Midterm 3/Final objectives

Define evolution, fitness, and adaptation using the biological definitions  

• Evolution

  • Process where populations of organisms change over generations due to genetic variations and natural selection.

  • Natural selection occurs when individuals with certain traits produce more offspring than those without those traits

  • Selected traits increase in frequency in pop from gen to gen causing evolution

• Fitness

  • Refers to an organism’s ability too survive and reproduce in its environment

  • Individuals with higher fitness pass on more of their genes to the next generation which allows their offspring to survive better as well

• Adaptation

  • A trait that improves an organisms ability to survive and reproduce in a specific environment which results from natural selection

    For example: polar bears with thick fur and fat insulation have high fitness because they can survive harsh winters and reproduce.

  • Over time these traits become more common in the population demonstrating evolution through adaptation caused by natural selection

Explain what darwin meant by descent with modification  

• Means that all organisms share common ancestors but have changed over time through gradual modifications.

• These changes occur due to genetic variations, and the traits that provide an advantage in survival and reproduction are passed on to future generations through natural selection

• Over many gens this process leads to the genetic diversity of life we see today

• For example, Darwin observed that finches on the Galapagos islands had diff beak shapes depending on their diet

  • Their ancestor prolly had a general beak shape, but as populations adapted to different food sources their beaks evolved to become more specialized demonstrating descent with modification

Compare and contrast transitional features and vestigial traits 

Transitional features= traits in a fossil species that are intermediate b/w ancestral and derived species

Vestigial traits= reduced/incompletely developed structures that have no or reduced function

BOTH

• Evidence for evolution

• Connect ancestors to modern species

Differences

• Transitional features show active changes b/w evolutionary stages while vestigial traits are remnants of past traits that aren’t needed anymore

• Transitional fts help explain how new traits evolved wheras vestigial show what was once useful has now become obsolete

Examples

• Transitional: The fossil record of horses. Modern horses have just one toe (the hoof) but the ancestors had 4 toes

• Vestigial: Appendix (humans), wisdom teeth, pelvic bones of whales, reduced flight in flightless birds, goosebumps (humans)

Describe Darwins 4 postulates, why are they important 

1. Individuals in a population vary in their traits

   • ex: some beetles green others brown

2. Some of the differences are heritable

3. In each gen, more offspring are produced than can survive

   • ex: brown beetles blend into envt better than green so makes them less likely to be eaten

4. Individuals with certain heritable traits more likely to survive and reproduce than others

   • Natural selection occurs when individuals with certain traits produce more offspring than those without those traits

   • Individuals selected naturally by env’t and over gens brown beetles become more common while green beetles decrease

Important because: Explain how evolution by natural selection works and shows that species arent static and change in response to their env’t. They help scientists understand biodiversity, adapation, and even antibiotic resistance in bacteria.

Distinguish b/w aritifical selection and natural selection  

Natural Selection

• Driven by nature- environmental pressures determine which traits are beneficial

• Survival based: Organisms with advantageous traits survive and reproduce more successfully

• ex: In the wild faster gazelles more likely to escape predators so over gens the population becomes faster

• Gradual over many gens

Artificial Selection

• Driven by humans: Humans choose specific traits to breed for

• Traits selected based on human preference rather than survival advantage

• Ex: farmers breed cows that produce more milk or dogs with physical features like pugs snout

• Can be rapid

Explain why an individual organism cannot evolve  

Evolution is a long-term process that requires genetic variation, selection, and inheritance across multiple generations. While individuals can adapt physiologically or behaviorally within their lifetime, they cannot evolve because evolution is a change in the genetic makeup of a population, not an individual.

1. Genes don’t change in 1 lifetime: An Individual is born with a fixed set of genes that don’t change during its life. Evolution requires changes in frequency of genetic traits across gens

   • ex: giraffe cant grow a longer neck, only offspring that have slightly longer necks due to genetic variation may have an advantage and pass that trait on

2. Evolution requires population level changes

   • Evolution happens when certain traits become more common or rare in a pop due to differential survival and reproduction

   • ex: If only the fastest cheetahs survive and reproduce, futre gens may have more fast indivs but a single cheetah cant evolve to become faster in its own lifetime

3. Adaptation happens across generations

   • Individuals may adjust to their environment but these changes can’t be passed on

Identify common misconceptions about evolution and adaptation and give examples to illustrate why they aren't true  

• Individuals evolve

  • A single organisms can’t evolve during its lifetime

  • Evolution occurs over many generations in a population

  • Ex: A giraffe cannot stretch its neck to make it longer, but over many generations, giraffes with slightly longer necks (due to genetic variation) may have a survival advantage, leading to a gradual increase in neck length in the species.

• Evolution has a goal or purpose

  • Evolution does not work to create better or perfect organisms

  • it isnt goal oritented, its a response to changing environments and selective pressures. Organisms evolve traits that allow them to survive but they aren’t perfect necessrarily

  • Ex: Penguins have wings but they aren’t for flight, instead adapted for swimming. Evolution didnt plan this, those with better swimming ability survived and reproduced.

• Organisms adapt b/c they need to

  • Wrong b/c adaptations arise through random genetic mutations and those that provide a survival advantage are passed on through NS. Organisms cant will themselves to adapt

  • Ex: fish living in dry pond cant grow lungs b/c it needs to breathe air. Instead, if some fish randomly has genes that allow it to survive in low O2 it will reproduce more, over gens the pop may evolve

• Evolution always leads to more complex life forms

  • Wrong b/c evolution favors traits that improve survival whether they lead to simplicity or complexity. Sometimes losing fts is beneficial.

  • ex: cave dwelling fish lose their eyes b/c sight is useless in the dark, and it wastes energy maintaining eyes.

Describe why evolution is not perfect  

Not perfect b/c it works with existing genetic variations and favors traits that are “good enough” for survival and reproduction in a given env’t rather than perfect ones.

Also, evolution is limited by random genetic mutations, meaning that not all possible beneficial traits will arise.

Many traits also have trade-offs where improving one ft can come at the cost of another, such as investing energy in reproduction and investing in survival.

B/c environments are constantly changing, evolution can only select traits that are advantageous at the moment, not those than might be useful in the future. As a result, organisms are often adapted to their enviornments in ways that are effective but not perfect.

Also takes a long time because it occurs over generations. It can take a thousand or mill yrs. This means than when env’ts change rapidly such as due to climate change or human activity, evolution may not be able to keep up and produce the best adaptations.

Test whether evolution or nonrandom mating is occuring at a particular gene, using the Hardy-Weinberg principle 

1. Determine allele frequencies (P+q should =1)

   1. Identify 2 alleles of the gene (ex: A and a)

   2. Count # of indivds with each genotype: AA, Aa, aa

   3. Calc allele frequencies

   p= 2(AA indivs) +Aa indivs/2N

   q= 2(aa indivs) +Aa indivds/2N

   p= allele frequency of A, q=allele frequency of a, N= total # individuals

2. Calc expected genotype frequnecies (HWE)

   • If pop is in hardy weinberg equilibrium (no evolution or nonrandom mating) frequencies show be

   • AA= p²

   • Aa= 2pq

   • aa= q²

   • Multiply these frequencies by the total # of indivs N to get expected counts

3. Use chi square to compare observed and expected genotypes

4. Interpret results

   • p> 0.05 the pop is in hardy weinberg equilibirium, suggesting no signficiant evolution or nonrandom mating at this gene

   • p<or equal to 0.05 the pop isnt in equil indiciating evolutionary forces (NS, mutation, migration, geen drigt) or nonrandom mating may be affecting this gene

Describe the 4 evolutioanary mechanisms and list whether each one causes adaptation, introduces new alleles, acts randomly, or causes genetic variation to increase or decrease  

1. Natural selection

   • process by which indivs with advantageous traits survive and reproduce more successfuly, increasing the freq of beneficial alleles

   • Causes adaptation: YES

   • Introduce new alleles: NO

   • Acts randomly: NO (selection favors specific traits)

   • Gen variation DECREASES (b/c less favorable alleles removed)

2. Mutation

   • Random change in an organisms DNA which can introduce new alleles into a pop. Ultimate source of gen vsriation.

   • Causes adaptation: NO (mutations occurs randomly)

   • Introduces new alleles: YES

   • Acts randomly: YES

   • Gen variation INCRASES

3. Genetic drift

   • A random change in allele frequencies due to chance events, especially in small pops. This can lead to loss of alleles

   • Causes adaptation: NO (random, not based on fitness)

   • Introduces new alleles: NO

   • Acts randomly: YES

   • Gen variation DECREASES (alleles an be lost due to random chance)

4. Gene flow

   • Movement of alleles b/w pops due to migration, which can introduce new genetic material

   • Causes adaptation: NO

   • Introduces new alleles: YES (from other populations)

   • Acts randomly: NO (depends on movement patterns of organisms)

   • Gen variation INCRWASES (adds diversity by bringing in new alleles)

Evolutionary Mechanism	Causes Adaptation?	Introduces New Alleles?	Acts Randomly?	Genetic Variation (⬆ or ⬇)

Natural Selection

✅ Yes

❌ No

❌ No

🔻 Decreases

Mutation

❌ No

✅ Yes

✅ Yes

🔺 Increases

Genetic Drift

❌ No

❌ No

✅ Yes

🔻 Decreases

Gene Flow

❌ No

✅ Yes

❌ No

🔺 Increases

Compare and contrast the effects of directional selection, stabilizing selection, disruptive selection, and balancing selection  

Selection Type	Effect on Trait distribution	Gen variation	Ex
Directional	Shifts pop toward one extreme phenotype. If it continues favored alleles approach freq 1, disad approach 0.	🔻 Decreases (removes less favorable alleles)	Antibiotic resistance in bacteria (favoring more resistant strains)  Clif swallow birds, survivors were larger birds due to bigger fat stores.
Stabilizing	Favors the intermediate phenotype, reducing variation	🔻 Decreases (eliminates extreme traits)	Human birth weight (very small and very large babies have lower survival rates)
Disruptive	Favors both extreme phenotypes over the intermediate form  OPP effect of stabilizing	🔺 Increases (maintains multiple phenotypes)	Beak size in finches (large or small beaks are better suited for different food sources)
Balancing	Maintains multiple alleles in a population, no single allele has a distinct advantage	🔺 Maintains variation (allele frequencies stay balanced)	Sickle-cell trait in malaria-prone regions (heterozygotes have an advantage)

Explain why inbreeding and assortative mating may act to change genotype frequencies but don’t change allele frequencies 

• B/c affect how alleles are combines rather than introducing or removing them from population

• Interbreeding

  • Occurs when closely related indivuals mate, increasing homogzygosity and decreases hetero (fewer Aa) making recessive traits more common.

  • However, since no alleles added or lost, overall allele frequncy unchanged

• Assoritve mating similarily

  • Where indivs choose mates with similar traits increases homozygous indivs and reduces heterozygotes

  • ex: if indivs with blye eyes mate with other blue eyes than freq of blue eyed genotype may increase but the total porportion of allele responsible for blue eyes doesnt change

Define sexual seletion. Explain which sex is more strongly affected by sexual selection and why.  

Sexual selection is a form of natural selection in which individuals with certain traits have a greater chance of attracting mates and reproducing. These traits may not necessarily increase survival but enhance reproductive success.

Sexual selection occurs through two main mechanisms: intersexual selection (mate choice, where one sex selects mates based on desirable traits) and intrasexual selection (competition within the same sex for access to mates).

Typically, males are more strongly affected by sexual selection because they often compete for access to females, who are the limiting factor in reproduction. In most species, females invest more in offspring through larger gametes (eggs), pregnancy, or parental care, making them more selective when choosing mates. As a result, males develop elaborate traits—such as bright feathers, or courtship behaviors—to increase their chances of being chosen by females or against rivals. This difference in reproductive investment drives stronger sexual selection pressure on males, leading to greater variation in male reproductive success compared to females.

Explain the roles that gene flow selection, genetic drift, and mutation play in the process of speciation  

Gene flow

• Refers to movement of alleles b/w populations due to migration or interbreeding.

• High gene flow prevents speciation b/c it homogenizes genetic differences between populations, keeping them genetically similar

• Low/no gene flow allows populations to diverge independently, increasing the likelihood of speciation. This is important in allopatric speciation where geographic barriers prevent gene exchange

Genetic Drift

• =Random change in allele frequencies due to chance events, specifically in small populations. Can contribute to speciation by:

• Spreading unique alleles in isolated populations leading to genetic divergence and making them diff from the og pop

• Founder effects, where a a few individuals of a population establish a new population with different gene pool, accelerating speciation

• Bottlenecks, where pop size drastically reduces due to a disaster, only some traits survive, causing random genetic changes to the group

Mutation

• = random changes in DNA that are the ultimate source of genetic variation. Plays a role in speciation by

• Introducing new alleles that can make groups of organisms more different from each other, sometimes preventing them from interbreeding such as chromosomal mutations like polyploidy in plants that create new species

• It gives natural selection and genetic drift something to work with

Define, compare, and contrast the 4 species concepts 

• Biological species concept

• Morphological species concept

• Ecological species concept

• Phylogenetic species concept

Biological species concept

• A species is a group of organisms that can breed with each other and produce fertile offspring but not with other groups

• Strengths: useful for studying living, sexually reproducing organisms

• Weakness: Doesn’t apply to asexual organisms or fossils, and hard to test in species that don’t geographically overlap

Morphological species concept

• A species is defined by its physical traits (shape, size color etc)

• Strengths: Works for fossils, asexual species, and when reproductive data isn’t available. (widely applicable)

• Weakness: physical traits can vary within a species (ex: dog breeds) and some diff species look very similar (cryptic species). The features used to identify species under this concept are subjective. Only polymorphic species may be classified as more than 1 species.

Ecological species concept

• A species is a group of organisms that share the same ecological role/niche (ex what they eat or where they live)

• Strengths: useful for distinguishing species that look alike but behave differently

• Weakness: hard to define a niche completely, and a diff species can sometimes overlap in their roles

Phylogenetic species concept

• A species defined as the smallest monophyletic group on the tree of life

• Strengths: can be used for all organisms including asexual, and fossils. Logical b/c diff species have diff synapomorphies due to lack of gene flow and independent evolution

• Weakness: DNA data isn’t always avaibable, critics pt that it would lead to more species identification than either of the species concepts (more than what exists).

Describe 5 prezygotic isolating mechanisms and give an example of each 

• These are barriers that prevent diff species from mating or fertilizing an egg, stopping hybrid offspring from forming

1) Temporal Isolation (timing differences)

• Species breed at diff times (seasons, yrs, or times of day) so they don’t meet to mate

• ex: Weastern and western spotted skunks breed in diff seasons preventing interbreeding

2) Habitat Isolation

• Species live in diff habitats so they rarely/never meet

• Ex: land and water garter snakes live in diff envts so they don’t interact

3) Behavioral Isolation

• Species have unique courtship behaviors (songs, dances, calls) that others don’t recognize

• ex: fireflies flash diff light patterns to attract mates, preventing crossbreeding b/c species

4) Mechanical isolation

• Differences in reproductive organs make mating physically impossible

• ex: snail species with shells sprialing in opp directions can’t align to mate

5) Gametic isolation

• Even if mating occurs sperm and egg from diff species cant combine due to chemical differences

• exL sea urchins release eggs and sperm in water but only sperm from same species can fertilize the eggs

Describe the process of allopatric speciation and sympatric speciation and give examples of both  

Allopatric speciation (geographic isolation)

• Allopatric speciation occurs when a population is divided by a physical barrier (mountains, rivers, or oceans) preventing gene flow b/w populations. Over time genetic differences build up and this leads to formation of new species

  1. Geographic isolation (via dispersal (moving to new area) or vicariance (phys splitting of habitat) separates population

  2. Diff envts cause diff adaptations through natural selection

  3. genetic drift and mutations create more differences

  4. Reproductive isolation eventually prevents groups from mating even if they meet again

• ex: Darwins finches evolved into diff species after being sep on diff islands, adapting to diff food sources

Sympatric speciation (same location, no physical barrier)

• Happens when new species evolve within same area as o.g population, without geographic isolation. Usually due to external events like disruptive selection based on diff ecological niches or mate preferences. Or internal events like chromosomal mutations.

  1) disruptive selection, mutation like polyploidy, or behavioral changes cause individuals to diverge

  2) Reproductive barriers like diff mating times/food preferences keep groups from interbreeding

  3) over time, gen differences build up leading to sep species

• ex: apple maggot flies in NA originally laid eggs on hawthorn fruit but later some switched to apples. Over time, these 2 groups began evolving separately due to diff breeding times and food sources

Explain how polyploidy can lead to speciation  

Polyploidy is when an organism has extra sets of chromosomes due to errors in cell division.

• It can lead to instant speciation especially in plants b/c polyploid individuals can no longer reproduce with their original diploid population, creating a reproductive barrier

• 2 types: Autopolyploidy where indiv inherits multiple chrom sets from same species, and allopolyploidy where chrom sets come from diff species through hybridization

• Since polyploids can usually self fertilize or reproduce with other polyploids they form a new species quickly

• ex: wheat where hybridization and chrom duplication leads to diff species

Predict what may happen when 2 divergent populations come into contact again under various circumstances  

1. Fusion (re-merging into 1 species)

   • If the populations haven’t diverged too much they may still interbreed and exchange genes freely

   • Over time, gen diffs disappear and they become one species again

   • ex: 2 fish pops in a lake were sep by envt changes but later mixed again with no reproductive barriers

2. Reinforcement of divergence (stronger rep barriers)

   • If hybrids b/w pops are weak/less fit, natural selection will favor traits that prevent intebreeding b/w the pops

   • This strengthens prezygotic barriers (behavioral or temporal isolation) leading to full speciation

   • ex: 2 bird species that develop diff mating songs to prevent hybridization

3. Hybrid zones (stable or temporary hybridization)

   • There’s a well defined geographical area where hybridization occurs. May be temporary if hybrids are weak and pops continue diverging eventually stop intebreeding or stable if hybirds survive well, the area stays indefinfelty

   • ex: European toad maintains a hybrid zone where their ranges overlap

4. Creation of new species

   • If the populations have changed too much, they may be unable to mate at all, even if they meet again

   • Means speciation complete, they remain sep species

   • ex: diff species of fruit flies evolved on diff islands cant produce viable offspring

Describe population ecology  

• study of how pops of organisms change over time and interact with their env’t.

• It focues on pop size, density, distribution, growth rates, and interactions with other species

• Scientists use this field to understand how pops respond to env’t factors like resources, predators, and climate

• KEY ASPECTS

  • Pop density and size- total number of individuals in a pop and how closely they live together in an area

  • Pop distrubtuion- how indivudals are spread in a habitat

    • Clumped, uniform, or random

  • Pop growth and regulation- how pops increase or decrease based on birth rates, death rates, immigration, and emigration

    • Exponential growth when resources unlimited

    • logisitic growth when populations reach carrying capacity K limited by resources

  • Carrying capacity- max # of indivds that envt can support without degrading resources

  • ex: pond can only support certain # of fish before food becomes scarce

  • Factors Affecting Pop growth

    • Density depdendent factors- competiton, disease, predation. (INCREASE effect as population grows)

    • Density indepdent factors (affect pop regardless of size like natural disasters, climate change)

Explain why theres a trade off between survival and reproduction  

• Trade off=increasing one leads to decline of other

• Limited resources like time energy and nutrients which need to be strategically allocated to maximize their overall fitness (ability to survive and reproduce)

• Energy allocation: investing heavily in reproduction like producing a lot of offspring providing extensive parental care, can reduce energy available for maintain the organism’s own health and survival which can lead to a shorter lifespan or reduced abilty to withstand env’t stresses.

• ex: birds invest lots of time and energy into raising their offspring may cause a reduced lifespan or be less able to survive harsh conditions for themselves

• Natural selection favors individuals who are most effective at allocating resources to maximize their overall fitness, which often involves a balance between survival and reproduction. 

explain the formula used to calc pop growth  

Compare and contrast exponential and logistic pop growth  

	Exponential	Logisitic
Definition	Population grows at a constant rate w/out limiting factors	Population growth slows as it reaches carrying capacity due to limiting factors
Shape	J shaped curve	S shaped curve
Equation	DN/dt=rN	dN/dt=rN(K−N /K)
Rate of growth	Constant and unchecked	Slows as population nears carryinc capacity K
Carrying capacity K	Not considered	Growth stabilizes at K
Pop size	Grows indefinitely	Levels off at K
ex	Bacteria in an ideal env't with unlimited resources	Deer population in a forest with limited food and predators

Describe some methods for determining population abundance and type of species the method is used for  

Method	Description	Types of Species Used For
Quadrat Sampling	Quadrat placed randomly/systematically, and individuals are counted within it	Sessile organisms like plants, corals, and slow-moving invertebrates.
Transect Sampling	A line or belt is laid out across an area, and individuals are counted along it.	Plants, coral reefs, and some slow-moving animals.
Mark-Recapture	Individuals are captured, marked, released, and later recaptured to estimate population size using the Lincoln-Petersen Index.	Mobile animals like fish, mammals, birds, and insects.
eDNA Analysis	Environmental DNA is collected from water, soil, or air and analyzed for species presence.	Aquatic species (fish, amphibians), elusive species, and invasive species detection.

Describe how individuals within pops are distributed geographically  

• Clumped

  • If quality of habitat is patchy or organisms are social. Most common in nature

  • causes: uneven resource availbility (water, food)

  • Social behavioura

  • Protection from predators

  • ex: wolves in packs, fish, trees growing near water sources

• Uniform

  • Evenly spaced due to competition for resources, or territoriality in animals (nesting birds)

  • ex: penguins nesting at equal distances, desert shrubs competing for water

• Random

  • Position of each individual independent of the others

  • Causes: resources evenly aviable, no strong social or territorial behaviour

  • exL dandelions, trees in tropical rainforest

Graph and describe 3 general types of survivorship curves with examples of each 

Calc number of indivs in a pop from a mark recapture study. EXPLAIN formula instead.

Explain how and why the lnyx and hare populations cycle  

• Due to predator-prey interactions with hare populations driving fluctuations in lynx #’s

• When hare pops increase due to abundant fod, lynx pops also rise as they have more prey to consume

• However, as hares become overabundant they deplete their food sources, leading to starvation and a population decline

• When fewer hares avaible, lynx struggle to find food, causing their #’s to decrease as well

• As lynx pops drop, hare numbers slowly recover due to reduced predation and the cycle repeats aprox every 10 years

• This dynamic is influenced by factors like food avaibility, competition, disease, and env’t factors

Discuss the diff levels of ecological study and give examples  

Ecologists work at 5 main levels

1) Organismal

• Ecologists interested in the adaptations that enable individuals to live in specific habitats. These adaptations can be morphological, physiological, and behavioral.

• For instance, the Karner blue butterfly is considered a specialist because the females prefer to lay eggs on wild lupine. This preferential adaptation means that the Karner blue butterfly is highly dependent on the presence of wild lupine plants for its continued survival.

2) Population

• Ecologists ask q’s about how the # of individuals in a population change over time. A population is a group of the same species that lives in same area at same time.

• ex: the study of deer populations in a forest or the distribution of a specific plant species. 

• It examines how factors like birth rates, death rates, immigration, and emigration affect population size, density, and distribution. 

• It also considers how populations interact with their environment, including both living (biotic) and non-living (abiotic) factors. 

3) Community Ecology

• Community= species that interact with one another within a particular area

• Community ecologists study nature and consequencs of the interactions b/w species. They ask questions about predation, parasitism, competition, and how group of species respond to natural disasters.

• ex: A forest community comprises all the trees, the plant community, birds, deer, squirrels, foxes, fungi, insects, fish in forest rivers, and other local or seasonal species

4) Ecosystem Ecology

• Ecosystem= all organisms in a particular region, along with abiotic and biotic factors

• Study of how nutrients and energy move among organisms and b/w the atmosphere, soil, and water

• ex: a pond, where living organisms like fish and plants interact with non-living factors like sunlight and water, and the study of these interactions

5) Global Ecology

• Encompassed by the biosphere which is the thin zone surr Earth where all life exists

• Still growing field

• Focus on effects of humans on biosphere

Explain how the abiotic factors define a species niche  

• Niche= the specific role a species has in its environment, and how it obtains resources and survives

• Abiotic factors like soil, temperature, and water availability define a species niche by establishing the physical and chemical conditions where a species can survive, grow, and reproduce

• For example, cacti have adapted to desert envts with less water availability by developing thick, waxy skin and deep root systems to absorb water efficienty.

• In contrast, amphibians like frogs need moist environments b/c their skin plays s role in respiration making them sensitive to changes in temperature or humidity.

• Sunlight-for photosynthesis

• Mositure- organisms constantly lose water to evap and transpiration

• Temperature- defines range of species

• Also distribution- if water only avaible in one area, then more species will want to be in that area

• This shows how abiotic factors create environmental limits that shape the distribution, adaptations, and ecological roles of species in an ecosystem.

Describe the wallace line and species dispersal 

It’s a biogeorgraphical line that seperates species from Asia from ones in Australia.

• It was proposed by Wallace after he observed a sharp difference in animal species on either side of a narrow stretch of ocean b/w islands in Indonesia like Bali.

• Despite the islands being close together geographically, these islands have very different species because deep ocean trenches prevented the migration of many animals during periods of lower sea levels

• So the wallace line shows how physical barriers like mountains or water can limit species dispersal and lead to development of distinct ecosystems.

• Also shows how geography and history shape where species can travel, survive, and evolve

Compare and contrast any five natural biomes 

Biome	Climate	Vegetation	Biodiversity	Notable Adaptations
Tropical Rainforest	Hot and very wet year-round	Dense, multi-layered forest with tall trees	Extremely high; home to many species	Broad leaves for sunlight capture; fast nutrient cycling
Desert	Hot or cold, very dry	Sparse, drought-resistant plants (e.g., cacti)	Low; specialized organisms	Water storage in plants; nocturnal animals
Grassland	Moderate rainfall; dry seasons common	Mostly grasses, few trees	Moderate; many large herbivores	Fire-resistant plants; grazing animal herds
Temperature Forest	4 seasons, moderate-high rainfall	Deciduous trees (e.g., oak, maple), shrubs	High; diverse	Trees shed leaves in winter; animals hibernate
Tundra	Cold, dry; permafrost present	Mosses, lichens, low shrubs	Low; species adapted to extreme cold	Animals with thick fur; short growing seasons

What defines a biome  

• Regions characterized by distinct abiotic characteristics and dominant vegetation types

• Different ecosystems can belong to same biome

  • ex: deserts all over thew world

• Type of biome present depends on mostly climate-temp, moisture, sun, wind

• The nature of the biome that develops in a region is governed by average annual temp and precipation

Why are the tropics wet  

• B/c of how the sun heats the earth and how air moves in a pattern called the Hadley cell

• Near the equator, the suns rays hit directly, warming the land and ocean. This makes the air hot and full of moisture.

• Warm air rises and as it goes up it cools down and the water in the air turns into clouds and rain. This is why is rains so much in the tropics.

• Now the air that rose up moves away from the equator then sinks back down around 30 degree latitude.

• That sinking air is dry which is why many deserts like Sahara are found there

• This movement of air rising at the equator, moving outward, sinking, and then flowing back is called the Hadley Cell

• It helps explain why the tropics are wet

What is a hadley cell, how is it caused, and how does it affect climate  

• Near the equator, the suns rays hit directly, warming the land and ocean. This makes the air hot and full of moisture.

• Warm air rises and as it goes up it cools down and the water in the air turns into clouds and rain. This is why is rains so much in the tropics.

• Now the air that rose up moves away from the equator then sinks back down around 30 degree latitude.

• That sinking air is dry which is why many deserts like Sahara are found there

• This movement of air rising at the equator, moving outward, sinking, and then flowing back is called the Hadley Cell

• It helps explain why the equator is wet and the areas above and below it are dry.

Explain how interactions among species affect the distribution and abundance of interacting species 

1. Competition (-/-) interaction that lowers fitness of both indivs

   • When 2 species compete for the same limited resources (food, space, light) it can reduce the amount or limit the distribution of one or both species

   • Intraspecific competition occurs between members of the same species. – Because intraspecific competition for resources intensifies as a population’s density increases, it is a major cause of density-dependent growth.

   • •Interspecific competition occurs when members of different species use the same limiting resources.

   • ex: In rocky intertidal zones, 2 barnacle species compete for space. This means that one species has to live in the lower intertidal zone, which forces the other to live higher up where the other barnacle can’t survive due to dessication

2. Predation

   • Predator feeding on prey. This regulates prey populations and influences where they live to avoid predators

   • ex: sea otters eat sea urchins which in turn eat kelp. In areas with sea otters, urchin pops are controlled allowing kelp forests to thrive. Without otters, urchin #’s explode, kelp forests dissapear- affects abundance and distrib of all 3

3. Mutualism

   • Both species benefit, often increasing each other’s survival, abundance, or range

   • ex: bees and flowering plants. Bees get nectar, plants get pollinated. This interaction supports large bee pops and helps plants spread to new areas

4. Commensalism

   • One species benefits, other is unaffected. Allows benefiting species to thrive or expand its range

   • ex: Barnacles attach themselves to whales, using them for transport and access to food-rich waters, while the whales are not harmed or helped.

5. Parasitism

   • One benefits at expense of the other. Parasites can reduce host pop sizes or shift their distributions

   • ex: A fungus wiped out most American Chestnut trees in eastern North America. The fungus altered the forest composition and distribution/abundance of many species that depended on the chestnut

Describe the different interactions among species and how they act as agents of natural selection 

Interactions like competition, predation, parasitism, mutalism, and commensalism act as agents of natural selection

• in competition- traits that reduce competition like using a diff resource or being more efficient are favored. This drives NS by favoring indivs that are better competitors.

  • ex: galapagos finches evolve diff beak shapes to reduce comp by specializing in diff food types

• Predation drives evolution of defensive traits in prey and hunting adaptations in predators

• Parasitism- parasites evolve to be more effective at infecting and using hosts; hosts evolve defenses like immune response, or behaviours to avoid infection

  • ex: antibitoic resistance in bacteria

• Mutualism promotes traits that enhance cooperation and benefit both partners such as specialized pollination structures in plants and insects

• Commensalism can influence the evolution of traits in the benefiting species without affecting the other

  • ex: barnacles that attach to whales are selected for better adheisve structures

Predict what might happen if a new species is introduced to an area and competes with an existing species 

• Depending on how strong the comp is and how similar their resource needs are

• If the new species is more efficient at using resources, it may outcompete the native species, leading to a decline or local extinction of the native species.

  • Competitive exclusion-t two species cannot occupy the same niche in a habitat

  • EX: When 2 Paramecium types are grown individually in the lab, both species thrive. 

  • However, when they are placed together in the same culture with a limited amount of food they compete for food. 

  • This leads to the eventual decline and extinction of one species of paramecium in that environment. 

• Or the species might partition resources- for example by feeding at diff times/areas allowing them to coexist

• Sometimes, the introduction can disrupt entire ecosystems by altering food webs or habitat conditions. This would make new species invasive species.

Describe how resource partitioning can increase the number of species in an area 

• By reducing direct competition for the same resources

• It happens when species use resources in slightly diff ways, such as feeding at different times or using diff parts of a habitat, eating diff types/size of food

• This reduces overlap in their ecological niches and allows more species to live together without outcompeting each other

• ex: several species of warblers (small birds) can live in the same tree b/c each forages in a diff part. Some near the top, some in middle, others near bottom. By dividing the resource ( tree and its insects) they avoid direct comp and can all survive in the same area.

• Over time resource partitioning supports more biodversity as it allows more species to occupy similar habitats without driving each other to extinction

Compare and contrast constitutive and inducible defenses  

• BOTH- strategies organisms use to protect themselves from predators, herbivores, or pathogens

  Constitutive defense

  • Always present in organism regardless of threat

  • Built in and always active

  • can be structural like thorns, tough leaves, or chemicals like toxins, or bad tasting compounds

  • ex: a cactus has sharp thorns that are always there to deter herbivores

  Inducible defense

• produced or activated ONLY in response to a threat like being attacked

• saves energy when there is no threat present

• may take time to develop after the attack begins

• often a chemical like toxins, enzymes,

• ex: some plants produce bitter compounds after being chewed on by insects

• Tadpole enlarging body size in response to predator

• Good for occasional threats