Quiz 2 Flashcards
what is predation
Species interactions in which one species obtains chemical energy through the consumption of another.
how do predators influence their environment
Changes in predator abundance can also significantly alter community structure and function.
In many systems populations exhibit cyclic behaviour, in which the abundance of predators and prey track each other.
Predators reduce prey numbers directly by eating them.
They also impact prey numbers indirectly by increasing stress which slows reproduction. The stress effect persists into the next generation.
How can introduced predators be bad
The Nile Perch (Lates niloticus) was introduced to Lake Victoria in 1954 to replace dwindling native commercial stocks caused by over fishing.
It has been implicated (both by predation and competition in the extinction of over 200 native fish species endemic to Lake Victoria.
Additional factors at work here include increased erosion and runoff and nutrient levels, and invasions by algae and water hyacinth (Eichhornia crassipes), which depleted oxygen in the lake.
what is herbivory
Species interactions in which one species obtains chemical energy through the consumption of another species.
Herbivory differs from predation because grazed plants typically don’t die.
Moderate levels of herbivory occur in all plant communities.
what is non-interactive grazing
Non-interactive grazing. In other cases herbivores do not control vegetation productivity. E.g. European Finches
what is interactive grazing
Interactive grazing. In many plant-herbivore systems the abundance of vegetation impacts herbivores, who have reciprocal impacts on vegetation productivity. eg. Snowshoe hares, tent caterpillars.
how can plants defend against herbivores
Plants have diverse adaptations to slow or prevent herbivory.
Physical (thorns, spines, phytoliths (microscopic bits of silica)) and chemical deterrents (secondary metabolites including: toxins, compounds that decrease palatability digestibility, and allomones (to attract predators of herbivores).
what is the red queen hypothesis
The Red Queen Hypothesis
Strong competitive interactions require continual adaptation (evolutionary arms race that species are required to participate in to persist).
how can herbivory affect an ecosystem
In some situations increases in the abundance of herbivores can fundamentally alter vegetation and community structure.
Shifting agricultural practices in their southern range have increased snow goose abundance.
Growing populations of lesser snow geese (Anser caerulescens caerulescens) have transformed Arctic wetland complexes by overgrazing.
how do number of species and patch area relate to each other
The number of species in a patch increases with increasing area.
General principle that applies in most ecosystems.
Large habitat patches / islands have more species than comparable small ones.
what is Darlington’s rule, and a general species area relationship
Darlington’s rule: a tenfold increases in island area results in the doubling of the number of species.
Species area relationships follow a non-linear power function (hyperbolic curve)
Expressed mathematically as:
Number of species (S) = c * area^z
where c and z are fitted constants
how many abundant and rare species are in an ecosystem
Communities typically have a small number of abundant species, some common species and many rare species.
Rare-moderately abundant species are the most frequent.
Typically, only a few species are dominant.
what are dominance diversity curves
Dominance-diversity curves plot the logarithm of abundance (y-axis) against their rank abundance (x-axis).
Diversity, evenness, and the importance of rarity can be visualized using dominance-diversity curves.
Steeper curves had lower species evenness.
what is evenness
Evenness: Similarity in relative abundance of species in a community
There are many diversity indices that incorporate measures of abundance / evenness (Simpson’s, Shannon-Weiner)
what is simpson’s index of diversity
Simpson’s Index of Diversity = 1 - D
where $D=∑_1^s(p_i)^2$
where pi = proportional abundance (ni/N)
ni = abundance of individual species
N = abundance of all species
Diverse = higher values; less diverse = lower values. Also provides a measure of the probability that repeated sampling will yield a different species.
what is the neutral theory of biodiversity
Patterns of biodiversity/abundance can be explained by random extinction and dispersal processes.
All species are functionally equivalent.
New species arise through random speciation events.
Species replacements are random.
Species replacements originate from the local communities and a larger meta-community.
Models based on these assumptions have a good fit with empirical rank abundance curves.
what is the theory of island biogeography
Theory of Island Biogeography: MacArthur and Wilson (1967)
Number of species on an island is a function of island size and isolation (distance from the mainland).
Larger islands have lower extinction rates.
Less isolated islands have higher immigration rates.
Island size and isolation affect the equilibrium between immigration and recurrent extinction of species.
This model is also neutral to species identity hut has an enormous impact on conservation biology.
what are niche dynamics
Characteristics of species (tolerances) are important and species interactions (especially competition) lead to niche partitioning.
The way that niche space is divided is variable, but partitioning typically results in:
- a few generalists that can tolerate a wide range of conditions and use a diversity of resources
- many specialists that have narrow tolerances and use more specific resources.
Patterns of relative abundance are sustained by feedbacks between abundance and extinction and colonization probabilities.
Generalists tend to be locally abundant and regionally widespread.
Specialists tend to have low abundance, and be locally rare.
what are three theoretical perspectives on abundance diversity patterns
We will cover 3 theoretical perspectives, but there are many more.
- Neutral Dynamics
- Niche Dynamics
- Multiple FIlter Model
what is the filter model of community assemblage
Patterns of diversity and relative abundance in communities are determined by multiple processes.
These processes can be conceptualized as a series of successive filters that act on the regional species pool to determine the composition of a community.
Dispersal limitation prevents some species from arriving.
Environmental filtering prevents some species from establishing and surviving.
Species interactions influence realized niches.
Fine-scale variation in environmental conditions is also important. How patchy an area is can affect some species. Microclimates, small scale variations, etc.
why do theories of abundance diversity patterns matter
- Predicting success of Species re-introduction
- Danger of invasive species
- Help predict how changes will affect how communities exist in the future.
- Tell us about empty niches
- Are some communities more or less vulnerable to change?
- Are some communities more or less vulnerable to invasion?
- Can we predict species that will be problematic invasives?
- What happens to community composition in a highly disturbed world?
what are invasive species
Invasive species are species that establish a new range where they persist, proliferate, and spread to the detriment of the environment.
what are exotic species
Exotic species. Species outside of its normal range that doesn’t cause damage.
what are the negative impacts of invasive species
The negative impacts of invasive species include depressed populations, local extinctions, and ecosystem restructuring.
Key mechanisms here are predation and competition.
After habitat loss, invasive species are recognized as the greatest threat to global biodiversity.
why are invasive species happening
The increased global movement of people and goods has caused an unprecedented rate of species translocations.
The number of exotic and invasive species is increasing.
Species invasions are human-mediated (intentionally and unintentionally).
Climate change is becoming increasingly important here.
what are the stages of invasive species
Invasion is a process that involves multiple transitions.
Transport, introduction, Establishment, Spread, Impact.
There are multiple barriers to invasion.
Most species that are transported do not become invasive.
Williamson estimates that approximately 10% of species successfully move from one stage to another.
(0.10.10.1*0.1 = 0.0001) = 0.01% chance of an individual species becoming invasive.
what’s the brown tree snake like
This species is native to Australia, Indonesia, Papua New Guinea, and the Solomon Islands.
It was introduced to Guam via military operations during / following WW2.
There are few natural predators and ample prey on Guam, and by 1970 it had colonized the entire island.
Population growth and predation caused the extinction of most of Guam’s native forest birds and bats.
what are the attributes of successful invaders
Considerable effort has focussed on Identifying traits of invasive species. Making good predictions is central to managing risk.
Generalization is challenging. Traits linked to invasion potential vary by environment and functional group.
Factors (historical)
- The number of propagules
- Residence time in new habitat
- Previous history of invasion
Factors (biological)
- Fecundity
- Short generation time
- Rate of population expansion
what makes a community vulnerable to invasion
Extreme environments (like the arctic) may be less vulnerable, but climate change is likely to alter this pattern.
Islands are extremely vulnerable. Lower diversity = more empty niches, recipient community is naïve (less adapted to competition, predation, etc).
Where human activities have shifted disturbances regimes outside of the range of natural variability invasive species yield persistent novel ecosystems.
More diverse communities are more resistant to invasion (the evidence is mixed here).
what are novel ecosystems
Novel ecosystems: ecosystems with species composition that has no precedent in that biome. Also called emerging or no-analog ecosystems.
Factors contributing include: unprecedented rates of species movement, loss of original species pool, significant changes in the abiotic environment.
what is bottom up resource control
The Abundance of Populations (and community structure) is limited by food availability.
Consistent with observations of biomass across trophic levels.
Widespread observational and experimental evidence shows that increasing nutrients increases productivity
what is top down resource control
Community structure and the abundance of populations is controlled by higher trophic levels (consumers, predators).
Higher trophic levels regulate system dynamics.
What’s an example of top down resource control
The intertidal zone on this coast is home to relatively simple invertebrate community.
Community includes 15-16 species
Experimental removal of starfish (Pisaster spp) changes a 15-16 species community to a 8 species community.
This is because the predation controls the population of mussels, without the sea starts, they grow in population, and outcompete other species like chitons. Other effects too.
How does predation have indirect and direct effects on other things in the ecosystem
Predation of herbivores limits competition and prevents the dominance of one species of mussel (Mytilus californicus).
Changes in starfish abundance impacts the abundance of things they eat (direct effects) and things they don’ eat (indirect effects).
what is a keystone species
A species that has an impact that is disproportionately large relative to its abundance in the ecosystem.
what are trophic cascades
A species that has an impact that is disproportionately large relative to its abundance in the ecosystem.
what are keystone resources
Keystone Resources: resources required by a large number of species. Ex. Course woody debris as habitat for cavity nesters, insects, fungi.
what are keystone modifiers
Keystone Modifiers: Species that create habitat by modifying ecosystems. Ex: Beavers and wetland creation.
what are cultural keystones
Cultural Keystones: Culturally salient species that shape the cultural identity of people. Ex: Cedar, Muskrats, Caribou.
how do the importance of top-down, bottom-up, and middle-out, controls relate and change
The importance of these effects varies in different systems, among species, and through time.
The emphasis has shifted to determining when and where different controls predominant?
The importance of different controls can also shift with environmental conditions.
In semiarid areas of Chile: wet years can shift the relative importance of top-down, vs bottom-up processes.
why is it important to know if an ecosystem is top down, or bottom up
- Focus of conservation efforts
- Effects of species lost
- Wolf culls, good or bad
what is trophic rewinding
Species introductions intended to restore top-down ecosystem control and initiate trophic cascades that promote biodiversity and ecosystem function.
what is standard deviation
If a set of data is normally distributed
68% of data is within 1 SD of the population mean
95% of data is within 2 SD of the population mean
The sample standard deviation is an estimate of the population standard deviation. More accurate with a larger sample size.
how does sampling effect statistics
We usually don’t know the population mean or the population Standard deviation.
We collect data to estimate these.
Size of a sample, randomness of data chosen, and lack of correlation between data points affect quality of sample representation.
Doesn’t always mean its necessary to get as many data points as possible, sometimes there is a limit of diminishing returns
what is standard error
We can obtain an estimate of the variation among sample means by calculating the standard error
Sx=S/√n
The standard error of the mean is estimated by dividing the sample standard deviation by the square root of the sample size.
The standard deviation of a sample statistic is called the standard error of the statistic.
what is the 95% confidence interval
(1.96) *the standard error of the mean is used to calculate the 95% confidence interval of the mean.
1.96 * SE = 95% CI
The 95% confidence interval is the range that 95 times out of 100 contains the population mean.
what is the general procedure for a statistical test
We perform statistical tests by comparing a test statistic with the probability distribution for that statistic
General Procedure.
- set up $H_0$ and $H_A$
- Determine test statistic
- Choose significance level (typically α = 0.05)
- Collect data
- Calculate and compare test statistic to a distribution
- reject or retain H0
There are many different tests. We will focus on tests that involve t-distribution (t-test)
what is the null hypothesis
Null Hypothesis H0
The hypothesis of no difference
Statistical hypothesis that is the opposite of our research hypothesis (ex: blueberry productivity is the same in 2009 and 2010)
what is the alternative hypothesis
Alternative hypothesis HA
Opposite of the null hypothesis (there is a difference0
Ex: blueberry productivity is different in 2009 and 2010
what is the t test formula
(x-u)/SE = T
x = population mean
u = theoretical mean
SE = standard error
tells use how unusual a given mean is compared to the expectations set out by the t-distribition
what does a t value give you
a p value which tells you the the probability of collecting these data given that the null hypothesis is true
what is type 1 error
Type 1 Error (α). Rejecting a null hypothesis when it is true. If we adopt alpha (α) of 0.05 as a significance threshold then differences we consider ‘significant’ would only occur by chance (when Ho is true) 5 times out of 100.
The “p-value” - The probability of collecting these data given that the null hypothesis is true.
what is type 2 error
Type 2 Error (β). Failing to reject a null hypothesis when it is false.
β = the probability of committing type II error (failing to reject Ho)
The probability of Type 2 error varies with sample size, the size of the difference we are trying to detect and variance.
what is statistical power
Statistical Power (1-β). Ability to detect the effect of a variable (probability of correctly detecting an effect)
what are the two characteristics of statistics
- Small samples provide less reliable estimates
- Standard error provides a way to characterize error in our estimates
what is a least squares regression
- Linear regression generates a straight line, ŷ = ax + b, that provides best prediction of y for any value of x
- The line is determined by minimizing the distance between the data and fitted line, i.g. the residuals
- The r squared (r^2) measures the match between the prediction line and the data (proportion of the variance in y that is explained by our regression line). It ranges from 0-1
what is succession
Succession is cumulative directional change in community composition in a given area through time
what is primary succession
Succession is cumulative directional change in community composition in a given area through time
what is a general pattern for vegetation change in temperate regions
Vegetation change: Mosses→Mountain avens (0-15yrs)→willows(15-35yrs)→Alder thickets(35-80 years)→Sitka spruce(115-200years)→Sitka spruce, alder, hemlock (>200 years)
This pattern is pretty similar across different areas.
does all succession follow the same pattern
In reality things aren’t so simple: Some areas can become stuck in an early stage, no making it to the final stages of succession.
what is Hydrach and Xerarch succession
Hydrach Succession: Pioneer community becomes established on a wet substrate. Succession at the edge of a shallow lake
Xerarch Succession: Pioneer community develops on a dry substrate. Ex: lichen and loss establishment on bare rock.
what is secondary succession
Succession on a previously vegetated site where the community is damaged or killed (there are a spectrum of impacts here).
Disturbances: forest fires, wind throw, logging, canopy gap creation, agricultural activity, etc.
Some seeds, spores, and vegetative propagules, and sometimes soil are present
Generally Things recover much more rapidly.
how do we study succession
Ideally we measure changes over time
Practically, we use space for time substitution
Ex: Find a site with a forest fire 5 years ago, another 10 years ago, another 50 years, etc.
Has problems, but saves decades of time.
what do thaw slumps tell us about succession in the arctic
One type of disruption in the low arctic is a thaw slump, where mud flows shift over time for years before stabilizing.
Secondary succession in thaw slumps don’t seem to approach the standard plant community composition. Though after 400-600 years, they get largely similar to standard tundra. So it takes a while.
Disturbances can be very heterogenous. In a forest fire, some spots are hotter than others, some get more burnt, etc. Which can have an impact on succession later on.
what is disturbance
Any “discrete event in space and time that disrupts ecosystem, community, or population structure and changes resource, substrate, or the physical environment” (Pickett and white 1985)
Disturbances have a range of impacts on ecosystems (spatially and temporally)
To a greater or lesser degree, disturbances reset the successional clock. Following most disturbances communities undergo succession, or directional change in community composition.
Disturbance maintains heterogeneity, diversity and function. Pivotal for normal functioning of ecosystems.
what are micro-disturbances
Micro-disturbances occur at fine scales (typically units of m^2)
Examples:
Tree death (gap formation)
Frost boils (Cryoturbation)
Animal burrows / grazing
The fine-scale patchiness created by micro-disturbance maintains compositional and functional diversity in ecosystems.
Micro-disturbances are surrounded by a large un-impacted areas, which strongly influence their recovery.
what are broad-scale disturbances
Disturbances that impact larger contiguous areas (typically units of km^2)
Examples:
Forest fire
severe pathogen outbreaks
Hurricanes
These disturbances impact entire landscapes / ecosystems.
AKA: stand-replacing disturbances
Fine-scale pattern within these disturbances and the surrounding ecosystem influence the nature of recovery.
Ex: unburned wetlands complexes within a fire.
what are disturbance regimes
At a given time and spatial scale a system can usually be characterized by the regimes of one or several disturbances.
Ex:
Boreal forest: 1) Stand replacing fires 2) Insects
Costal temperate Forest: 1) Canopy gap formation 2) insects/pathogens
Garry oaks stands: 1) Anthropogenic fires
High Arctic: 1) fine scale permafrost changes
High grass prairie: (In the past) 1) Fire 2) animal herds
how can you describe and individual disturbance
Individual disturbances can be described in terms of their:
Spatial extent (size of the area affected)
Intensity (crown vs surface fires)
Regularity (how often do they happen) return interval (time between events) frequency (# events / time)
Timing (spring flood, fall flood)
The disturbances that an ecosystem experiences, including their intensity and frequency, describe their “disturbance regime”
generally the frequency of disturbances is inversely proportional to its size and severity (ie. Infrequent disturbances are larger and more severe)
why do we care about succession
Tell us about health of the ecosystem.
Tell us if an area could recover after logging or other land usage.
how much can we generalize about the changes that occur as part of succession
How much can we generalize about the changes that occur as part of succession? We can get a pretty good sense from the environmental conditions, but it has a lot of variability.
Environmental conditions and the regional species pool set up the context for succession.
On Vancouver island a mild and wet climate leads to the development of productive coniferous forest (time scale here is 500+ years)
If our climate was colder and drier, succession would look different.
what was an early (but wrong) view of succession
Succession moves through a series of stages until reaching a stable climax community.
Changes are predictable and lead to a single ‘climax community’
In the absence of disturbance the climax community is capable of self perpetuation (recall Frederick Clements’ organism metaphor).
Equilibrium condition with no directional or cumulative change in species composition.
what is a modern view of succession
Trajectories are influenced by many factors and prediction can be challenging
- Distance to seed sources (Glacier Bay, Yellowstone NP)
- Timing of disturbance (field abandonment)
- Fine scale variability (moisture, nutrients, etc)
Succession doesn’t proceed to a single end point.
- Polyclimaxes - succession with multiple end points
- Disclimaxes - frequent disturbances limits succession
- Edaphic climax - local variation in soils limits succession
what are alternative stable states
Alternative stable states are different ecological configurations (structural and functional) that occur in the same place under similar environmental conditions
The stability of each state is maintained by positive strong feedback
Example: Longleaf pine / oak
young and mature pines can survive ground fires, but oaks cannot
Mature pine supply fuel for ground fire.
Oak leaf litter suppresses fire
Many ecosystems can persist for long intervals in one of several stable configurations
succession can lead to different configurations or systems can undergo rapid transitions
Shifts between states may occur because of changes in disturbance regimes, environmental conditions, population size, etc.
what are some examples of alternative stable states
Examples:
- Black spruce forest / heathlands
- Sedge wetland / hypersaline barrens
- Kelp forests / urchin barrens
- Oligotrophic / eutrophic lake
- Arid shrubland / desert
what is resilience and resistance
Ecological resilience (resistance in the textbook). The magnitude of disturbance that an ecosystem can absorb without exhibiting a fundamental shifts structure and function (Holling 1973)
What kind of fire (severity / return interval) will flip the system from oak to pine?
Recovery time (engineering resilience). the time it takes variable to return to equilibrium following a perturbation (Pimm 1984)
^ this is engineering resilience, used in textbook, but not right definition.
what are traits
One component of biodiversity is the diversity in species characteristic (or traits)
Traits are a variable measured on an organism
A functional trait is “a trait arising from or influencing an organism’s fecundity, growth, development, or survival”
what is functional diversity
“the extent of trait differences among a set of organisms
Can arise both from intra and interspecific trait variability
what is intraspecific trait variability
Variation in traits between individuals of the same species
Phenotypic plasticity or local genetic adaptation
With phenotypic plasticity, placing the offspring in a different environment would change their phenotyp, while with local genetic adaptation it would not
what is interspecific trait variability
Variations in average traits between species
traits usually vary more between species than within individuals of the same species
Important at the community level
what is functional diversity and composition
Functional diversity: the range of trait values in the community
Functional composition: the average trait in the community
what are response and effect traits
Response trait: a trait whose values determine how individuals respond to environmental conditions. Ex Bark thickness - fire tolerance
Effect trait: a trait which influences the properties of an ecosystem
Ex Leaf nitrogen content - nutrient cycling
Response traits affect how an organisms react to environmental change like ecosystem degradation or climate change
Then Effect traits affect how an organism effects the Ecosystem processes like Ecosystem functions orEcosystem services
what is an ecological filter
Can be abiotic (e.g. cold) or biotic (g.g predation)
Can act on intraspecific (e.g. height of yarrow) or interspecific (e.g. amphibians in ponds) trait variability
Only individuals and species with traits that allow them to pass the filter survive
- Reduces number of species
- Changes functional composition (i.e. average trait values)
- Reduces functional diversity(i.e. variation in trait values)
what is the dominant species effect
- Ecosystem functions are dependent on the trait values of the dominant species in the community (i.e., the functional composition)
what is the complementarity effect
- Ecosystem functions are dependent on the differences in trait values of species in the community (i.e., the functional diversity)
- Species with different traits have different ecological niches, which leads to reduced overlap and higher complementarity in resource use
- Reduced competition for resources enhances ecosystem functions that depend on those species
what is biological insurance
- Ecosystem functions are more stable in the face of disturbances when there are:
- Multiple species with same function (i.e. low functional diversity in effect traits)
- Variety of responses to disturbances among species that share the same function (i.e. high functional diversity in response traits)
what is dominance, complementarity, Biological insurance
Dominance: Functional composition as a driver of ecosystem functioning
Complementarity: Functional diversity as a driver of ecosystem functioning
Biological insurance: Redundancy in effect traits and diversity in response traits as a driver of ecosystem stability.
what is ecological restoration
“Process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed”
Which species or ecosystem functions to foster in the restored ecosystem?
How to re-establish those species and functions in the ecosystem?
how do response traits affect species performant and restoration success
- Meta-analysis of grassland restoration in Britain:
Grass were better overall
Other herbs with traits for high colonization ability (like relative growth rate) had better establishment
Other herbs with traits for high competitive ability (like height) had better persistence
how do effect traits impact ecosystem functions and services
Specific leaf area → Decomposition and soil fertility
Wood density → Carbon storage
Flower shape → Pollination
Dispersal type → Dispersal
how can we use knowledge of functional traits for restoration
Knowing what traits have a specific effect on an ecosystem can be more useful than knowing what species have a certain effect on an ecosystem, since a different ecosystem might have different species, but they still might have those desired traits
how do effect traits affect restoration
Delivery of functions and/or services
Use effect traits to design target communities that provide specific functions and/or services
Selecting species for restoration based on effect traits related to C cycling increased aboveground carbons storage in Hawaiian forests
how do response traits affect restoration
Resilient communities able to withstand future environmental change
Use response traits to select species that will more likely survive ecological filters of current and or future conditions
How do functional diversity and composition of grassland communities impact their response to extreme drought events?
