Exam 3 Flashcards
Biological Populations are
a group of potentially interacting and breeding individuals (but can pretty much be anything we define it to be)
Study Population
Population we are studying (e.g. university undergrads taking a psych course)
What characteristics might we wanna know about a population?
- Size
- Trend (see if policies are actually working)
- Distribution
- Age structure
- interactions with other species (population ecology)
- carrying capacity
Trends can differ based on how we define a population… (give example)
A bird population in the Netherlands vs the whole of Europe vs Washington State has different trends for the same bird…
Wolf hunting population example
- Pop estimated at 1,123 before hunt
2. 20% of population killed in 3 days after the hunt by the hunters
Counting pop size
When populations are small or confined in some way, counting is possible
(ie migration or congregation)
But this is not as reliable as we might expect (recall waterfowl counting survey)
Population size when organisms are more spread out
Marking individuals and recounting (some species already have uniqueness between individuals (whale tales and tiger stripes)
*there are a lot of assumptions for this simple model
Assumptions for capturing and marking and recapturing populations
- “Closed” population: no immigration, emigration, births, or deaths in time between first and last capture
- Equal chance of capturing all individuals: BUT 1. could be more likely to trap young individuals (naive, etc) 2. Not always true in small mammal populations: they learn to like being captured (“trap happy” also “can only ever trap a crow once”, they learn, become “trap shy”
- Enough time between capture occasions for populations to mix
What if we cannot trap enough or meet the assumptions of the trap and recount model?
(Ex: coyotes)
We can use grids/quadrants: divide landscape into manageable units and randomly sample a subset
- can use these to determine density, distribution, and frequency of occurrence
*if there’s a lot of habitat variability, random sample is not as accurate
Transects can be randomly placed, uniformly placed, or some combination
- can use the data to extrapolate plant or animal abundance
- can also use evidence of animals: tracks, scat
Wisconsin example of pack sampling
Wisconsin surveyed for packs
- determined how many packs these surveys usually missed
- multiplied number of packs by average pack size
So how did calculate wolf population size in a state?
Animals are too dispersed and in too large an area to count directly: we can use transects (is the area occupied or not?)
Relative abundance
(Not directly tied to actual number)
- often used to examine differences between habitats, treatments, etc
Ex: when talking about disease, might just want to reduce pop… can look at relative abundance: areas culled vs not culled
Population change over time: measuring trends
Measuring as 4 primary components - immigration - emigration - births - deaths (Typically we focus on births and deaths (easier to measure))
Exponential population growth
- Discrete AKA geometric growth
- individuals added in pulses
- eg most bird species breed once a year - Continuous
- individuals added to population without interruption
- can breed all year
- e.g humans
Discrete population growth formula
If lambda > 1, then population increases
If lambda < 1, then population decreases
If lambda = 1 then population stays the same
(Lambda cannot be less than or equal to 0)
For discrete populations, we can calculate population size into the future by modifying the previous equation
Results in an ever increasing or ever decreasing population (ignores some rules of biology)
Note that there is no change in growth over time
- population does not run out of resources
Exponential growth - continuous growth
Demographic Rates
We can use demographic rates calculated across individuals to model population changes over time
- survival rates or age distribution
- fecundity
- cannot predict an individual outcome, but can predict groups
Life Tables
life tables are a summary of how survival and reproductive rates vary with age
- can use them to see how populations will change over time
- can use them to help us calculate:
- population growth (lambda)
- generation times
- examine how population growth changes as we change population metrics (adult survival, reproduction, etc)
Age Structure
can play a big role in how a population will change over time:
- is often defined by either ages (years, months, etc) or stage (pre-reproductive, reproductive, post-reproductive)
- is important because it tells us about potential of population in the future
Rachel Carson
silent spring author
- documented decline of juvenile birds - young birds not being produced
- documented bad effects of pesticides on the natural environment
- eagles eat fish from ponds that have DDT… this gets rid of calcium, making eggs super thin… the eggs then get squashed resulting in few juveniles
… in the 1970s, DDT was banned
Populations grow in proportion to
their size - leads to exponential growth
Populations cant increase indefinitely because
- reduced access to food
- increased competition
- disease rates can increase
- predation may increase
“r” tells us
about the rate of population increase or decrease
r = instantaneous births - instantaneous deaths
Carrying capacity
Logistic growth: population increases rapidly, then stabilizes at the carrying capacity, K, maximum pop size that can be supported by the environment
Density-dependent effects - negative population effects
- High densities can cause changes in behavior, physiology, development, and specific population parameters (e.g., reproduction and survival)
- examples: disease, parasites, competition (intra - females not getting enough resources), predators - more individuals leads to non-reproducing animals increasing
- likelihood of juveniles to survive depends on how many already in pop
Maximum growth of population is at
K/2
Harvest
the number of individuals removed from populations
H* is maximum sustainable yield
Positive effects of density dependence
- can swamp ability of predators to respond
eg. .. masting in trees (producing more acorns than squirrels can eat), schooling in fish, creche canada geese
Low densities can also negatively affect population growth:
- ability to find a mate is affected
- at low pop. densities, pop. growth is hurt: have to work harder to find a mate (Allee) effect)
What limits population growth and sets carrying capacity?
Abiotic and biotic factors
Abiotic factors
- not biology
- many factors can limit distribution:
- moisture, light, oxygen (especially in aquatic system), pH
recall tolerable temp range for goldfish (most organisms have a preference for temp)
Thermoneutral Zone
where an organism can spend most of its time without using energy
… climate change…
- what will happen to species ranges? species will have to move to adapt
- organism are moving north or higher in elevation to escape the heat
- most of land viable for wheat production in north america in 2050 will be in Canada and some in Alaska
Biotic environment
- invasive species example
- Opuntia cactus introduced from southern US to Australia in 1839
- an insect that grows on cactus produces red dye: so british brought it to Australia
- spread everywhere (destroyed desert)
- so introduced a moth that can kill cacti (prickly pear moth) - Interactions example
- Hawai’i
- Lava fields have few nutrients, especially NO2 (super limiting, especially in places that are mostly rock)
- invasive firetree fixes NO2 (dump it into soil… allows plants that couldn’t previously survive to do so, crowds out native species)
- changes spoils by increasing limiting
Interspecies interactions
Mutualism: good for both (lichens, ants/acacia)
Commensalism: good for 1 (epiphyte on a tree, mites on eyebrows/eyelashes)
Predation: good for 1, bad for other (predator/prey, host/parasite)
Amensalism: bad for 1 (allelopathy (black walnuts poisoning other plants)
Competition: bad for both
Competition
2 species often compete for resources; level of overlap will determine the strength of competition
Interference competition
directly competing
- by physically defending resources
- favors larger, stronger species/individuals
Exploitation competition
indirectly competing
- consuming resources more quickly/efficiently
- favors those that can consume resources quickly (ex hungry hippos game)
Niche Partitioning
way to reduce competition
- resource partitioning
- eg. warblers split of sections of the tree
- “stay in your lane” competition
Fundamental Niche
the habitat you can use in the absence of competition
Realized niche
the habitat you can use given the competitors around you
Results of competition can be
- either competitive exclusion (barnacles on rock) or competitive coexistence (hawk and owl)
- we can predict the outcome of competition if we know carrying capacity (k) and the nature of the competition between the species
- stable coexistence: both species persist
- unstable coexistence: one species wins, but which depends on initial conditions
- competitive exclusion: one species always
Mussel/barnacle Niche example
- Two species of mussel: Chthamalus tends to stay in upper intertidal zone, Semibalanus tends in lower intertidal
- but without competition, Chthamalus can survive in the lower intertidal
competitive exclusion
Isocline line
maxed out production based on species carrying capacity
When one isocline is completely above the other, we always have ____
competitive exclusion
When K1 and K2 meet their axes farther out than N1 or N2, there is
unstable coexistence
If alpha/beta are <1 then
species have little effect on each other; they dont have heavy direct competition
so when neither species has big impacts on the other, coexistence can ocur
If competition is very asymmtrical,
we will see competitive exclusion
if one species is able to garner the resources much better
If competition is relatively symmetrical and strong, then
(both good competitors competing for a lot of the same resources)
then competition will lead to competitive exclusion, but the winner is determined by initial conditions
If competition is weak and relatively symmetrical
(use only some of the same resources)
we should have coexistence
Complete competitors cannot coexist
True. If 2 organisms have completely overlapping niches, one will lose
Competition: cancer application
Cancer cell types can vary in their requirements (energy and oxygen needs)
- cells with high needs tend to be poor competitors
- therefore therapy cannot completely eliminate the competition of the cells that require a lot of energy - otherwise they will grow
- so treat patient to knock down tumour, but not get rid of it
Metapopulations
- cluster of smaller pops, each of which may have its own internal dynamics
- each patch can have its own growth rate, determined by birth and mortality rates
- some pops might produce more individuals than they can sustain
- emigration from those creates sources - some populations might have higher mortality than birth rates
- immigration rescues these populations and they act as sinks
- when individuals are attracted to sink habitat, we call it an ecological trap
Character Displacement
- sometimes one species cant run away
- Over evolutionary time, evolution can change characteristics of individuals to reduce competition and increase fitness
- character displacement can lead to displacement - in sympatric (live together) species, character traits are more diverged than when the species exist allopatrically (live apart)
How do we measure diversity? (community metrics)
- Abundance - count or index of organisms in an area
- richness - count of the number of species in an area (total number of species found in sample - recall trail cameras)
- evenness - relative proportion of species in an area
- diversity - accounts for both species richness and evenness
Problem with rare species
simple counts of species diversity can be misleading
- low abundance (i.e. rare) species can cause diversity metrics to change wildly
can get around this with diversity/evenness indices
Species diversity
Species diversity is a weighted measure that incorporates the number of species and their relative abundance
Shannons’s diversity index
- provides an index of uncertainty
- the more heterogeneous a group of organisms is, the more unvertainty we will have knowing the species of a random individual in our population
- the more species we have, the more uncertainty - so higher H values
Species Evenness = H/ln(s)
a description of abundances of species
- ranges from 0-1
- 0 means an uneven distribution
- 1 means species are evenly distributed
Biogeography
The study of patterns of species composition and diversity across geographic locations… How are organisms distributed?
Tropics are generally far more diverse than other parts of the earth
yes
How we can use islands as systems to understand communities
we need to know immigrations rates and extinction rates to know how many species are on an island
-
Island population communities
For new species to arrive at an island, they need to come from mainland or neighboring islands
- as we get more species on the islands, the niches become filled, so immigration becomes more difficult
- as more species accumulate, the probability one will go extinct increases (competition)
- a stable species number is where immigration rate = extinction rate
- as one species goes extinct, another comes in to fill its niche
- size and distance from island affect immigration and emigration rates
Distance: island communities
Near islands are more likely to be found by species on the mainland
- a near island should have greater species diversity than the far island
Area: island communities
With more area, more species should be present
-if large areas have more species than smaller areas: large islands should have lower extinction rates compared to small islands
Simberloff study
Reduced island sizes of mangrove tree islands
- resulted in fewer species on the islands
Arthropod diversity on Florida Mangrove Islands
what if everything was killed on a mangrove island?
- he termite-tented the mangrove islands
- surveyed before and then after every few weeks
- over the course of 2-3 yrs, the islands to returned to abt same diversity, but species composition was much different
Deforestation
similar to island model ideas
- began in the 1960s
- 15% of the rainforest has been lost globally ~half of rainforest biome altered
Fishbone pattern
- in rainforests when roads are put through, people start logging/farming off the roads and create islands of forest surrounded by people and farm deforested land
- study studying species-area relationships/fragmentation found that smaller area fragments of rainforest lost much of species diversity (even the 100ha fragments lost 50% of species in 15 years)
Single large nature reserve or several smaller reserves?
Single large may have more species diversity, but how close is it to mainland?
- could smaller islands be used as stepping stones
- debate is silly practically, because this situation rarely/never comes up
Disturbances
- Weak, frequent disturbances
e. g. wind damage to an old tree - now more light can fall in this area - severe, rare disturbances
e. g. hurricanes
Succession
- After disturbance, the ecological community often goes through a number of change
- Early species tend to be those that can grow quickly and disperse far (weedy species)
- Later species tend to be tolerant of competition (asymmetrical and strong competition occurs)
Glacier receding… primary succession
- after glacier retreats, rocky area opens up (pioneer stage - pioneer species take place)
- Dryas stage
- Alder stage
- Tree stage (spruce stage) - good at dealing w low nutrient conditions
Succession - climax community
- Species go through a number of stages which can last a year or decades
- eventually reach a climax community (tends to be stable over time)
- is beech and sugar maple trees here
