surplus)
○
Low-quota: crash possible at N1, but sustainability is most likely at N2
○
Constant Quota Exploitation (least effective)1)
Y = E(N) where E is exploitation rate
!
Yield is dependent on population size (good)
○
Quotas tied directly to the size of the population
○
Tends to happen by default as harvest efforts tend to change when yields
are low
○
Reactive (dog chasing own tail)
○
If population reaches tipping point, recovery may not occur
!
Assumes/depends on small populations recovering (doesn't always occur)
○
Proportional Exploitation2)
Take only when carrying capacity is exceeded (population is about to
decline)
○
Yield = number of individuals over carrying capacity
○
Threshold Exploitation (great; rare)3)
Sustainable Exploitation
Often lack adequate information to make models -must estimate
relationships/parameters using coarse methods (bycatch?)
•
*Models often implemented incorporating other functions (such as economic
costs/benefits)
Mustelid (mink, otters, badgers, wolverines, weasels, skunks)
•
Prey: voles, mice, birds, flying squirrels
○
Old growth conifer forests --> habitat loss
•
Range: 10-30km
•
Trapping -almost extinct in 1700s-1800s
•
Today: small population sizes, logging and on-going trapping
•
Protection: varies, illegal to trap in NFLD (sub-species, n=300)
•
Higher % young in growing population --> higher quota next year
○
OMNR marten harvest determined by proportion of young martens in the
population each year
•
Keys: cooperation and data
•
Sustainable Exploitation -Pine Marten
Short term economic (and political) gains
○
Conservation and sustainable management
○
Trade-offs:
•
$billions per year
○
Hundreds of millions of plant and animal specimens
○
International wildlife trait
•
Food, exotic leather goods, wooden musical instruments, timber, tourist curios,
medicines
•
Exploitation is depleting many species
•
Over-exploitation:
International agreement between governments, ensuring that trade does not
threaten survival
•
Covers >30,000 species
•
Voluntary -does not take the place of national laws
•
CITIES -Convention on International Trade in Endangered Species of Wild Fauna and
Flora (1963 by IUCN)
Between 1979-1989, the worldwide demand for ivory caused elephant
populations to decline to dangerously low levels
•
1977 -1.3 million
•
1997 -600,000
•
Value fell from $90 to $1.35 per pound on the black market
○
1989 -CITIES banned commercial trade of ivory
•
1996 estimate = 580,000
○
After 1989, the elephant population declined only by 20,000
•
Increased conflict between farmers and elephants as suitable habitat shrank
○
"sustainable" culling -approved by IUCN
○
BUT, no ivory collected from culled animals (or from poached animals)
could be sold
○
Zimbabwe, Namibia, Kenya and Botswana: $8 billion dollars worth of
surplus ivory
○
Kenya set fire to huge stockpile of ivory
!
The four nations saw themselves as victims of the skewed viewpoint of
western countries, which dominate CITIES decisions
○
But international conservation donations plummeted
•
Big battle brewing over elephants at CITIES meeting
○
In 1997, CITIES partially lifts trade sanctions
•
Appetite for ivory has again increased (China, US and Japan)
○
More elephants are now killed than before ban (<450,000)
○
8% of African elephants are now being poached every year
○
Risk of extinction by 2020
○
Today…
•
Case Study: African Elephant
Population Viability Analysis
Saturday,*March*25,*2017
11:37*AM
Survival -typically refers to remaining in a stage (age) class
•
Growth -typically refers to going from one stage class to another
•
Reproduction -typically refers to number of offspring per individual
(usually female)
•
Like most demographic analyses, PVAs focus on key birth and death processes,
acknowledging that not all have equal importance for population growth
•
Vital Rates:
Total population size
•
Brood size
•
Proportion of young
•
*key issue: these data are 'relatively' easy to collect
Demography (what can be measured):
Vital rates determine rate of population growth
•
Population size at time 't' is Nt
•
Nt+1 = (lambda)*Nt
•
>1 -population is growing
•
<1 -population is declining
•
=1 -population is stable
•
Lambda -describes the annual population growth rate
•
For some species, estimate lambda = Nt+1 / Nt
•
Estimating Population Growth:
If population growth was the same every year, prediction would be easy but
spatial variation among populations is also present
•
Variation in population growth:
Model simulations only differing by SD
•
Starting size N0=1000
•
Message: larger SD --> wider range of population outcomes after 50 years
•
Population Growth and Prediction:
Management actions can be determined based on information about which life
stages are most important for population growth
•
Trampling of eggs and hatchlings on beaches
!
Drowning of adult turtles in fishing nets
!
Need to determined which of two major threats to logger head turtles is
most important
•
Matrix population model: see slide
•
Reproductive adults were most important stage
!
Efforts aimed at saving eggs and hatchlings would not reverse
population declines even if they were 100% effective
!
PVAs using population data determined the contributions of different life
stages to population growth:
•
Putting turtle excluder devices in fishing nets to prevent drowning would
produce recovery even if it didn’t eliminate all mortality
•
Crouse et al. and Crowder et al. used PVAs to assist with management of
threatened logger head turtles in southeastern US
•
Identifying Key Life Stages:
27 million tons annually (conservative estimate)
•
Long-lived species (albatross, sea turtle)
•
Low absolute rates of bycatch X huge number of fishers = 10,000 black-
footed Albatross per year in north Pacific
•
Fishing Bycatch: 1/3 -1/4 of all catch
•
5:1 ratio of bycatch:shrimp
•
70,000 bycatch individuals discarded per night in Australian prawn fishery
•
Shrimp Trawling (the worst!!!)
•
Sustainable Harvesting:
Feb 2003: National Marine Fisheries Service (NMFS) issues regulations
requiring the US shrimp trawling fleet to install larger turtle excluder device
(TED) openings
•
Allows turtles to escape while sending shrimp to a pocket at end of net
•
TED: escape hatch near end of shrimp net
•
Existing TEDs are too small for large sea turtles
•
The rule mandates the use of TEDs designed to better protect all sea turtle size
classes while having the least economic impact on the shrimp fishery
•
Shrimp trawling is the single largest documented source of sea turtle mortality in
US
•
Sustainable Exploitation: Proposed TED rule would better protect sea turtles
Doing a lot with a little -data limitations
1.
A little variation in reproductive success can have huge impacts on population
growth
2.
Not all life stages are equally important for population growth3.
Putting it all together for conservation -managing for population growth with
limited data
4.
Recall: PVAs
Number of juveniles (Jt) = Nt*Pjt
•
Successfully breeding adults (Abt) = 2*[(Jt)/(Bt)]
•
Number of 2nd year birds (It) = (Jt-1)*(St-1)
•
Potential breeding adults (Apt) = (Nt) -(Jt) -(It)
•
Breeding ratio (Rt) = (Abt)/(Apt)
•
Productivity (Ft) = (Jt)/(Apt)
•
Survival Rates (St) = [(Nt+1) -(Jt+1)] /(Nt)
•
Demography: if we know Nt, Bt and Pjt, we can infer:
Imagine population where Nt+1 = (lambda), and lambda=0.86 with prob 1/2(half
females) and lambda=1.16 with prob 1/2 -within a given year
•
Arithmetic mean of the two lambdas = 1.01 -deterministic (nonrandom) growth
•
N(500) = (100)(1.01^500) = 14,477
•
If you start with 100 individuals and population grows for 500 generations…
•
But population growth is subject to stochasticity (random variation)
•
Now imagine same population (100 individuals growing for 500 generations) but
grow rates vary stochastically either 1.16 or 0.86 among years
•
N(500) = (100) [ (1.16^250) * (0.86^250) ] = 54.8
•
So with both growing rates about equally likely from one year to the next then
population size after 500 generations is….
•
Larger s.d. = wider range of population outcomes
•
Therefore, adding variation to population growth (lambda) usually reduces
population growth
•
Variation in Population Growth:
However, the lack of high-quality data derived from long-term studies, and
uncertainty in model parameters and/or structure, often limit the use of
population models to only a few species of conservation concern
•
The ideal conservation planning approach would enable decision-makers to use
PVAs to assess the effects of management strategies and threats on all species at
the landscape level
•
One of the best options to quantitatively measure the benefits of alternative
conservation actions on the persistence of multiple species is to estimate
the risk of extinction faced by each species using PVA
•
An important shortcoming of the use of population viability analyses is
that they require extensive high quality data derived from long-term studies
and the effect of the conservation actions is generally a guess
•
Conserving biodiversity within limited budgets requires allocating resources to
actions that provide the highest return on investment
•
Selecting reserves in a network that maximizes the viability of one or more
species, communities, or ecosystems
•
Protected area design: optimization
•
Source/sink --> limit number of sinks (D>B)
•
White holes
•
Meta-populations
•
Allee effects
•
Habitat
•
Dangerous edges
•
Extinction debt
•
Sampling effect
•
SLOSS
•
How are each of these relevant for reserve design optimization?
•
Small reserve scenario -metapopulation dynamics were stimulated for
current conditions in which populations are constrained and managed
within individual, fenced, protected areas
i)
Big reserve scenarioii)
Small and Big connectediii)
Big and connectediv)
Bigger and connected, but cheapv)
Biggest reserve scenario vi)
Six scenarios: population viability analysis was performed under six reserve
scenarios, which were developed according to current constraints and future
management opportunities in the study area
•
"Creating Larger and Better Connected Protected Areas Enhances the Persistence of
Big Game Species in the Maputaland-Pondoland-Albany Biodiversity Hotspot"
--> small overlap between protected areas and hot-spots
Population Size
○
Brood Size
○
Proportion of juveniles
○
You’ve been hired to write a recovery plan for the recently listed Woodland
Caribou in northern Ontario -what minimum population data would you need for
a PVA?
1.
N after 10 years in east =(.76^5)(1.34^5)*1000=1095
○
N after 10 years in west = (0.97^5)(1.03^5)*500 = 497
○
You find demographic differences between eastern and western populations.
Eastern populations are twice as large (N=1000). In the west lambda over 10
generations ranges between 0.97 -1.03, whereas eastern populations have a
similar average range between 0.76-1.34. Describe the expected general
differences in population performance between the two populations. Why does
this happen?
2.
This can result in inbreeding, as the number of females decrease
!
Population of females is declining --> total population will not persist
(without a way to reproduce)
○
In east: N after 10 years = (0.57^7.5)(2.12^2.5)*1000=98 (VS 1095)
○
In eastern populations, you find that 75% of the females have a lambda of 0.57
while the rest are highly successful over 10 year period (lambda=2.12). How
does this change the growth projections?
3.
Practice Question:
Occurs when the harvest rate of any given population exceeds its natural
replacement rate, either through reproduction alone in closed populations or
through both reproduction and immigration from other populations
•
Third most important driver of freshwater fish extinction (habitat loss and
degradation have high impacts)
•
Forms: commercial harvests, hunting, fishing
•
Direct and indirect affect on biodiversity (e.g. food webs)
•
Populations are already weakened by climate change
!
Transition into Holocene
○
Ex. Ginseng
!
Ex. Carolinian parakeet -harvested for 1800 fashion (now extinct)
!
Over-exploitation of trees, medicinal plants and animals for their fur still
have echoing impacts today
○
Formed huge stands in forests along 3000km of Brazilian coast line
!
Source of red dye and hardwood
!
1500-1875: over-exploitation (economically extinct)
!
Only found in arboretums and a few protected areas
!
Message: highly abundant species can be as vulnerable as rare
species
!
Pau-brasil trees
○
Brazilian Atlantic Forest
○
Long history with humans
•
Current issue: technology, transportation and human population size
•
Before: mix of large and small predators, diverse plant community, diverse
songbird community, few large herbivores
○
After top carnivore removal: large predators absent, small predators
dominant, simplified plant community, lower songbird diversity, numerous
large herbivores
○
Trophic cascades occur when predators in a food web suppress the
abundance or alter the behavior of their prey, thereby releasing the next
lower trophic level from predation (or herbivory if the intermediate trophic
level is a herbivore)
○
Trophic cascade:
•
Transition in landings from long-lived, high trophic level, piscivorous
bottom fish --> short-lived, low trophic level invertebrates and
planktivorous pelagic fish
○
Leads at first to increasing catches then to a phase transition associated
with stagnating or declining catches
○
Present exploitation patterns are unsustainable
○
Fishing down marine food webs:
•
Abundances of great sharks that consume other elasmobranchs fell -->
increased prey species in coastal northwest Atlantic ecosystems
○
Cownose ray --> enhanced predation on bay scallop terminated scallop
fishery
○
Top-down effects may be a predictable consequence of eliminated entire
functional groups of predators
○
Cascading effects of the loss of apex predatory sharks from a coastal ocean:
•
Without predatory fish: prey fish increase --> zoo plankton decline -->
algae increase (algae blooms)
○
Consequences of trophic collapse:
•
Declines in perch and pike --> increase in smaller fish --> algal blooms
○
When predators were intact -10% chance of algal blooms (vs. 50%
without predatory fish)
○
Overfishing linked to algal blooms:
•
Over-exploitation:
Why do we still over-exploit?
○
Are there solutions to this problem?
○
Problem: if there are only so many resources…
•
Common -a piece of land often owned by one person/community, but over
which others can exercise certain traditional rights (such as allowing their
livestock to graze upon it)
○
"multiple individuals acting independently in their own self-interest
ultimately destroy a shared limited resource even where it is clear that it is
not in anyone's long term interest for this to happen"
○
*see prisoners dilemma
○
Land users cannot be relied upon to make rationale decisions, even if
its in their own best interest
!
Solution: strict management of global common goods via increased
government involvement and/or international regulation bodies
!
Hardin:
○
The tragedy of the commons:
•
Bolivian mahogany
○
Housing markets
!
Logging costs
!
DBH (diameter) of the trees, a function of logging frequency, growth
rates and site conditions
!
Value fluctuates in concordance with:
○
Optimal solution: timed cutting intervals to maximize DBH, adjust cutting
to the flow of the market, limit the number of loggers, manage regionally
rather than tree-by-tree
○
Actual strategy: law of diminishing returns to the ultimate detriment of the
logger and the tree
○
How it works in real world:
•
*see diagram on slide
○
Boom-and-bust development patterns across amazon deforestation frontier:
•
Competition between sustainable vs. unsustainable interest groups
○
Short-term benefits (political, economic)
○
Poor quality data for management strategies -as with species protection, so
with sustainable harvesting
○
A universal problem:
•
Enormous impacts on target species
○
Confounded by other co-occurring global changes (warming, invasion,
pollution)
○
Consequences:
•
80% biomass reduction in first 15 years of the fishery
○
Compensatory responses of fast-growing harvested species often observed
but temporary
○
Large predatory fish in world's ocean now reduced by 90%
○
Management on present-day data masks longer term trends of decline in
world's fisheries
○
Rapid world-wide depletion of predatory fish communities:
•
Effects: trophic cascade and declines in population size
•
Sustainable Harvesting
Immigration & natality vs. Mortality & emigration
•
Reindeer introduced in 1910 on Pribilof Islands, Alaska
○
4 males and 22 females
○
After 30 years, there are 2000 individuals
○
--> unsustainable: intense over-grazing
○
8 animals left in 1950
○
Exponential growth:
•
Most populations are limited in growth at some carrying capacity (K) -the
maximum population size (density) a habitat can accommodate
○
Early growth is rapid before growth begins to slow
!
Later growth falls to zero (plateaus)
!
Density dependence: growth rate as a function of population size
○
Logistic growth model:
•
Maximum sustainable yield occurs at population size where population can
grow most quickly (steepest part of growth curve)
○
*see sustainable yield curve
○
Sustainable exploitation:
•
Abundance and Change in Populations:
Catch shares slow the race to fish
•
*tragedy of the commons
Yield is independent of population size
○
High-quota line: yield exceeds the population's surplus production
capability (where B>>D) --> ultimately leads to extinction
○
If quota exceeds surplus = extinction
!
Benefit: works if it reduced density dependence
!
MSY line: reasonable but risky due to data limitations (how do you know
when you're in a surplus)
○
Low-quota: crash possible at N1, but sustainability is most likely at N2
○
Constant Quota Exploitation (least effective)1)
Y = E(N) where E is exploitation rate
!
Yield is dependent on population size (good)
○
Quotas tied directly to the size of the population
○
Tends to happen by default as harvest efforts tend to change when yields
are low
○
Reactive (dog chasing own tail)
○
If population reaches tipping point, recovery may not occur
!
Assumes/depends on small populations recovering (doesn't always occur)
○
Proportional Exploitation2)
Take only when carrying capacity is exceeded (population is about to
decline)
○
Yield = number of individuals over carrying capacity
○
Threshold Exploitation (great; rare)3)
Sustainable Exploitation
Often lack adequate information to make models -must estimate
relationships/parameters using coarse methods (bycatch?)
•
*Models often implemented incorporating other functions (such as economic
costs/benefits)
Mustelid (mink, otters, badgers, wolverines, weasels, skunks)
•
Prey: voles, mice, birds, flying squirrels
○
Old growth conifer forests --> habitat loss
•
Range: 10-30km
•
Trapping -almost extinct in 1700s-1800s
•
Today: small population sizes, logging and on-going trapping
•
Protection: varies, illegal to trap in NFLD (sub-species, n=300)
•
Higher % young in growing population --> higher quota next year
○
OMNR marten harvest determined by proportion of young martens in the
population each year
•
Keys: cooperation and data
•
Sustainable Exploitation -Pine Marten
Short term economic (and political) gains
○
Conservation and sustainable management
○
Trade-offs:
•
$billions per year
○
Hundreds of millions of plant and animal specimens
○
International wildlife trait
•
Food, exotic leather goods, wooden musical instruments, timber, tourist curios,
medicines
•
Exploitation is depleting many species
•
Over-exploitation:
International agreement between governments, ensuring that trade does not
threaten survival
•
Covers >30,000 species
•
Voluntary -does not take the place of national laws
•
CITIES -Convention on International Trade in Endangered Species of Wild Fauna and
Flora (1963 by IUCN)
Between 1979-1989, the worldwide demand for ivory caused elephant
populations to decline to dangerously low levels
•
1977 -1.3 million
•
1997 -600,000
•
Value fell from $90 to $1.35 per pound on the black market
○
1989 -CITIES banned commercial trade of ivory
•
1996 estimate = 580,000
○
After 1989, the elephant population declined only by 20,000
•
Increased conflict between farmers and elephants as suitable habitat shrank
○
"sustainable" culling -approved by IUCN
○
BUT, no ivory collected from culled animals (or from poached animals)
could be sold
○
Zimbabwe, Namibia, Kenya and Botswana: $8 billion dollars worth of
surplus ivory
○
Kenya set fire to huge stockpile of ivory
!
The four nations saw themselves as victims of the skewed viewpoint of
western countries, which dominate CITIES decisions
○
But international conservation donations plummeted
•
Big battle brewing over elephants at CITIES meeting
○
In 1997, CITIES partially lifts trade sanctions
•
Appetite for ivory has again increased (China, US and Japan)
○
More elephants are now killed than before ban (<450,000)
○
8% of African elephants are now being poached every year
○
Risk of extinction by 2020
○
Today…
•
Case Study: African Elephant
Population Viability Analysis
Saturday,*March*25,*2017 11:37*AM
Survival -typically refers to remaining in a stage (age) class
•
Growth -typically refers to going from one stage class to another
•
Reproduction -typically refers to number of offspring per individual
(usually female)
•
Like most demographic analyses, PVAs focus on key birth and death processes,
acknowledging that not all have equal importance for population growth
•
Vital Rates:
Total population size
•
Brood size
•
Proportion of young
•
*key issue: these data are 'relatively' easy to collect
Demography (what can be measured):
Vital rates determine rate of population growth
•
Population size at time 't' is Nt
•
Nt+1 = (lambda)*Nt
•
>1 -population is growing
•
<1 -population is declining
•
=1 -population is stable
•
Lambda -describes the annual population growth rate
•
For some species, estimate lambda = Nt+1 / Nt
•
Estimating Population Growth:
If population growth was the same every year, prediction would be easy but
spatial variation among populations is also present
•
Variation in population growth:
Model simulations only differing by SD
•
Starting size N0=1000
•
Message: larger SD --> wider range of population outcomes after 50 years
•
Population Growth and Prediction:
Management actions can be determined based on information about which life
stages are most important for population growth
•
Trampling of eggs and hatchlings on beaches
!
Drowning of adult turtles in fishing nets
!
Need to determined which of two major threats to logger head turtles is
most important
•
Matrix population model: see slide
•
Reproductive adults were most important stage
!
Efforts aimed at saving eggs and hatchlings would not reverse
population declines even if they were 100% effective
!
PVAs using population data determined the contributions of different life
stages to population growth:
•
Putting turtle excluder devices in fishing nets to prevent drowning would
produce recovery even if it didn’t eliminate all mortality
•
Crouse et al. and Crowder et al. used PVAs to assist with management of
threatened logger head turtles in southeastern US
•
Identifying Key Life Stages:
27 million tons annually (conservative estimate)
•
Long-lived species (albatross, sea turtle)
•
Low absolute rates of bycatch X huge number of fishers = 10,000 black-
footed Albatross per year in north Pacific
•
Fishing Bycatch: 1/3 -1/4 of all catch
•
5:1 ratio of bycatch:shrimp
•
70,000 bycatch individuals discarded per night in Australian prawn fishery
•
Shrimp Trawling (the worst!!!)
•
Sustainable Harvesting:
Feb 2003: National Marine Fisheries Service (NMFS) issues regulations
requiring the US shrimp trawling fleet to install larger turtle excluder device
(TED) openings
•
Allows turtles to escape while sending shrimp to a pocket at end of net
•
TED: escape hatch near end of shrimp net
•
Existing TEDs are too small for large sea turtles
•
The rule mandates the use of TEDs designed to better protect all sea turtle size
classes while having the least economic impact on the shrimp fishery
•
Shrimp trawling is the single largest documented source of sea turtle mortality in
US
•
Sustainable Exploitation: Proposed TED rule would better protect sea turtles
Doing a lot with a little -data limitations1.
A little variation in reproductive success can have huge impacts on population
growth
2.
Not all life stages are equally important for population growth
3.
Putting it all together for conservation -managing for population growth with
limited data
4.
Recall: PVAs
Number of juveniles (Jt) = Nt*Pjt
•
Successfully breeding adults (Abt) = 2*[(Jt)/(Bt)]
•
Number of 2nd year birds (It) = (Jt-1)*(St-1)
•
Potential breeding adults (Apt) = (Nt) -(Jt) -(It)
•
Breeding ratio (Rt) = (Abt)/(Apt)
•
Productivity (Ft) = (Jt)/(Apt)
•
Survival Rates (St) = [(Nt+1) -(Jt+1)] /(Nt)
•
Demography: if we know Nt, Bt and Pjt, we can infer:
Imagine population where Nt+1 = (lambda), and lambda=0.86 with prob 1/2(half
females) and lambda=1.16 with prob 1/2 -within a given year
•
Arithmetic mean of the two lambdas = 1.01 -deterministic (nonrandom) growth
•
N(500) = (100)(1.01^500) = 14,477
•
If you start with 100 individuals and population grows for 500 generations…
•
But population growth is subject to stochasticity (random variation)
•
Now imagine same population (100 individuals growing for 500 generations) but
grow rates vary stochastically either 1.16 or 0.86 among years
•
N(500) = (100) [ (1.16^250) * (0.86^250) ] = 54.8
•
So with both growing rates about equally likely from one year to the next then
population size after 500 generations is….
•
Larger s.d. = wider range of population outcomes
•
Therefore, adding variation to population growth (lambda) usually reduces
population growth
•
Variation in Population Growth:
However, the lack of high-quality data derived from long-term studies, and
uncertainty in model parameters and/or structure, often limit the use of
population models to only a few species of conservation concern
•
The ideal conservation planning approach would enable decision-makers to use
PVAs to assess the effects of management strategies and threats on all species at
the landscape level
•
One of the best options to quantitatively measure the benefits of alternative
conservation actions on the persistence of multiple species is to estimate
the risk of extinction faced by each species using PVA
•
An important shortcoming of the use of population viability analyses is
that they require extensive high quality data derived from long-term studies
and the effect of the conservation actions is generally a guess
•
Conserving biodiversity within limited budgets requires allocating resources to
actions that provide the highest return on investment
•
Selecting reserves in a network that maximizes the viability of one or more
species, communities, or ecosystems
•
Protected area design: optimization
•
Source/sink --> limit number of sinks (D>B)
•
White holes
•
Meta-populations
•
Allee effects
•
Habitat
•
Dangerous edges
•
Extinction debt
•
Sampling effect
•
SLOSS
•
How are each of these relevant for reserve design optimization?
•
Small reserve scenario -metapopulation dynamics were stimulated for
current conditions in which populations are constrained and managed
within individual, fenced, protected areas
i)
Big reserve scenarioii)
Small and Big connectediii)
Big and connectediv)
Bigger and connected, but cheapv)
Biggest reserve scenario vi)
Six scenarios: population viability analysis was performed under six reserve
scenarios, which were developed according to current constraints and future
management opportunities in the study area
•
"Creating Larger and Better Connected Protected Areas Enhances the Persistence of
Big Game Species in the Maputaland-Pondoland-Albany Biodiversity Hotspot"
--> small overlap between protected areas and hot-spots
Population Size
○
Brood Size
○
Proportion of juveniles
○
You’ve been hired to write a recovery plan for the recently listed Woodland
Caribou in northern Ontario -what minimum population data would you need for
a PVA?
1.
N after 10 years in east =(.76^5)(1.34^5)*1000=1095
○
N after 10 years in west = (0.97^5)(1.03^5)*500 = 497
○
You find demographic differences between eastern and western populations.
Eastern populations are twice as large (N=1000). In the west lambda over 10
generations ranges between 0.97 -1.03, whereas eastern populations have a
similar average range between 0.76-1.34. Describe the expected general
differences in population performance between the two populations. Why does
this happen?
2.
This can result in inbreeding, as the number of females decrease
!
Population of females is declining --> total population will not persist
(without a way to reproduce)
○
In east: N after 10 years = (0.57^7.5)(2.12^2.5)*1000=98 (VS 1095)
○
In eastern populations, you find that 75% of the females have a lambda of 0.57
while the rest are highly successful over 10 year period (lambda=2.12). How
does this change the growth projections?
3.
Practice Question:
Occurs when the harvest rate of any given population exceeds its natural
replacement rate, either through reproduction alone in closed populations or
through both reproduction and immigration from other populations
•
Third most important driver of freshwater fish extinction (habitat loss and
degradation have high impacts)
•
Forms: commercial harvests, hunting, fishing
•
Direct and indirect affect on biodiversity (e.g. food webs)
•
Populations are already weakened by climate change
!
Transition into Holocene
○
Ex. Ginseng
!
Ex. Carolinian parakeet -harvested for 1800 fashion (now extinct)
!
Over-exploitation of trees, medicinal plants and animals for their fur still
have echoing impacts today
○
Formed huge stands in forests along 3000km of Brazilian coast line
!
Source of red dye and hardwood
!
1500-1875: over-exploitation (economically extinct)
!
Only found in arboretums and a few protected areas
!
Message: highly abundant species can be as vulnerable as rare
species
!
Pau-brasil trees
○
Brazilian Atlantic Forest
○
Long history with humans
•
Current issue: technology, transportation and human population size
•
Before: mix of large and small predators, diverse plant community, diverse
songbird community, few large herbivores
○
After top carnivore removal: large predators absent, small predators
dominant, simplified plant community, lower songbird diversity, numerous
large herbivores
○
Trophic cascades occur when predators in a food web suppress the
abundance or alter the behavior of their prey, thereby releasing the next
lower trophic level from predation (or herbivory if the intermediate trophic
level is a herbivore)
○
Trophic cascade:
•
Transition in landings from long-lived, high trophic level, piscivorous
bottom fish --> short-lived, low trophic level invertebrates and
planktivorous pelagic fish
○
Leads at first to increasing catches then to a phase transition associated
with stagnating or declining catches
○
Present exploitation patterns are unsustainable
○
Fishing down marine food webs:
•
Abundances of great sharks that consume other elasmobranchs fell -->
increased prey species in coastal northwest Atlantic ecosystems
○
Cownose ray --> enhanced predation on bay scallop terminated scallop
fishery
○
Top-down effects may be a predictable consequence of eliminated entire
functional groups of predators
○
Cascading effects of the loss of apex predatory sharks from a coastal ocean:
•
Without predatory fish: prey fish increase --> zoo plankton decline -->
algae increase (algae blooms)
○
Consequences of trophic collapse:
•
Declines in perch and pike --> increase in smaller fish --> algal blooms
○
When predators were intact -10% chance of algal blooms (vs. 50%
without predatory fish)
○
Overfishing linked to algal blooms:
•
Over-exploitation:
Why do we still over-exploit?
○
Are there solutions to this problem?
○
Problem: if there are only so many resources…
•
Common -a piece of land often owned by one person/community, but over
which others can exercise certain traditional rights (such as allowing their
livestock to graze upon it)
○
"multiple individuals acting independently in their own self-interest
ultimately destroy a shared limited resource even where it is clear that it is
not in anyone's long term interest for this to happen"
○
*see prisoners dilemma
○
Land users cannot be relied upon to make rationale decisions, even if
its in their own best interest
!
Solution: strict management of global common goods via increased
government involvement and/or international regulation bodies
!
Hardin:
○
The tragedy of the commons:
•
Bolivian mahogany
○
Housing markets
!
Logging costs
!
DBH (diameter) of the trees, a function of logging frequency, growth
rates and site conditions
!
Value fluctuates in concordance with:
○
Optimal solution: timed cutting intervals to maximize DBH, adjust cutting
to the flow of the market, limit the number of loggers, manage regionally
rather than tree-by-tree
○
Actual strategy: law of diminishing returns to the ultimate detriment of the
logger and the tree
○
How it works in real world:
•
*see diagram on slide
○
Boom-and-bust development patterns across amazon deforestation frontier:
•
Competition between sustainable vs. unsustainable interest groups
○
Short-term benefits (political, economic)
○
Poor quality data for management strategies -as with species protection, so
with sustainable harvesting
○
A universal problem:
•
Enormous impacts on target species
○
Confounded by other co-occurring global changes (warming, invasion,
pollution)
○
Consequences:
•
80% biomass reduction in first 15 years of the fishery
○
Compensatory responses of fast-growing harvested species often observed
but temporary
○
Large predatory fish in world's ocean now reduced by 90%
○
Management on present-day data masks longer term trends of decline in
world's fisheries
○
Rapid world-wide depletion of predatory fish communities:
•
Effects: trophic cascade and declines in population size
•
Sustainable Harvesting
Immigration & natality vs. Mortality & emigration
•
Reindeer introduced in 1910 on Pribilof Islands, Alaska
○
4 males and 22 females
○
After 30 years, there are 2000 individuals
○
--> unsustainable: intense over-grazing
○
8 animals left in 1950
○
Exponential growth:
•
Most populations are limited in growth at some carrying capacity (K) -the
maximum population size (density) a habitat can accommodate
○
Early growth is rapid before growth begins to slow
!
Later growth falls to zero (plateaus)
!
Density dependence: growth rate as a function of population size
○
Logistic growth model:
•
Maximum sustainable yield occurs at population size where population can
grow most quickly (steepest part of growth curve)
○
*see sustainable yield curve
○
Sustainable exploitation:
•
Abundance and Change in Populations:
Catch shares slow the race to fish
•
*tragedy of the commons
Yield is independent of population size
○
High-quota line: yield exceeds the population's surplus production
capability (where B>>D) --> ultimately leads to extinction
○
If quota exceeds surplus = extinction
!
Benefit: works if it reduced density dependence
!
MSY line: reasonable but risky due to data limitations (how do you know
when you're in a surplus)
○
Low-quota: crash possible at N1, but sustainability is most likely at N2
○
Constant Quota Exploitation (least effective)1)
Y = E(N) where E is exploitation rate
!
Yield is dependent on population size (good)
○
Quotas tied directly to the size of the population
○
Tends to happen by default as harvest efforts tend to change when yields
are low
○
Reactive (dog chasing own tail)
○
If population reaches tipping point, recovery may not occur
!
Assumes/depends on small populations recovering (doesn't always occur)
○
Proportional Exploitation2)
Take only when carrying capacity is exceeded (population is about to
decline)
○
Yield = number of individuals over carrying capacity
○
Threshold Exploitation (great; rare)3)
Sustainable Exploitation
Often lack adequate information to make models -must estimate
relationships/parameters using coarse methods (bycatch?)
•
*Models often implemented incorporating other functions (such as economic
costs/benefits)
Mustelid (mink, otters, badgers, wolverines, weasels, skunks)
•
Prey: voles, mice, birds, flying squirrels
○
Old growth conifer forests --> habitat loss
•
Range: 10-30km
•
Trapping -almost extinct in 1700s-1800s
•
Today: small population sizes, logging and on-going trapping
•
Protection: varies, illegal to trap in NFLD (sub-species, n=300)
•
Higher % young in growing population --> higher quota next year
○
OMNR marten harvest determined by proportion of young martens in the
population each year
•
Keys: cooperation and data
•
Sustainable Exploitation -Pine Marten
Short term economic (and political) gains
○
Conservation and sustainable management
○
Trade-offs:
•
$billions per year
○
Hundreds of millions of plant and animal specimens
○
International wildlife trait
•
Food, exotic leather goods, wooden musical instruments, timber, tourist curios,
medicines
•
Exploitation is depleting many species
•
Over-exploitation:
International agreement between governments, ensuring that trade does not
threaten survival
•
Covers >30,000 species
•
Voluntary -does not take the place of national laws
•
CITIES -Convention on International Trade in Endangered Species of Wild Fauna and
Flora (1963 by IUCN)
Between 1979-1989, the worldwide demand for ivory caused elephant
populations to decline to dangerously low levels
•
1977 -1.3 million
•
1997 -600,000
•
Value fell from $90 to $1.35 per pound on the black market
○
1989 -CITIES banned commercial trade of ivory
•
1996 estimate = 580,000
○
After 1989, the elephant population declined only by 20,000
•
Increased conflict between farmers and elephants as suitable habitat shrank
○
"sustainable" culling -approved by IUCN
○
BUT, no ivory collected from culled animals (or from poached animals)
could be sold
○
Zimbabwe, Namibia, Kenya and Botswana: $8 billion dollars worth of
surplus ivory
○
Kenya set fire to huge stockpile of ivory
!
The four nations saw themselves as victims of the skewed viewpoint of
western countries, which dominate CITIES decisions
○
But international conservation donations plummeted
•
Big battle brewing over elephants at CITIES meeting
○
In 1997, CITIES partially lifts trade sanctions
•
Appetite for ivory has again increased (China, US and Japan)
○
More elephants are now killed than before ban (<450,000)
○
8% of African elephants are now being poached every year
○
Risk of extinction by 2020
○
Today…
•
Case Study: African Elephant
Population Viability Analysis
Saturday,*March*25,*2017 11:37*AM
Document Summary
Like most demographic analyses, pvas focus on key birth and death processes, acknowledging that not all have equal importance for population growth. Survival - typically refers to remaining in a stage (age) class. Growth - typically refers to going from one stage class to another. Reproduction - typically refers to number of offspring per individual (usually female) *key issue: these data are "relatively" easy to collect. Lambda - describes the annual population growth rate. For some species, estimate lambda = nt+1 / nt. If population growth was the same every year, prediction would be easy but spatial variation among populations is also present. Message: larger sd --> wider range of population outcomes after 50 years. Management actions can be determined based on information about which life. Management actions can be determined based on information about which life stages are most important for population growth.
