exam 2- conservation bio Flashcards
lecture 15: reproductive value
Idealized Survivorship Curves- humans, animals, and shells
humans have a steady max. life span until they are close to 100 years old where the chances of living begin to drop significantly
animals like squirrels have a steady life span expectancy no matter what age they are at
shells’ life span expectancy begins to drop as soon as they are born but when they get to about 20 years they have a higher chance of survival then it drops to zero once again when they are 40+
idealized survivorship curves
a graph showing the number or proportion of individuals surviving to each age for a given species or group (e.g. males or females).
Reproductive Cost
nonreproductive females have a zero chance of annual mortality rate until they reach age 13 where it skyrockets
reproductive females have a 0.15 chance of annual mortality rate from age 3, and at age 4-10 they have an AMR between 0.1 to 0.05, after age 10 the number skyrocket
thus shows that nonreproductive females have a higher chance of living on average than reproductive females
so the cost of reproduction is increased chance of death earlier in life
behavioral cost of reproduction
the behavior/role of clownfish changes in response to the need to be able to reproduce
the role change: the dad becomes the mom and mates with the young…
called mouthing
mouthing
the largest fish is female
second, largest is the reproductive male
then there even smaller ones are waiting (mouthing)
when the female dies the reproductive male becomes a female and the fish that were waiting become the male for the female to reproduce
they become the next thing when they get bigger
for the clown fish, do females or males survive more
females survive more often than male
because males do the mouthing and fanning and they use more energy
for females more eggs, less energy for surviving
what the graph says about brood (family of animals) sizes: for reduced, normal, enlarged
Important Terms for reproductive value
Fecundity
Reproductive Value (RV)- absolute and relative
residual reproductive value (RRV)
Fecundity
the reproductive rate; usually expressed as the number of daughters produced by each female per time
Reproductive Value (RV)
Absolute and relative
a measure of the average influence of an individual of some age on the future size of the population
- absolute reproductive value is the number of offspring an individual is expected to have in their remaining lifetime
- relative reproductive value is the expected remaining reproduction normalized against the expected lifetime reproduction of an individual who was just born
Reproductive Value (RV)
Absolute and relative
a measure of the average influence of an individual of some age on the future size of the population
- absolute reproductive value is the number of offspring an individual is expected to have in their remaining lifetime
- relative reproductive value is the expected remaining reproduction normalized against the expected lifetime reproduction of an individual who was just born
Residual Reproductive Value (RRV)
the number or relative number of offspring expected in the future after the present breeding season (as opposed to “present RV”)
Reproductive Value (RV) is a complex function of age
animals have the highest RV at their first reproduction because they are likely to have more offspring when they have their first one
you can’t also have offspring as soon as your born
chances of reproducing also plummet when they are close to death
Isofitness Curve for Stable Populations
has to do with relative RV
can allow us to look at delayed reproduction
the future probability of having offspring
Delayed Reproduction of isofitness curves
In this population, the most successful strategy is to
delay reproduction
If you calculate RV for every point on the line (residual which is the Y axis + current which is the X axis ), none has a greater value than at the point at which all reproduction is in the future
Optimum for individual or population: the point at which
all reproduction is in the future
Example: An organism just reached sexual maturity but
is not fully grown. Further growth would increase its
ability to survive reproduction and produce more
offspring.
Requires that the organism has a good chance of
survival until the time of reproduction
Semelparity (“the Big Bang”) of is-fitness curves
In this population, the most successful strategy is to
produce all offspring in one event or one short
season
If you calculate RV for every point on the line (residual +
current), none has a greater value than at the point at
which all reproduction is completed
Current reproduction is the largest
Example: An organism just reached sexual maturity but
that organism has a poor chance of survival until the
time of reproduction or poor chance of future
reproduction
Common in situations where the initial costs of
reproduction is high, but once these have been
met, the cost of additional eggs is very low
Iteroparity for isofitness curves
In this population, the most successful strategy is a
mixed strategy to produce some offspring now and
some in the future
If you calculate RV for every point on the line (residual +
current), none has a greater value than at the point at
which the peak is tangent to the largest isofitness
curve it touches
Which reproductive strategy would likely be employed by humans at the ages 12, 25, and 45?
age 12- delayed reproductive value; can have kids but will wait for more growth and maturity
age 25- iteroparity; based on this, human reproduction is iteroparity mixed (age 25)
age 45- semelparity; having all children at the end in a big bang fashion
Which reproductive strategy would likely be employed by sockeye salmon?
semelparity- all at once at the end of their life
helps us understand survivorship and when these organisms are reproducing now or in the future
Estimating Population Size- rarefaction curve
a plot of the number of species against the number of samples. This curve is created by randomly re-sampling the pool of N samples several times and then plotting the average number of species found on each sample.
Estimating Population Size- Mark & Recapture Techniques
are used to estimate the size of a population where it is impractical or impossible to count every individual
Capture a small number of individuals
Put a harmless mark on them
Release them back into the population
After a period of time, capture a new sample of the population and note how many are marked
The percentage of marked individuals should be the same in both the sample and the real population
Estimating Population Size– Mark & Recapture Technique–Lincoln-Petersen Technique
Assumptions:
1. Mark has no impact on survival
2. No effect on the chance of recapture
3. Full mixing of marked and unmarked individuals
4. No age-stage biases (samples are
representative of population demographics)
5. No migration
6. Population size remains approximately stable
during the sampling time
7. Marks on not lost
what can we use to track and count individuals over time
animal sightings and individual morphological features to track and count individuals over time
Need to be paired with sampling effort and sampling location to be effective measures Relies on the ability of the recorder to correctly identify individuals
how can we track and count animals that do not have unique features
For animals that do not have identifiable and unique features, we can also use genetic analysis from noninvasive sampling
Ex: feces contains cells shed from the intestinal lining
- Sampling hair or fur
Use polymerase chain reaction (PCR) technology to amplify small samples of DNA and then use “genetic fingerprinting” techniques to identify individuals
Environmental Stochasticity
Unpredictable events in the environment that primarily result in immediate death or increased survival and may ultimately affect b and i and e
Demographic Stochasticity:
Variation in b and d due to the fact that actual births and deaths have a probabilistic component
They are not constant averages as treated in typical population models.
Ultimately, there may be a cause but often it is hard to discern and overall the processes appear to have random elements.
Population Viability Analysis (PVA)
Quantitative assessment of the probability of the extinction of a population Criteria:
“Good data” — consistent, long-term, accurate, reasonable sampling
Future population growth must resemble its recent past
Population Viability Analysis (PVA)- stochasticity
Including stochasticity is essential for a more realistic analysis, but requires more data
- Highlights the importance of demographic data
- Predictions are more likely to be accurate over the short-term
-Stochasticity can cause a population to go extinct even if it is growing
Minimum Viable Population
-Early application of PVA
-Recent studies suggest that we might not be able to
calculate MVP from models
-The population size above which a species had a
good chance of surviving over some specific time scale
-Initially defined as the smallest isolated population having
a 99% chance of remaining extant for 1,000 years
despite environmental stochasticity
-Currently, often defined as the minimum number of
individuals having a 95% probability of persisting
over 50 or 100 years
-Very useful for targeted conservation efforts to
maintain population level
-Does not take address the fact that a larger number of
individuals may still be required for that species to
perform its functional role in a biological community
Disturbance
a temporary change in environmental conditions that act to disrupt stable ecosystems and alter the structure and/or function of a habitat
can be natural (natural disturbances) or people (anthropogenic disturbances)
D Disturbances
cause a shift in mortality rates (i.e. death)
D for death
example: drought
B Disturbances
cause a shift in reproductive rates (i.e. birth)
B for birth
example: shift in sex ratio
K Disturbances
cause a shift in carrying capacity (K)
K for carrying capacity
shift in food resources or reduce size of habitat
Intermediate Disturbance Hypothesis
states that the highest levels of diversity should theoretically occur at intermediate disturbance levels
Low disturbance
competitive exclusion increases
Intermediate disturbance
disturbance decreases competitive advantage and allows species that can survive at both early and late successional stages to coexist
High disturbance
less diversity due to movement and loss of species
Fires are destructive disturbances that can have diverse impacts:
(1) cause successional processes to occur in some environments
(2) act as a normal small-scale disturbance in some environments (ex: grasslands and fire cycles)
(3) can be used as a form of management in some species
Succession
refers to the change in species composition over time after a disturbance in a predictable manner.
succession pattern is determined by
the physical environment (rainfall, temperature, humidity)
* soil characteristics
* other species and the rates at which they enter the system
Two Types of Succession:
primary and secondary
primary succession
the successional process that occurs after the colonization of a previously uninhabited environment
Secondary succession
the successional process that occurs after a disturbance disrupts an already existing biotic community
stages of succession example
eroding rocks, nutrient deposition which then form bushes, flower
Succession timeline
The timeline for forest succession can be over 100 years. In the United States, monitoring for ecological restoration projects typically is funded for five or less years.
What makes succession possible – why do we move from one stage to the next?
positive feedback loop and complementarian
Why do climaxes exist?
carrying capacity or have more functions occuring
Why is succession important to conservation biologists?
-because we can look into what the management will look like, maybe you care about fire prevention
-what can con. bio. learn from this is learn from the resilience
Resilience
the ability of an ecosystem to maintain its normal patterns of nutrient cycling and biomass production after being subjected to damage caused by ecological disturbance
Individual resilience
ability of individuals or structures to tolerate or persist through disturbance, allowing the system to return to its pre- disturbance state relatively unchanged (persistence)
Population
re-establishment of the pre-disturbance population following the mortality of the original individuals, through recruitment or colonization (recovery)
Community
as the magnitude of disturbance and interacting chronic stressors increase, both persistence and recovery processes can fail, and the system reorganizes into an alternative state
Stability
local and global
- Local stability
stable against minor or short-term disturbances
Global stability
an ecosystem/community that is highly resistant to change in terms of its community structure
and energy/nutrient flows
Constancy
resistance
inertia
resilience
elasticity
amplitude
Resistance
a descriptor of the ability of a system to remain largely the same in the face of disturbance
- Inertia (persistence)
more inertial systems change less in response to perturbations
Resilience
ability to recover and/or rate of recovery from a disturbance
- Elasticity
the speed with which a system returns to a close approximation of the pre-disturbance state
- Amplitude is a measure of
the initial disturbance effect and
* degree of return of a disturbed system
Adaptive Capacity
refers to the latent potential of an ecological system (or other complex systems) to respond to disturbances in a manner that alters its resilience to change
high resilience image
the ball is at the lowest valley meaning that it will take a high amount of disturbance to disturbance the system
low resilience image
the ball is at the highest valley meaning that it will take a low amount of disturbance to disturbance the system
Population genetics
refers to the study of the genetic composition of populations
Distributions and changes in genotype and phenotype frequency
In response to processes of natural selection, genetic drift, mutation, and gene flow
Alpha diversity
refers to the mean diversity of species in different sites or habitats within local scales
Generally the size of one ecosystem Variation within the group
diversity within populations
Beta diversity
refers to the extent of change in community composition, or degree of community differentiation, in relation to a complex gradient of environment, or a pattern of environments
Variation between groups
The ratio between regional and local species diversity
diversity between populations
Gamma diversity
is studied at a very large scale (i.e. biome) where species diversity is compared between many ecosystems.
- The total species diversity within a landscape
- For example entire littoral zone
Factors Affecting Genetic Diversity
directed agents
chance agents
others
Directed Agents affecting genetic diversity
selection
migration including outbreeding
inbreeding
chance agents affecting genetic diversity
mutation
genetic drift
other things affecting genetic diversity
founder events- the population is descended from a small number of colonizing ancestors ( - )
bottleneck events- famine, earthquake, fire, other disasters ( - )
Wahlund effect: subdivision into genetically distinct subpopulations (- heterozygosity)
outbreeding
matings between individuals from different populations, subspecies, or species. Outbreeding can result in a decline in reproductive fitness known as outbreeding depression, but this is less common than inbreeding depression.
ex: being born to parents that are not related
inbreeding
occurs when mates are related to each other due to incest, assortative mating, small population size, or population sub-structuring. Inbreeding results in an excess of homozygotes and hence a deficiency of heterozygotes.
genetic drift
variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce.
Dangers of Small Populations- two options
Little new genetic diversity
Rapid loss of old diversity
Little new genetic diversity dangers of small populations
*Mutations are rare
*No gene flow
Rapid loss of old diversity dangers of small populations
*Selection
*Genetic drift/founder effects
*Inbreeding
Allee Effect
refers to the density-
dependent feedback loop where per
capita growth rate declines as population
size (N) declines
results of the Allee effect
Difficulty mate finding
Cooperative hunting suffers
Protection from predators declines
Disrupts social interactions
(courtship displays, communal
rearing of young, etc.)
Isolated small patches of flowers:
Receive less pollen
Produce fewer seeds
Are more likely to go extinct due to
insufficient reproductive success
Extinction Vortex -
refers to the class of the population
models that conservation biologists use to understand the dynamics of extinction
–events that ultimately lead small populations to
become increasingly more vulnerable as they spiral
toward extinction
F Vortex
decrease in N leads to lower heterozygosity,
increasing risk of genetic drift and inbreeding depression
A Vortex
decrease in N leads to greater impacts on genetic
drift, decreasing adaptive potential
R Vortex
disturbance lowers N, leading to more variability
(ex: disruption of sex ratios)
D Vortex
disturbance lowers N, leading to increasingly
fragmented populations
Effective Population Size & Loss of Heterozygosity
- In ideal conditions, N = NE and the proportion of
heterozygotes remains constant.
H0 = initial heterozygosity (set to 1.0)
Ht = heterozygosity at time t.
NE = effective population size
Wahlund Effect
refers
to the reduction of
heterozygosity in a
population caused by
subpopulation structure
–Increase in the frequency
of homozygotes in
subdivided populations
–“Fixed” on one allele:
a change in the gene
pool from a situation
where there are at
At least two variants of a
particular gene
(polymorphism) to a
situation where only
one allele remains
(fixation)
deme
a population of organisms within which the exchange of genes is completely random
all viable mating combinations have the same probability of occurrence
Usually not a closed population
Contributes individuals to neighboring populations Receive immigrants from other populations
Dispersal
is the process through which any movement has the potential to lead to gene flow
- impacts individual fitness as well as population dynamics, population genetics, and species distribution
Immigration of genotypes representative of the central populations acts as a brake on deme differentiation
-Genotypic differences that might build up between demes can be slowed or prevented by migrants that arrive with alleles more characteristic of other demes
-Most gene flow (genetic interchange) occurs between central populations
-less between central and peripheral populations, and usually minimal or no flow between peripheral demes.
Hardy-Weinberg Principle
states that allele and genotype frequencies will remain constant from generation to generation in the absence of other evolutionary influences
hardy-Weinberg conditions
does the HW happen in reality?
No influence of genetic drift, mate choice, assortative mating, natural selection, sexual selection, mutation, gene flow, genetic hitchhiking, population bottleneck, founder effect, and inbreeding
The population is infinitely large
The population is panmictic (randomly breeding)
Because all of these disruptive forces commonly occur in nature, the Hardy-Weinberg equilibrium rarely applies in reality.
panmictic
random breeding
Allele Frequencies
the sum of all allele frequencies is 1 (p+q =1)
Genotype Frequencies
if the allelic frequency is the sum of p + q, then the genotype frequency is the product of the frequency of two alleles [(p+q) x (p+q)] or (p+q)2 = 12
heterozygotes
p= freq(A) = [(2 x #homozygotes) + #heterozygotes] / Total # alleles (2 x N)
FIS:
estimates divergence between the average heterozygosity of individuals in one or more demes as
compared to the expected average heterozygosity for those demes
homozygotes
q = freq(a) = 1 - p
FIS=0
then there is no subpopulation differentiation with respect to H-W predictions.
FIS > 0,
then there are fewer heterozygotes than would be expected if each deme was at H-W equilibrium.
FIS < 0
then there are more heterozygotes than are expected from an H-W population.
FIS < 0
then there are more heterozygotes than are expected from an H-W population.
Inbreeding refers
to the mating of organisms closely related by ancestry.
increases as a population decreases
Causes a decrease in heterozygosity
More highly related individuals are more likely to share the same allele at any given locus
Inbreeding depression
is a reduction in fitness in offspring due to inbreeding among parents
is not always the result of inbreeding
ex: rare, deleterious, recessive alleles (Tay-Sachs, sickle cell anemia, etc.)
inbreeding coefficient (f)
estimate average inbreeding by comparing the observed heterozygosity of a population (HO) with the expected
heterozygosity (HE) calculated from H-W
probability that two alleles at a randomly chosen locus are identical
by descent
F = 0.58
It is 58% likely that two alleles at a randomly chosen locus are identical by descent.
FIT
estimates divergence between the average heterozygosity of individuals in one or more demes as
compared to the theoretical value for the entire (merged) population)
- the combination of both FIS and FST
FST
estimates divergence between the expected average deme heterozygosity as compared to the theoretical value for the entire (merged) population)
Fst = 0
then each subpopulation has
the same allele frequencies. In this case, the predicted deme heterozygosities would all be the same as that of the merged population.
FST = 1
Variation between populations: 100% Variation within populations: 0%
FST = 0
Variation between populations: 0% Variation within populations: 100%
FST = 0.11
Variation between populations: 11% Variation within populations: 89%
Adaptation
When genetic factors cause differences among individuals in survival and reproductive success, evolutionary change comes about through natural selection.
-Individuals whose traits enable them to achieve higher rates of reproduction leave more descendants, and therefore the
alleles responsible for those traits increase in the gene pool of the population.
Natural Selection
the process whereby organisms better adapted to their environment tends to survive and produce more offspring.
1. There is variation among individuals in a population.
2. The variation is heritable.
3. Differences in survival and reproductive success, or fitness, related to that variation.
*
Survival and reproduction are not random but are related to variation among individuals. Organisms with the best characteristics are ‘naturally selected.’
Types of Selection
stabilizing
directional
disruptive
Stabilizing selection
works to “stabilize” traits by pushing a population toward an average or median trait.
Disruptive selection
increases phenotypic variation in a population
Directional selection
Directional selection is a mode of natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype
biotic community
refers to a dynamic assemblage of species in a specific area and time
-
its structure is the result of how these organisms interact with each other
Communities are commonly characterized by:
community structure and productivity
- Community structure
the species composition, especially as relates to their ecological niche
* relative abundance of species
* species growth characteristics
* types and magnitudes of species interactions (ex: food webs)
Symbiosis
refers to two or more species live intimately together with their fates linked
Coevolution
refers to the influence of closely associated groups on each other in their evolution
Can be inter- or intra- specific
Often influenced by predator-prey interactions
ecological niche
describes either the role played by a species in a biological community or the total set of environmental factors that determine a species’ distribution
R-Strategist Species
Emphasize high growth rates
Produce many offspring (ie. high r, low K)
High fecundity, small body size, early maturity, ability to disperse offspring, short generation time
Semelparous
Typically exploit less crowded niches
K-Strategist Species
typically living at high densities close to carrying capacity (K)
invest more heavily in fewer offspring, which have a high probability of surviving to adulthood
Large body size, long life expectancy, fewer offspring, extensive parental care Iteroparous
-
Typically strong competitors in densely populated niches
Logistic growth equations
model intra-specific competition
The Niche Concept
The coefficients can be used to estimate the effects of competition and niche overlap
* The greater the degree of competition/niche overlap (greater similarity), the larger the value of the competition coefficient.
* If two species really do occupy the same niche, the coefficients would be 1.0
* The addition of an individual of the competing species has the same effect of depressing the growth rate of the other species as does the addition of a conspecific
Gause’s axiom
No two species may occupy the same niche in the same environment. One will inevitably competitively exclude the other.
- When two species compete for the same resource, one will exclude the other from that resource
Character displacement
refers to an evolutionary change that occurs when natural selection favors the divergence in character (morphology, ecology, behavior, physiology, etc.) in two similar species that inhabit similar niches in the same environment
allopatric
and not competing, members of these two species have overlapping beak depth (and food habits) with G. fortis having slightly deeper beaks on average.
sympatry
selection acts to favor divergence of beak depth.
Niche partitioning
refers to the process by which natural selection drives competing species into different patterns of resource use or different niches
Foundation Species:
species that have a strong role in structuring a community
usually a primary, often one the produces the greatest percentage of cover in a given habitat/ dominates in terms of biomass.
example: coral, kelp, trees
Keystone species
species with a disproportionate effect on community/system function; often low in numbers and biomass but large in effects.
Most commonly apex predators
Ecological Engineers
effects can be very large if engineer species reach high densities
Results of Biotic Interactions- Short-term responses
result either in the local extinction or displacement from a particular resource of one species by another (competitive exclusion and niche partition).
Results of Biotic Interactions- Longer-term evolutionary
responses of populations to competitive and other types of interactions allow or even encourage populations to co-exist in the same area.
Characterization of Community Structure
The abundance of individuals at different trophic levels
Biomass of each trophic level
Fixed energy found at a given trophic level
Trophic levels
refer to role-defined groupings where energy/material source and flow are the defining characteristics
- not defined primarily by taxonomy, but by their ecosystem function
Complexity
refers to the number of trophic levels and the number of species at each trophic level in a community
-
Diversity = complexity
-
The diverse community may not be complex if all species are clustered in a few trophic levels
Connectivity
refers to a set of interconnected food chains within an ecosystem
The highly interconnected community may have many trophic levels, some of which can be compartmentalized
Species complementarity
occurs when species exhibit various forms of niche partitioning that allow them to capture resources in ways that are complementary in space or time
- interspecific interactions enhance the capture of resources by species when they are together
Community Diversity
the populations of different species that naturally occur and interact with a particular environments
Ecosystem Diversity
the variety of different habitats, communities, and ecological processes
Energy
is a central requirement of living things
Energy pyramids depict the fixation (storage) of energy at different tropic layers and therefore energy’s movement from one layer to another.
First Law of Thermodynamics
energy can not be created or destroyed; it can only be transferred
Second Law of Thermodynamics
with each successive energy transfer, less usable energy is available to perform work.
Entropy (disorder) increases.
Due to the Second Law of Thermodynamics,
energy is lost at each level of the pyramid.
* Energy is lost as heat in metabolic processes.
* 10% Rule (Energy / Biomass transfer)
* when energy is passed in an ecosystem from one trophic level to the next, only ten percent of the energy will be passed on
ecological Efficiency
refers to the efficiency with which energy is transferred from one trophic level to the next
abundance
of organisms in a given trophic level is proportional to the amount of energy transfer available
Bottom up- Mechanisms for Community Stability
primary production controls community complexity – the more energy, given enough time, the more complexity.
Top-down- Mechanisms for Community Stability
consumers (broadly considered – herbivores and predators) control the community
Complex interactions- Mechanisms for Community Stability
determined by many factors, including disturbances, mutualistic interactions, etc.
Trophic cascades
refer to significant effects on community structure that occur when certain key species change in abundance or habit
effects on these species propagate (cascade) through multiple trophic levels
typically the effects alternate in magnitude in every other trophic level
Habitat fragmentation
occurs when parts of a larger and contiguous habitat are destroyed, dividing into smaller, isolated areas (“patches”)
Habitat Island
distinct patches of habitat surrounded by less contrasting matrix types.
Species richness generally increases with patch size
Larger plots more likely to have more habitat and more niches
Habitat heterogeneity
refers to small-scale changes in resource composition and structural complexity
Patch
: an area of distinct habitat types isolated from other such areas
an area that differs from its surroundings
an area that can support a breeding population of some focal species “Patchiness” = density of different patches in some area
Extent
the area of a patch or something under study
Grain
the scale over which differences relevant to some species occur within a patch
the smallest resolvable unit of study (landscape ecology)
Usually relative to a given species and the scale over which it responds to
differences
“Grain” or “Grainy” = resolution
“fine grain” = fine resolution
Natural
Geological processes
Ecosystem engineers
—Beaver dams Environmental disturbances
Volcanism, fire, [non-human-induced] climate change
Carboniferous rainforest collapse
Anthropogenic
Land clearing
Deforestation
Agriculture
Rural development
Urbanization
Hydroelectric power
Exogenous
Independent of species biology
Habitat degradation, subdivision, isolation
Lead to a decrease in the density of species, increased competition, increased predation, etc.
Often result in dispersal, movement, or changes in seasonal migration
Endogenous
Develops as part of species biology
Behavior, interactions between species, and reproduction
Result in changes to breeding patterns or migration patterns
Often triggered by exogenous processes
Detrimental fragmentation
depends on the characteristics of the organisms found there. Many systems evolve to include a certain amount of fragmentation
Reduction in size of habitat patches
Increase in spatial isolation
Fragmentation Process- two distinct processes
gap formation and direct fragmentation
Gap Formation
Gaps can be benign or lead to fragmentation
Roads are significant drivers of habitat fragmentation
Increased mortality & injury
-Collisions, roadkill
- Diversity of scavengers killed feeding on roadkill
Altered habitat
-Greater edge effects, harsher boundaries
Noise pollution
-Interferes with vocal communications: organisms compensate by increasing the amplitude or pitch of their calls
Artificial light
-Impacts some species’ ability to migrate
-Attracts invertebrates (via phototaxis), which attracts predators (increased vulnerability to collisions)
Reduced migration
-increasingly isolated populations
Roads lead to a reduction in genetic diversity
Long-term impact on fitness not yet understood
-
Barrier effects: reduced gene flow due to road avoidance behavior or road mortality
-
Depletion effects: road mortality causes reduced population abundance
-
Genetic drift is enhanced in small, fragmented populations
Edge effects
refer to changes in population or community structures that occur at the boundary of two or more habitats
Transitions from edge to core are a complicated topic.
Natural systems have such transitions and species that inhabit them
* Species in transition areas are not all uniformly affected by the differences there as compared to core areas
* Some species mainly live in transition areas
* Disturbance magnitude varies (narrow roads are not the same as
super highways)
* More true core habitat is lost than appears and area-sensitive
species are especially affected
Species richness
is related to the size of a patch
Species-area curve
Reduction of patch size results in higher extinction rates
Faunal relaxation
the number of species declines following habitat fragmentation (reduced patch area and increased isolation)
Theory of Island Biogeography
predicts that the species richness observed on an island is the result of the interplay between three fundamental processes
Species richness = equilibrium
extinction
colonization (the dispersal and establishment of
species from the continental landmass to an island)
immigration
speciation (the generation of new species)
Area-sensitive species
require a certain size of habitat in order to thrive
Some species are found in all fragments (A & B): less area-sensitive at this scale
Some species only occur on larger fragments (C & D): more area-sensitive at this scale
Ultimately, all species are area-sensitive at some scale
Fragmented Critical Landscape
organisms requiring one specific type of landscape
Habitat fragmentation with
a species that requires several habitat types
Species Most Vulnerable to Fragmentation Loss
Wide-ranging (area-sensitive and area-dependent) Poor dispersers
Specialists
“Patch interior” species
Low recruitment species Exploited or persecuted species
Hylocichla mustelina
Stream Fragmentation
Impacts include:
Population fragmentation Altered habitat
temperature, depth, flow rates, etc. Silting/Desilting
Edge Effects & Reserve Management
Traditional reserve management stopped at the reserve boundary.
Today: more recognition that water, nutrients, and organisms move across boundaries
-Neighboring land use is critical
-Minimize contrast between path and “matrix” (buffer zones)
-Minimize the amount of edge
-Consider connectedness (corridors and stepping stones)
Corridors
refer to areas of habitat connecting wildlife populations separated by human activities or human structures
what does a corridor do for a habitat
Allow exchange of individuals
Increase colonization: species able to move and occupy new areas when resources are lacking in their native habitat
Increase migration: species capable of seasonal relocation
Increase interbreeding: find new mates in neighboring regions
how are corridors categorized
-Regional: greater than 500m wide
–Connect major ecological gradients (ex: migration
pathways)
-Sub-regional: 300-500m wide
–Connect larger landscapes features (ex: ridge
lines and valley floors)
Local: connect remnant patches
Stream Fragmentation impacts
–Population fragmentation
–Altered habitat
-temperature, depth, flow rates, etc.
–Silting/Desilting
Potential Problems with Corridors
Facilitate movement of non-target species such as:
–Non-native species (species not from the habitat)
–Pathogens (disease)
-Facilitate movement of disturbances (fire)
-Potential outbreeding depression (if gene flow disrupts local adaptation)
the ecological trap of corridors
Organisms try to live in the corridor and suffer edge effects
Higher mortality when moving through the corridor (more human contact)
edge effects
are changes in population or community structures that occur at the boundary of two or more habitats. Areas with small habitat fragments exhibit especially pronounced edge effects that may extend throughout the range.
Metapopulation
refers to a spatially structured population that persists over time as a set of local populations in balance between local extinction and colonization.
colonization and extinction of patches
Turnover of occupied sites
*
Empty sites are critical for persistence of the metapopulation
If extinctions are asynchronous and there is sufficient movement between patches, then the whole metapopulation can persist
Patches go extinct, but new patches can be colonized
Levins Metapopulation Model
describes temporal changes in the regional abundance of a species by extinction and colonization of subpopulations of Extinction
Metapopulation can only persist if the rate of colonization (c) is greater than the probability of extinction (pe)
Extinction can happen if movement between patches becomes insufficient
the lower the rate of colonization, the more space for colonization is necessary
population extinct
-Reduced dispersal success could lead to metapopulation extinction
-A metapopulation may be doomed to extinction long before all habitat is gone
-Arrangement and connectivity of patches is just as important as the amount of habitat left
Summary: Problems with Fragmentation
Reduction in connectivity.
▪ Insularization (to make into an island) and isolation
* Simplification (loss of heterogeneity) of patches.
* Increased contrast between patches.
Specific mortality threats introduced by the modified landscape matrix.
▪ Initial exclusion – loss of rare species in converted areas
▪ Crowding - usually leads to population collapse
▪ Area-sensitive species
▪ Edge effects (including increased susceptibility to invasive
species)
▪ Small population effects
SLOSS Debate
was a debate in ecology and conservation biology during the 1970’s and 1980’s as to whether a single large or several small (SLOSS) reserves were a superior means of conserving biodiversity in a fragmented habitat. Since its inception, multiple alternate theories have been proposed. There have been applications of the concept outside of the original context of habitat conservation.
