AP Environmental Science Unit 2 Review (Everything you Need to Know!)

Summary

Mr. Smeads' AP Environmental Science review covers Unit 2, focusing on biodiversity's three levels: genetic, species, and ecosystem. He explains how biodiversity benefits ecosystems and humans through ecosystem services. The video also discusses island biogeography, ecological tolerance, natural ecosystem disturbances, and adaptations, like Homo habilis' opposable thumbs. It concludes with ecological succession and keystone species, emphasizing their roles in maintaining ecosystem balance.

Takeaways

• 🌿 Biodiversity encompasses three levels: genetic, species, and ecosystem diversity, each nested within the other.
• 🧬 Genetic diversity is crucial for species' adaptability to environmental changes, as it provides a range of traits that may help some individuals survive.
• 🌳 Species diversity, including species richness and evenness, is beneficial for ecosystems' resilience, as it ensures that if one species declines, others can fill the gap.
• 🌍 Ecosystem diversity is important for biomes' health, with higher diversity supporting more species and functions.
• 💰 Ecosystems provide valuable services to humans, known as ecosystem services, which are categorized into provisioning, supporting, regulating, and cultural services.
• 🏝 The theory of Island biogeography suggests that island species richness is influenced by proximity to the mainland and island size.
• 🕊 The dodo bird's extinction illustrates the vulnerability of specialist species on islands to invasive species and environmental changes.
• 🌡 Ecological tolerance refers to the range of conditions an organism can tolerate; genetic diversity can provide a buffer against environmental disturbances.
• 🌪 Natural events, such as seasonal changes, hurricanes, and forest fires, can disrupt ecosystems, but they also drive natural selection and adaptation.
• 🌎 Earth's climate naturally changes over tens of thousands of years due to variations in its orbit, known as Milankovitch Cycles, affecting sea levels and ecosystems.
• 🦍 Adaptations, like opposable thumbs in Homo habilis, provide a survival advantage and can lead to new species' evolution, demonstrating how genetic mutations can be advantageous.
• 🌲 Ecological succession involves the gradual change in species composition over time, with primary succession starting on bare rock and secondary succession following a disturbance.

Q & A

What is the main focus of Unit 2 in the AP Environmental Science course?

Unit 2 focuses on biodiversity, including the three levels of biodiversity and how biodiversity benefits ecosystems.

What are the three levels of biodiversity mentioned in the script?

The three levels of biodiversity are genetic biodiversity, species biodiversity, and ecosystem biodiversity.

How does genetic diversity benefit a species?

Genetic diversity benefits a species by increasing the likelihood that some members will have traits that allow them to adapt to environmental disturbances or changes.

What is species richness and how does it relate to species diversity?

Species richness is a measure of the total number of different species found in a given ecosystem. However, a higher species richness doesn't necessarily mean more species diversity; species evenness, which is the balance of population sizes, is also considered.

How does ecosystem biodiversity benefit biomes?

Ecosystem biodiversity, which refers to the variance in different ecosystems found in a given area, benefits biomes by supporting a greater species richness and providing a wider variety of habitats.

What are ecosystem services and how do they benefit humans?

Ecosystem services are the direct or indirect contributions of ecosystems to human well-being, including provisioning services (like wood for furniture), supporting services (like pollination), regulating services (like carbon sequestration), and cultural services (like tourism and recreation).

What is the theory of Island Biogeography and what are its two simple rules?

The theory of Island Biogeography suggests that the number of species on an island is related to its distance from the mainland and its size. The closer an island is to the mainland and the larger its area, the higher the species richness.

How does ecological tolerance relate to an organism's survival?

Ecological tolerance refers to the range of conditions an organism or species can tolerate before death or serious injury occurs. It's a measure of how much an organism can adapt to changes in its environment.

What are the three main levels of frequency for natural events that disturb ecosystems?

The three main levels of frequency for natural events that disturb ecosystems are periodic events (like seasons), episodic events (like hurricanes), and random events (like asteroid strikes).

How do Malankovic Cycles contribute to natural climate change?

Malankovic Cycles, which include changes in Earth's orbital eccentricity, axial precession, and obliquity, contribute to natural climate change by altering Earth's distance from the Sun and the tilt of the Northern Hemisphere towards the Sun.

What is the difference between primary and secondary ecological succession?

Primary succession occurs on a bare surface like bare rock, starting with pioneer species like moss and lichen, while secondary succession occurs in areas where soil is already present, often following a disturbance that clears out existing vegetation.

What is a keystone species and why is it important?

A keystone species is a species that has a disproportionately large effect on its ecosystem relative to its abundance. Removing a keystone species can cause the ecosystem to undergo dramatic changes or even collapse.

Outlines

00:00

🌿 Introduction to AP Environmental Science Unit 2

Mr. Smeads introduces the review of Unit 2 for the AP Environmental Science course and exam. He emphasizes the importance of understanding the concepts of biodiversity, which includes genetic, species, and ecosystem diversity. The instructor encourages students to practice their writing skills for the exam, specifically for the mini FRQs at the end of each unit. The video aims to help students think critically about environmental science topics and prepare for the AP exam.

05:01

🌍 Biodiversity and Its Impact on Ecosystems

This section delves into the concept of biodiversity, explaining the three levels: genetic, species, and ecosystem diversity. It discusses how genetic diversity within a population can help species adapt to environmental changes, while species diversity contributes to the health of an ecosystem by ensuring resilience against disturbances like disease. Ecosystem diversity, in turn, benefits entire biomes by supporting a variety of life forms. The paragraph also touches on the idea that biodiversity provides ecosystem services that are valuable to humans, such as provisioning, supporting, regulating, and cultural services.

10:02

🌱 Ecological Tolerance and Natural Ecosystem Disruptions

The paragraph explores ecological tolerance, which is the range of conditions an organism can tolerate before facing death or serious injury. It uses human body temperature as an example to illustrate the concept of optimal range and the zones of physiological stress and intolerance. The discussion extends to natural events that can disrupt ecosystems, categorized into periodic, episodic, and random events. It also covers the concept of Malankovitch Cycles, which are natural variations in Earth's orbit causing gradual climate change over tens of thousands of years, leading to changes in sea levels and ecosystems.

15:02

🦸‍♂️ Adaptations and Evolution in Ecosystems

This part of the script discusses how organisms adapt to environmental disturbances, using the opposable thumbs of Homo habilis as an example of an adaptation that provided a survival advantage. It explains that genetic diversity allows for a range of traits, which can lead to beneficial mutations like the opposable thumb that enabled early hominids to use tools more effectively. The paragraph also covers how species like Homo erectus adapted to new environmental conditions by evolving traits such as the ability to stand upright and use more efficient tools.

🌳 Ecological Succession and Keystone Species

The final section reviews ecological succession, distinguishing between primary and secondary succession. It describes the process by which pioneer species colonize bare or disturbed areas, leading to the development of soil and the eventual establishment of a climax community. The paragraph also introduces keystone species, which are crucial to the functioning of an ecosystem, and explains how the removal of such a species can lead to ecosystem collapse. Examples of keystone species include wolves and ecosystem engineers like beavers and mangroves, which create habitats that would not exist without them.

Keywords

💡Biodiversity

Biodiversity refers to the variety of life in an ecosystem, including the genetic variation within species, the variety of species themselves, and the ecosystems they form. In the video, it is emphasized as a critical concept with three levels: genetic, species, and ecosystem biodiversity. Biodiversity is crucial because it allows ecosystems to adapt to changes and disturbances, as illustrated by the example of sparrows with different beak sizes adapting to drought conditions.

💡Ecosystem Services

Ecosystem services are the benefits that humans obtain from ecosystems, such as food, water, and climate regulation. The video categorizes these into provisioning, supporting, regulating, and cultural services. For instance, the video explains how bees pollinate crops, which is a supporting service that benefits agriculture, or how trees sequester carbon dioxide, a regulating service that mitigates climate change.

💡Species Richness

Species richness is a measure of the number of different species within an ecosystem. The video uses this term to discuss biodiversity, pointing out that a higher species richness doesn't necessarily equate to higher biodiversity unless it is also balanced, leading to the concept of species evenness.

💡Species Evenness

Species evenness describes the distribution of population sizes among different species within an ecosystem. The video explains that evenness is important for ecosystem resilience, as it ensures that no single species dominates, thus protecting the ecosystem from the potential collapse due to disease or other disturbances.

💡Ecosystem Diversity

Ecosystem diversity refers to the variety of ecosystems within a given area. The video contrasts tropical rainforests, which have high ecosystem diversity, with deserts, which have low diversity. This diversity is beneficial as it supports a greater number of species and contributes to the overall health of biomes.

💡Island Biogeography

Island biogeography is a theory that explains the distribution of species on islands based on factors like distance from the mainland and island size. The video simplifies this concept by stating that closer islands have higher species richness due to easier migration, and larger islands can support more species due to greater habitat diversity.

💡Ecological Tolerance

Ecological tolerance is the range of environmental conditions that a species can tolerate before experiencing stress or death. The video uses human body temperature as an example, explaining that individuals have an optimal range for survival and that genetic diversity can provide a buffer against environmental changes by allowing some individuals to have a wider tolerance range.

💡Adaptation

Adaptation is a process by which species evolve to better survive in their environment. The video discusses how genetic mutations, like the opposable thumbs in Homo habilis, provided an energetic advantage that led to their survival and reproduction. This concept is central to understanding how species evolve in response to environmental changes.

💡Ecological Succession

Ecological succession is the process by which ecosystems change over time, either through primary succession (starting from bare rock) or secondary succession (after a disturbance). The video describes how pioneer species initiate this process, followed by a series of changes that lead to a climax community, which is a stable and mature ecosystem.

💡Keystone Species

A keystone species is one that has a disproportionately large effect on its ecosystem relative to its abundance. The video uses wolves as an example, explaining that their presence can prevent overgrazing by deer, which in turn maintains the health of the ecosystem. The removal of a keystone species can lead to ecosystem collapse.

Highlights

Introduction to Unit 2 of the AP Environmental Science course and exam preparation.

Emphasis on the importance of understanding the concepts in Unit 2 for the AP exam.

The necessity of practicing the writing style required for the AP Environmental Science exam.

Overview of biodiversity as the first topic in Unit 2, including its definition and importance.

Explanation of the three levels of biodiversity: genetic, species, and ecosystem.

The nested relationship between the levels of biodiversity and their benefits.

Discussion on genetic diversity and its role in species adaptation to environmental changes.

Species diversity and its measurement through species richness and evenness.

The concept of ecosystem biodiversity and its impact on biomes.

Introduction to ecosystem services and their categorization into four key groups.

Examples of how ecosystem services benefit humans financially.

The impact of human activities on disrupting ecosystem services, using the Deepwater Horizon oil spill as an example.

Introduction to the theory of Island Biogeography and its two simple rules.

The relationship between island distance from the mainland and species richness.

The relationship between island size and species richness.

The vulnerability of specialist species on islands to invasive species.

The concept of ecological tolerance and its importance for species survival.

The role of genetic diversity in allowing species to adapt to environmental disturbances.

Natural events that cause ecosystem disturbances, including periodic, episodic, and random events.

The Malankovitch Cycles and their influence on Earth's climate and sea levels.

Adaptation as a response to natural ecosystem disturbances, exemplified by Homo habilis and opposable thumbs.

The process of ecological succession, including primary and secondary succession.

The role of keystone species in maintaining ecosystem stability.

Conclusion of Unit 2 review and encouragement for students to think critically and apply their knowledge.

Transcripts

hey everybody it's Mr smeads and today

we're going to be reviewing unit 2 of

the AP environmental science course and

exam if you're ready to think like a

mountain and write like a scholar let's

get started before we go any further

with unit 2 today make sure you've got

your ultimate review packet study guide

printed out and ready to go as we go

through this video you want to answer

the practice questions make sure that

you really understand the concepts that

are covered in unit 2. that exam I may

is just too tough to go into without

practicing the writing style that you

need in Apes so make sure you're

practicing with the mini frqs at the end

of each unit so on we go into unit 2

with a short but sweet look at

biodiversity many of these Concepts

would be familiar already from your

biology classes so if you want to see

where we cover specific Concepts make

sure to take a look at the video time

stamps here that way you can pop down to

those sections if you just need A Brief

Review now the first Topic in unit 2 is

biodiversity and it's one that students

think they understand but often don't

fully grasp and that's because the basic

definition is really simple it's just

the diversity of different life forms

found in an ecosystem but what we really

need to make sure we have down are the

three different levels of biodiversity

and why biodiversity is so beneficial

remember that the three levels of

biodiversity are genetic biodiversity

ecosystem biodiversity and species

biodiversity and these three levels are

nested within each other which helps us

remember why they're so beneficial

genetic diversity is the variance of

genes or traits found within individuals

of a population so high genetic

diversity or a wide range of different

traits is beneficial to species because

it increases the likelihood that if

there's an environmental disturbance or

a change in that ecosystem some of the

members will have genes or traits that

allow them to adapt so if you have a

population of sparrows and then there's

a drought that causes the seeds they eat

to become dry and harder High genetic

diversity in that population will

increase the likelihood that some of

them have bigger beaks that can still

crack those harder seeds open species

diversity is the diversity of different

types of organisms found in an ecosystem

now there's a really simple way to

measure and there's a more complex way

to measure it now the easy way to

measure is species richness this is just

a count of the total number of different

species found in a given ecosystem but a

higher species richness doesn't

necessarily mean that an ecosystem has

more species diversity we also want to

consider what's called species evenness

this is the distribution or the balance

of the population sizes of all the

different populations present so if we

look at this diagram we can see that

even though the two forests have the

same species richness Force number one

will have a higher species evenness now

this higher species evenness is

beneficial to the whole ecosystem of

forest number one that's because if

there were disease that spread among one

deciduous tree species in that ecosystem

there would still be plenty of conifers

or other deciduous species to repopulate

that Forest now if the same disease were

to strike in force number two that force

would have the potential to lose 70

percent of its tree cover if this

dominant tree species were susceptible

to that disease now that would devastate

the forest in a way that Forest number

one wouldn't be so just like genetic

diversity is beneficial to populations

and species diversity is beneficial to

ecosystems ecosystem biodiversity is

beneficial to entire biomes an ecosystem

diversity just refers to the variance in

the different ecosystems found in a

given area so the tropical rainforest

would have a really high ecosystem

diversity you're going to find Rivers

different types of tree stands Edge

habitats where a forest meets an open

area whereas a desert biome is going to

have a lot lower ecosystem diversity and

be able to support less species richness

because of that so now that we

understand why biodiversity benefits

ecosystems let's take a look at how

ecosystems benefit humans by making us

richer now I know what you're probably

thinking wait uh what is going on here

the vegan bike riding carbon emission

cutting environmental science teacher is

talking about exploiting nature for

money but remember many of the things

that we attach monetary value to

ultimately come directly from or are

dependent on the natural function of

ecosystems now these Financial benefits

that we get from ecosystems are called

ecosystem services and in Apes we

categorize the different type of

services into four key categories

provisioning services are the easiest to

remember and that's because these are

things provided directly to us by

natural ecosystems examples would

include things like wood for furniture

or houses that can be harvested and sold

for a profit supporting services are

processes done by ecosystems that

support a valuable Human Action such as

agriculture for example insects like

bees and moths May pollinate a farmer's

crops increasing the amount of produce

they can sell now the farmer could still

produce some food without those

pollinators but not nearly as much so

their profits or their yields are

supported by those pollinators

regulating Services refer to the fact

that ecosystems often regulate or

stabilize climate or other environmental

factors which saves US money from having

to pay to clean up unstable conditions

so the fact that trees sequester carbon

dioxide can save us money because it

reduces some of the expensive

consequences of climate change this

could be things such as droughts which

damage Farmers crops or storm damage

which could damage your home and finally

we have cultural Services which are the

recreational or intellectual benefits we

get from nature so a tourist going to

visit the Grand Canyon is going to pay a

park fee and stay at a local hotel which

generates Revenue scientists research

ecosystems and they might write books or

reports that lead to valuable products

being created in addition to being able

to identify the four categories of

ecosystem Services we also want to

understand how humans can disrupt

ecosystem services so great example

would be drilling for and transporting

crude oil so when the deep water Horizon

oil spill happened in the Gulf Coast of

Mexico a ton of ecosystem Services were

disrupted fishermen weren't able to

catch as many fish and their profits

suffered mangrove swamps and salt

grasses died which destabilized the

coastline and led to more storm damage

and the tourism industry was impacted as

beaches were covered in oil and tourists

were less likely to come visit and on

topic 2.3 we'll take a look at the

theory of Island biogeography this can

sound like a super complex topic but it

really just boils down to two Simple

Rules so let's say we have two islands

of equal size but one is closer to the

mainland than the other the closer

Island would be likely to have a higher

species richness just because there are

more species capable of migrating to the

island from the mainland the further

away from the mainland island is the

fewer species that are able to fly or

swim there so if we plot distance from

the mainland and number of species on a

graph we'll see an inverse relationship

between the two now if we look at two

islands that are the same distance from

the mainland the larger Island would be

likely to have a higher species richness

this is due to the fact that it's going

to have a higher ecosystem or habitat

diversity with more space there's a

greater variety of Landscapes like

forests or grasslands or ponds this

means that we can have a wider variety

of plant and animal species supported in

this ecosystem so if we plot Island area

and number of species on a graph we'll

see a direct relationship between the

two as the Island area increases so too

does the number of species supported by

this island we also need to remember

that Island ecosystems are somewhat

unique in that they're going to offer a

narrow range of food and habitat choices

to species this often leads to really

specific adaptations where species are

adapted to the conditions of these

narrow food and habitat choices take the

dodo bird for example this large

flightless bird species evolved from a

member of the pigeon family some 20

million years ago now because it only

inhabited the small island of Mauritius

it didn't have a lot of competition from

other herbivores or pressure from

predators this led to an increasing body

size and the loss of flight because a

small flight worthy body wasn't

advantageous anymore without competitors

or carnivores to fly away from and the

problem for these highly specialized

species is that because they're uniquely

adapted to these narrow conditions

they're often unable to adapt to or

compete with invasive species that show

up on their Island and this is precisely

what happened to the dodo bird when the

most invasive species of all time showed

up on their Island the humans now

without getting too graphic suffice it

to say that the dodo bird is not around

anymore and the big takeaway here is

that islands are going to have a higher

percentage of specialist species than

the mainland and those specialist

species are going to be more vulnerable

to invasives because they're so uniquely

adapted to the narrow conditions of

those islands

dodo brain

so as good as DW is at cooking Arthur

this one doesn't really add up

definitely didn't go extinct because

they were dumb they just evolved on an

island with no natural predators and so

they weren't afraid of the humans when

they showed up so maybe the real dodo

brains were the Dutch Sailors who hunted

dodos at a way faster rate than they

could repopulate and somehow didn't

think that would lead them to Extinction

so moving on from islands and dodo

brains we'll take a look at a really

simple concept called ecological

tolerance this just refers to the range

of conditions an organism or species can

tolerate before death or Serious injury

ensues so let's start with an easy

example that we're all really familiar

with and that's human body temperature

most of us are sitting somewhere between

a comfortable 97 and 99 degrees

Fahrenheit now there are a few outliers

with especially high or low body

temperatures and this is a great example

of genetic diversity but in general

humans have an optimal range for body

temperature of about 97 degrees to 99

degrees this is the range where bodies

function most optimally we're able to

survive grow and develop so what happens

if an organism moves outside of its

optimal range the first thing that

happens is it enters What's called the

zone of physiological stress so let's

return turn to this human body

temperature example if your body goes

above 99.5 or below 95 degrees you're

going to enter a stressed physiological

State you're not going to think or move

as quickly as you would normally and

you're not going to be able to remain

here for long without serious

consequences if you move even further

from the optimal range so above 106

degrees or below 86 degrees you're going

to leave the zone of physiological

stress and enter what we call the zone

of intolerance which quickly leads to

death now this is a great time to review

why genetic diversity is so important

there's a general range of tolerance

that all the members of a given species

share such as this optimal range for

human body temperature but there's also

some variation between individuals and

that's due to genetic diversity so some

individuals may have a wider range of

tolerance or a wider optimal range than

others and this is how genetic diversity

can act as sort of a buffer against

environmental disturbance so if the

environmental conditions of a population

change such as the temperature or the pH

of their environment some of the members

are going to have a wider range of

tolerance due to genetic diversity they

can survive the environmental change and

pass on these tolerant genes to their

offspring which allows a new population

to evolve that is now adapted to this

new condition speaking of environmental

disturbances we need to take a minute to

review the non-human or natural events

that can disturb ecosystems now before

you start thinking I'm letting humans

off the hook for disturbing the

environment with five whole units

dedicated to the different ways that we

impact the environment so don't worry

but for natural events that cause

ecosystem disruptions there's three main

levels of frequency we need to

understand first we have periodic events

these are things like rainy Seasons or

dry seasons that happen with some

regularity then we have episodic events

these occur less regularly but they're

still occurring with some regularity

especially when the environmental

conditions are right great examples of

these events would be hurricanes and

forest fires they don't happen super

regularly but they are more likely to

occur when the environmental conditions

are right and finally we have random

events which as their name implies occur

with no Rhyme or Reason whatsoever these

are things like an asteroid striking

Earth or volcano erupting however

ecosystems can also will be disrupted by

slow gradual changes in Earth's climate

over time the reason Earth's climate

change is naturally over time is because

the orbit that the Earth takes around

the Sun changes naturally over time the

first way that the Earth's orbit around

the sun changes is called eccentricity

this refers to the shape of the orbital

path that the Earth takes around the Sun

sometimes this shape brings the earth a

bit closer to the Sun in its orbit and

sometimes a bit further away the second

is called axial precession where how

much the Earth wobbles on its axis and

the third is the change in Earth's

obliquity or tilt we call these

variations in Earth's orbit malankovic

Cycles since each of these Cycles

happens with a regular frequency they

produce regular changes in Earth's

climate as a result notice on the x-axis

of these graphs that we're talking about

cycles that unfold over tens of

thousands of years so they produce

really gradual climate change not the

type of change we're seeing right now

which is easily observable in one human

lifetime what scientists have learned

from lining up the timing of these

malakovich Cycles with ice core

temperature data is that these Cycles

impact the temperature versus climate by

bringing closer or further away from the

Sun or tilting the Northern Hemisphere

closer or further away from the Sun now

don't worry about understanding the

intricacies of the malakovich Cycles you

don't need to go this in depth in Apes

what you do need to know is that earth's

climate changes naturally over time over

the course of tens of thousands of years

as Earth's orbit brings Earth either

closer or further away from the Sun or

tilts the Northern Hemisphere closer or

further away from the Sun the other

thing we need to remember about Earth's

natural gradual cycling of climate

change is that it causes a change in sea

level as we can see here there's a

really clear link when we look at the

last 400 000 years worth of data on

global temperature and sea level during

periods where earth's climate is warmer

sea level rises due to both the melting

of glacial and polar ice sheets and also

the thermal expansion of water molecules

in the ocean now in the context of

ecosystems let's think about what this

rise in sea level and change in

temperature can mean low-lying Coastal

ecosystems like estuaries may be

completely flooded and may disappear

during periods of high sea level shallow

ocean waters that provide tons of

sunlight to Coral Reef ecosystems may

become deeper and light may not

penetrate to the bottom which completely

changes those ecosystems these are the

types of ecosystem disturbances we need

to think about when we're talking about

this slow gradual cycle of natural

climate change now you may be thinking

poor manatees or Coral or other species

that are impacted by natural ecosystem

disturbance but don't forget that

ecosystems and organisms can adapt in

fact every species on Earth is the

result of adaptation on the part of some

ancestor species forced to change based

on natural ecosystem disturbances and

environmental upheaval so the next time

you catch a dub in Call of Duty or

fortnite don't forget to thank homo

habulous for those opposable thumbs in

all seriousness though let's take a

closer look at how this trait of

opposable thumbs may have Arisen in

ancestors of Homo habilis first we need

to think back to the genetic diversity

concept that we reviewed in the

beginning of this video because of

genetic diversity there's a range of

traits even thumb muscle arrangement in

all members of a population so some

early members of the homo habulous

species randomly developed an new thumb

muscle Arrangement roughly 2 million

years ago this thumb muscle Arrangement

allowed for a tighter more nuanced grip

that ultimately led to the ability to

manipulate and create stone tools now

the prevailing scientific consensus is

that this new thumb muscle Arrangement

enabled homo habulous to create and

wield more efficient stone tools for

cracking open animal bones this gained

them access to the energy-rich marrow

inside and gave them a huge energetical

advantage over similar primates that

didn't have this same access to bone

marrow now because of this big

energetical Advantage the opposable

thumbs brought members that had this

adaptation survived longer due to access

to more marrow and passed on those

traits to more offspring an adaptation

is just a genetic mutation like a new

thumb muscle Arrangement that gives an

organism a higher likelihood of

surviving and reproducing as we wrap up

our review of adaptations here the

important thing to remember is that

organisms are either able to adapt to

environmental disturbances or they're

unable to adapt to environmental

disturbances and then they go extinct

some of the environmental changes that

early hominids adapted to were moving

out of dense forests and into grasslands

in these new grassland conditions it

became advantageous to be able to stand

up so we see Homo erectus with the

ability to stand upright look around and

Survey the environment it was also

advantageous to be able to wield more

efficient tools to break open animal

bones to get more energy all of these

are great examples of adaptations that

allowed species like Homo habilis to

adapt to new environmental conditions

survive and pass those traits onto

Offspring and speaking of surviving look

at you surviving all the way to the end

of the unit 2 review as we wrap up our

review of ecosystems we'll review

ecological succession and keystone

species first of all we have to remember

that there are two types of ecological

succession that's primary succession and

secondary succession in primary

succession pioneer species like moss and

lichen start to colonize a bare rock

ecosystem when the wind transports their

seeds or their spores there now they're

able to grow on bare rock because they

can secrete acids which release the

nutrients and minerals they need from

The Rock through a process called

chemical weathering this chemical

weathering process combined with a death

and regrowth of the Moss and lichen

slowly lead to the formation of shallow

rocky soil this in turn allows other

pioneer species like grass wildflowers

and shrubs to colonize the area

eventually the continual death and

regrowth of these early successional

plants adds more and more organic matter

and depth to the soil this then enables

intermediate successional species like

shade intolerant fast-growing trees to

come and colonize the area over time

slower growing shade tolerant species of

trees like Oak and Maple grow up and

replace the intermediate successional

trees and trucks we call this community

that has progressed through these stages

of succession in climax community these

ecosystems typically have large amounts

of biomass and support a high species

richness secondary succession follows a

really similar progression of changes

with one key difference there's already

soil present instead of moss and lichen

being blown in by the wind and

colonizing bare rock you have pioneer

species like grass and wildflowers being

blown in by the wind and they're

colonizing Disturbed soil you see

secondary succession tends to take place

after a disturbance that clears out the

existing vegetation this could be a

forest fire a glacial Retreat or even

humans abandoning an agricultural field

the pioneer species in secondary

succession are still fast growing and

Sun tolerant and typically they have

their seeds dissers by either the wind

or by animals and finally we'll review

keystone species now remember a keystone

species is more than just an important

species every species has some level of

function in its ecosystem but a keystone

species is one that's so vital to its

ecosystem function that if it's removed

the entire ecosystem can collapse so if

we were to lose a keystone species like

wolves from a forest ecosystem the deer

and Alchemy overpopulate this would lead

to over grazing of the vegetation of

that ecosystem and this could be so

intense that other organisms would lose

those trees and food and habitat

resources this could even lead to the

reshaping of the landscape as the tree's

roots would no longer be there to hold

the soil intact and the banks of rivers

might erode without those plants

stabilizing the soil along the banks

other keystone species examples include

ecosystem Engineers like beavers and man

groceries these species shaped landscape

so dramatically that they create

habitats That Couldn't exist without

them the mangrove swamp would be

impossible without those stilt-like

roots of the mangrove tree and the

Beaver Pond would be impossible without

the Beaver Dam and that is unit two

in the books hopefully you feel like the

vocabulary richest of your mind has

increased maybe you even have some fast

growing mid-successional Apes ideas

taking root in the soil of your brain

thanks for watching today ape Scholars

as always think like a mountain and

write like a scholar