Ecological Succession: Change is Good - Crash Course Ecology #6

  Рет қаралды 1,173,564

CrashCourse

CrashCourse

Күн бұрын

Пікірлер: 656
@AfkOptic
@AfkOptic Жыл бұрын
Station 5 answers for me. (Take this with a grain of salt) 1. Orderly. 2. No competition. 3. Plants, they make the ecosystem habitable. (Not sure about this one) 4. Never stops because it can’t. (Or this one) 5. Weather. 6. Probabilities, not certainties 7. High biodiversity.
@Tay_and_Hay
@Tay_and_Hay Жыл бұрын
For biology ppl station 5: 1. Predictable and orderly 2. There is not competition, so pioneer species like prokaryotes and non-vascular plants can live there successfully 3. Plants because without plants, people and animals won’t survive 4. Succession never stops because change never stops 5. Stochasticity (randomness) prevents us from being able to tell what it will look like in the future 6. Probabilities not certainties 7. If it has high biodiversity Hope this helped!🤍
@TegaOnYT
@TegaOnYT Жыл бұрын
Thanks, may God bless you 🙏
@Ech0TheCerva
@Ech0TheCerva Жыл бұрын
Oh my freaking god you are a GODDESS THANK YOU SO FREAKING MUCH
@kaylahayward4267
@kaylahayward4267 Жыл бұрын
I love you sm
@larz-barz
@larz-barz Жыл бұрын
❤tysm
@tripwanna
@tripwanna Жыл бұрын
I literally love you thanks
@ceizmendi
@ceizmendi 10 жыл бұрын
At about 2:00 min, Hank gives an example of primary succession that I believe is incorrect: forest fire. All the other examples he gives could remove or destroy the organic matter in the soil, but forest fires definitely don't. By definition that's secondary succession. Primary succession has to be starting from bare rock, whether solid bedrock, crushed-up sand, or particle sizes in-between.
@gm-fm9rd
@gm-fm9rd 9 жыл бұрын
+ceizmendi came here to be sure someone said that. Often, a forest fire leaves root and seed stock.
@hackedbyanasshole5397
@hackedbyanasshole5397 7 жыл бұрын
Wow. I'm not the only nerd watching. MARVELOUS!
@ananyanath855
@ananyanath855 6 жыл бұрын
came down here to comment exactly that. Actually almost all of the examples he gave were of secondary succession since the main condition for primary succession is that it should be an area that has never been inhabited before
@magnuspeacock5857
@magnuspeacock5857 6 жыл бұрын
I'm glad that some people are nerdy enough to notice that.
@magdaleneochola4179
@magdaleneochola4179 5 жыл бұрын
@@ananyanath855 How does that work tho?? Cuz if the area has never been inhabited before how will anything grow from it. Plus how do you have an inhabitable area. There has to be something. Maybe some kind of bacteria or a species of plants that hasnt been discovered yet. Idk. Im just a 9th grader trying to study for a big biology exam
@jadetheshade
@jadetheshade 6 жыл бұрын
i thought "niche" was pronounced "neesh"
@rainer_uncrowned
@rainer_uncrowned 6 жыл бұрын
It is, but ya know Americans... they be crazy!
@y2kona
@y2kona 5 жыл бұрын
R S what
@Makeupby.garima
@Makeupby.garima 5 жыл бұрын
@@rainer_uncrowned lmao true
@rainer_uncrowned
@rainer_uncrowned 5 жыл бұрын
@@y2kona because Americans pronounce it differently.
@heyimmashark9030
@heyimmashark9030 5 жыл бұрын
rainer I’m American and I say “neesh”
@MaiCohWolf
@MaiCohWolf 6 жыл бұрын
I'm a ranger in Yellowstone... it wasn't a single lightning bolt that caused the 1988 fires. It was 42 strikes, along with 9 or so human-caused fires that coalesced into several massive fires that swept through the park. But Hank's definitely right about it burning so bad because it hadn't been allowed to burn in a long time -- 36% of the park was torched. We learned a ton about fire management from the event. Love this channel tho, and thanks so much for the awesome ecology series, Crash Course! :)
@StephObsessed
@StephObsessed 11 жыл бұрын
Hank, you are the reason why I have an A in Biology.
@helllocathy
@helllocathy 8 жыл бұрын
Studying for my environmental science final exams...
@EnderFlames
@EnderFlames 8 жыл бұрын
catwang same here
@hayleyf9438
@hayleyf9438 5 жыл бұрын
Me
@nowlun
@nowlun 5 жыл бұрын
YEP
@abee948
@abee948 4 жыл бұрын
catwang same lmao but quarantine style
@user-yh7br7oo4z
@user-yh7br7oo4z 4 жыл бұрын
I’m watching this for online school during Corona-virus. ( I hate my school district!!!!!😠)
@mayrana7645
@mayrana7645 4 жыл бұрын
V sameee
@thetruth830
@thetruth830 4 жыл бұрын
Same
@alexispaige772
@alexispaige772 4 жыл бұрын
Same
@user-yh7br7oo4z
@user-yh7br7oo4z 4 жыл бұрын
Teresa Cruz Cuevas ...Fort Bend?
@gilbbyoutdoors
@gilbbyoutdoors 4 жыл бұрын
Ik how you feel these texas schools be tripping all knowledge I've gained about biology and ecology have come from crash course. I personally believe that Crash Course is better that learning at school anyways
@mycominer
@mycominer 12 жыл бұрын
Not only did you just help me understand ecology better, I think you just helped me to understand the economy better as well.
@chiblast100x
@chiblast100x 12 жыл бұрын
I'm really loving these last few episodes, they cover many of the topic in ecology that I've had the most fascination with over the longest time.
@rayamoooooo685
@rayamoooooo685 5 жыл бұрын
06:31 "some yeehaw might rent himself a backhoe one week and clear himself a lil' patch of heaven" 😂
@skimperplayz1448
@skimperplayz1448 Жыл бұрын
When you've memorized that theme song, you know you've been preparing hard for that bio final 😂😂🤣🤣 I love this course. Hope Hank recovers from cancer 🙏🏻🙏🏻🙏🏻
@TerenceClark
@TerenceClark 10 жыл бұрын
I loved watching the succession activities of the cottonwoods on pavement where I went to school. It took the maintenance folks months to clean it all. And by the time they did, the seeds, which couldn't grow on their own, had nevertheless built out a "soil" matrix of sorts that had started to support mosses and clovers in short order. Like it or not,our landscapes are just a new, weird sort of niche for nature to dig in to.
@laurelpais
@laurelpais 10 жыл бұрын
just watched this in my Biology class, really happy our teacher showed us this
@User-to7nb
@User-to7nb 10 жыл бұрын
I WATCH THESE VIDEOS FOR NO REASON AND TODAY WE ACTUALLY LEARNED SOME OF IT!!!! *gasp* thankyouuuu hank
@AmakunaiChan
@AmakunaiChan 12 жыл бұрын
CrashCourse team, from the bottom left chamber of my heart, thank you for explaining what I wish school had at junior high level. Ecology is complexly wonderful!
@samuelfeder9764
@samuelfeder9764 11 жыл бұрын
Could you make a whole video on soil creation and what makes a good soil? I personally think that would be really interesting , especially as we constantly hear that soils are lost to deserts ect. but most people don't seem to know how long it would take to creat new ones...
@actress223
@actress223 2 жыл бұрын
I teach outdoor education to middle school kids and it's videos like this that make my job as a teacher just a little easier (:
@andrewbusch5119
@andrewbusch5119 9 жыл бұрын
Seriously man. You would help twice as many people if you would just slightly modify that tempo. Love you though. - Native English Speaker
@bitodd
@bitodd 12 жыл бұрын
"Change is the only constant." Planck chuckles.
@bengoulet11
@bengoulet11 12 жыл бұрын
literally went on youtube to distract myself from studying ecological succession.. thanks Hank
@JazzyAnne
@JazzyAnne 9 жыл бұрын
Thank you for this! This helped me understand this school topic more :)
@friendlps9249
@friendlps9249 9 жыл бұрын
OMG I luv your videos
@sahejpreetdhillon3581
@sahejpreetdhillon3581 8 жыл бұрын
I love your videos Jazzy! I'm glad we both find Crash course useful! :)
@wildebt
@wildebt 6 жыл бұрын
This channel rocks! Thanks for helping me prepare casually for grad school applications.. I am moving from an undergrad degree in biochem to hopefully a graduate degree in ecology or conservation biology!
@thecoworker12345
@thecoworker12345 12 жыл бұрын
Every time I hear that theme song, chills
@rayzars
@rayzars 12 жыл бұрын
Just over ONE YEAR and just under 100 videos!!! Thank you crash course!!
@magdaleneochola4179
@magdaleneochola4179 5 жыл бұрын
Love that he is hilarious so that i can laugh while still studying 4 my exam 2morrow that i will hopefully not fail.
@leannyly
@leannyly 8 жыл бұрын
"Niche" rhymes with "quiche"...
@LuisSierra42
@LuisSierra42 8 жыл бұрын
Very smart observation, it blows my mind
@Ali-cr9ex
@Ali-cr9ex 7 жыл бұрын
very funny observation i laughed historically and came a little
@KaziCare
@KaziCare 7 жыл бұрын
Actually it doesnt vs
@CrazyGamer-xi8rf
@CrazyGamer-xi8rf 7 жыл бұрын
Rat eaters
@grammy9284
@grammy9284 7 жыл бұрын
it doesn't.
@steelshade
@steelshade 12 жыл бұрын
Hank: "There is one tremendous advantage to desolate waste lands..." Me: "No competition." Hank: "... no competition." I totally called it. I must be learning something. Thanks, Hank!
@LaughingMan44
@LaughingMan44 12 жыл бұрын
Wow, it's funny how this concept of change being the only constant and disturbances being good for an ecosystem can also be applied to personal life. Philosophy derived from science always has the deepest impact for me.
@NexxZt
@NexxZt 7 жыл бұрын
Thanks dude! Reading for my exams on tuesday, and this video is a whole lot better than what my book and teacher has to offer :)
@marekcoleman1890
@marekcoleman1890 12 жыл бұрын
I learnt all about this in uni and i think he summed up the concept quite well. there is still a lot more detail that can be found about this such as how surveys of ecosystems support the intermediate disturbance hypothesis. It was really interesting when we investigated how the aboriginal communities applied this intermediate disturbance although they didn't do it with the intention of the increased biodiversity it causes. Ecology is just really interesting.
@kokopelli314
@kokopelli314 5 жыл бұрын
One of the better explanations. Resilient ecologies are functionally adapted to respond to disturbance within specific time and energy scales. Spruce Budworm cycles within Boreal forests are a good example showing the fallacy of characterizing a stage of adaptive community response as a "Climax" community.
@vikasvashisth6631
@vikasvashisth6631 10 жыл бұрын
A NICE ILLUSTRATION OF PEDAGOGIC SKILLS..FAST NARRATION IS A WAY TO KEEP THE LISTENER ATTENTIVE ALL TIMES WHICH LEADS TO MORE ABSORPTION IN LESSER TIME !
@MeganMcken
@MeganMcken 12 жыл бұрын
i took an ecology course in first year uni and that's one of the few things i remember. Spiders being one of the first animals to colonize in disturbed areas.
@toxiPsychotic
@toxiPsychotic 11 жыл бұрын
Another thing that comes to mind is something i think i remember john saying about language. Basically, the purpose of language is to ensure that communication is clear and understandable to everyone involved. People who are grammar or spelling or punctuation nazis don't actually help this much, because they tend to point out errors that are so minor that they have no influence on the clarity of discourse. Sometimes they're even wrong, confusing errors for regional differences and such.
@nathanoliver9237
@nathanoliver9237 12 жыл бұрын
It's like an economy depressions and booms come and go. And the metaphor in which humans trying to interrupt change makes it worse disturbance.
@LittleLaurey
@LittleLaurey 12 жыл бұрын
I came on KZbin to procrastinate and ended up revising for my A2 biology exam anyway. Good job Hank
@unvergebeneid
@unvergebeneid 12 жыл бұрын
This would have been a good opportunity to highlight some recent research that uses recovery time after disturbances to predict overall resilience and thus time left for the ecosystem to collapse completely under the weight of humanity. It's a general rule for many systems that the quicker they recover from small disturbances, the more resilient they are to large disturbances.
@FallenEpic
@FallenEpic 12 жыл бұрын
Here in Washington State we get to see what happens in primary succession first hand in the land that got completely wiped out by the Mount Saint Helens eruption. I recommend looking up that environment and seeing how it recovered and changed. Although that's the 30 years later mark, not 1,000 years later maker.
@Nick-li8ol
@Nick-li8ol 9 жыл бұрын
Man i wish you were my ecology lecturer.
@MogofWar
@MogofWar 12 жыл бұрын
Well! Good luck on that.You have your work cut out for you and plenty of time to do it. That's a winning combination you should never take for granted.
@Germanbiscuts
@Germanbiscuts 12 жыл бұрын
I'm glad I found someone who knew who this was....... it gets a bit eerie after awhile though.
@Mormodes
@Mormodes 12 жыл бұрын
No, I understand that, my question calls for preventing fires in a way that allows small portions to burn rather than trying to prevent ALL fires from occurring. It would be like having patches of farmland separated by a large enough distance that the fire could not spread from one spot to the other.
@haroonrasheed11
@haroonrasheed11 4 жыл бұрын
studying for my forestry and woodland test, really helpful video. Thankyou!
@marymartinangel5988
@marymartinangel5988 8 жыл бұрын
Wow! This was very helpful! I am a student of wildlife management and doing an essay on succession. Thanks!
@SuperRat420
@SuperRat420 12 жыл бұрын
Whenever we're finished with this or literature, Crashcourse film would be really interesting.
@megafire7
@megafire7 12 жыл бұрын
'Not every change is an improvement, but every improvement is a change.'
@leannabad3839
@leannabad3839 6 жыл бұрын
Came here because I watched Avengers: Infinity War and Thanos' plan reminded me of this.
@layanmahmoud8210
@layanmahmoud8210 10 жыл бұрын
omg i have midterms and this REALLY! HELPS
@khurramsheraz4419
@khurramsheraz4419 6 жыл бұрын
This guy literally helped me graduate.
@Thorin1300
@Thorin1300 12 жыл бұрын
I haven't Been to Yellowstone but i have been to Mt. Saint Helens. The cool thing about MT saint helens is that you can go from one level of disturbance a different one by walking to and fro from the mountain. The closer areas having been completely destroyed after the eruption while farther areas just having fires or toppled trees and all the ash problem. Ecologist are probably having a lot of fun up there great vid Hank Look forward to the next one DFTBA
@kylieveale6462
@kylieveale6462 4 жыл бұрын
great examples and definitions that helped confusion and learning through online school due to COVID-19!
@Eman-wj8gq
@Eman-wj8gq 10 жыл бұрын
Hank you are the man. Thanks for making these videos so fun.
@TacticusPrime
@TacticusPrime 12 жыл бұрын
The REASON that the fire was so terrible in 1988 was BECAUSE fires had been prevented in Yellowstone for so long. For decades fires were conceived to be only bad for the ecosystem, so they were smothered quickly. Finally, there was just too much raw material available for the the fire, so it went crazy. It's not going to happen like that anymore BECAUSE we allow intermediate disturbance. That's the point Hank is trying to make.
@Onychoprion27
@Onychoprion27 12 жыл бұрын
Helens didn't take the area back to 'wiped out by an asteroid'. It didn't have to rebuild soils, which is why trees started re-growing almost immediately (secondary succession)
@kodznor5932
@kodznor5932 9 жыл бұрын
This answered all of my biology homework questionsssss, thanks :)
@Megan-ik2iq
@Megan-ik2iq 11 жыл бұрын
Fantastic series! Thank you for helping me study!
@abbiepanda9367
@abbiepanda9367 7 жыл бұрын
Have you ever noticed how life mirrors the earth? Like when there's a forest fire. Sometimes there's a disturbance and there's nothing you can do but watch everything burn down and die. It's horrible and sad but it's for good reason because the ashes are what allows things to rebuild. Often you must rebuild and it starts small like flowers, that may not seem like a big deal but eventually bigger things will grow and soon there will be something different but even more beautiful. Stay strong I love you.
@geerasnake7163
@geerasnake7163 4 жыл бұрын
Happy Birthday Mr.Ritt
@traehignight
@traehignight 2 жыл бұрын
Any Hudson students here? Or at least others who scanned a QR code?
@tadblackington1676
@tadblackington1676 5 жыл бұрын
You stated very sussinctly the problem with our models of succession, we are only talking about plants. Why? Animals exist and they can be great drivers of disturbance and biodiversity. The "battle" between vegetation and herbivores is a huge driver of biodiversity. The problem we have with it is that it changes the models of succession we need to have in our heads from linear to circular, ie Frans Vera's model.
@MrGuilhermeSilvano
@MrGuilhermeSilvano 12 жыл бұрын
"Now, here, you see, it takes all the running you cando, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast!" - Red Queen
@wbmtaverage
@wbmtaverage 12 жыл бұрын
You pretty much just explained a whole topic of the A level biology specification. With key terms and everything.
@Germanbiscuts
@Germanbiscuts 12 жыл бұрын
Finally, something on the KZbin that won't turn my brain to mush.... thanks Hank... and Scishow...
@MogofWar
@MogofWar 12 жыл бұрын
If you have a test on it in July, and you haven't read it by then, you fail at life... It would still be awesome of John did an episode on it.
@Soso19SMS
@Soso19SMS 11 жыл бұрын
I really like this video. I have a biology test tomorrow and it helped me big time. I even shared it with my friends :)
@ragnkja
@ragnkja 12 жыл бұрын
Henry Reich has an MSci in physics, and MP was started as a result of him tutoring physics. MinutePhysics and Sixty Symbols complement each other quite well in my opinion. I would also recommend DeepSkyVideos, about astronomy. A couple of the presenters there are also known from SS.
@CamilaAcuarelas
@CamilaAcuarelas 7 жыл бұрын
This helps so much with my Landscape Architecture Studio project!!!! THANKS!
@fangirl2643
@fangirl2643 12 жыл бұрын
I may not be Hank, but I am an ecology student. The succession of the area would most be dependent on the seed source and the soil. 1000 years after the event, soils would be thin, mostly, leading any tree species to be pine and, even more likely, aspens, which are the very first tree species to move in. However, there would most likely still be places of forbes, especially where the glacier took away soil. Looking into the glacial retreat in the American Midwest might help : )
@TheJaredtheJaredlong
@TheJaredtheJaredlong 12 жыл бұрын
In the field of Game Theory, the term used for random/unpredictable variables is: "Nature"
@bigdog31622
@bigdog31622 12 жыл бұрын
I think Thought Bubble would totally zazz up the production values of Hank's videos
@Ozycaevias
@Ozycaevias 12 жыл бұрын
I watch for the intro, I stay for the awesome. (Oh...and the learning... But that's just a side effect of staying.)
@ailidhmackichan716
@ailidhmackichan716 12 жыл бұрын
"You should come visit it some time" Hank, I wish I could
@smnk3
@smnk3 11 жыл бұрын
Brilliant. Exam this Friday.
@HM-rc7nn
@HM-rc7nn 8 жыл бұрын
You made ecology much easier for me.Thanks for your help 😊 Keep it up
@paulex12
@paulex12 12 жыл бұрын
3:19 Lycophytes (which are the coolest) are not seed plants, they have wind dispersed spores just like bryophytes and ferns. (Which is why they're often called fern allies.)
@sheepblitzer
@sheepblitzer 10 жыл бұрын
Plowing a field or tilling a garden is another example of a disturbance, and what we call "weeds" are the primary succession, nature's way of healing desolate land.
@phoenix-king779
@phoenix-king779 6 жыл бұрын
HEY U. 🔴🔴🔴🔴🔴 YOUR GOING TO DO GOOD ON YOUR FINALS.🔴🔴
@acmund
@acmund 12 жыл бұрын
Im an organic gardener...this is a fantastic video!
@ltericdavis2237
@ltericdavis2237 12 жыл бұрын
I know it's a constant, but please don't change, Hank! Crash Course Forever!
@Zulligula
@Zulligula 12 жыл бұрын
Profound implications for life and forests everywhere
@PURITYKIN
@PURITYKIN 12 жыл бұрын
Whenever I'm watching these video's and I learn a new word, I like to pretend I knew it before now.
@emeseszorenyi5245
@emeseszorenyi5245 4 жыл бұрын
Your graphics (by your team) are freakin awesome!!!
@ellyhall8394
@ellyhall8394 12 жыл бұрын
Hank, this video would've helped so much more 3 weeks ago when I had a test on exactly this in AP Environmental Science. -sigh-
@dolmalhamu6000
@dolmalhamu6000 11 жыл бұрын
thanku hank et al for the crash course.boosted my confidence. thanks again....
@SuperPrettyCOLORS
@SuperPrettyCOLORS 12 жыл бұрын
Crash Course AP Chemistry... I don't want to fail next year and you could make it interesting!
@WisemanSam599
@WisemanSam599 12 жыл бұрын
The presence of the forces is constant, even if the forces themselves change. Which works out well, because change is constantly changing. Death is also pretty constant, (but I supposed death counts as a change).
@brianaprado6205
@brianaprado6205 8 жыл бұрын
How poetic Hank!
@kibler2245
@kibler2245 2 жыл бұрын
What are answers for station 5
@sfobrien5225
@sfobrien5225 12 жыл бұрын
On the note of invasive species, we are introducing species at 1.a faster rate than ever seen before and 2. are moving those species a greater distance than seen before. Causing impressive extinction rates and loss of biodiversity, which again is bad for everybody
@TDawggggg
@TDawggggg 9 жыл бұрын
This guy looks like a combination of Bill Nye and Ben Folds.
@NoiretteBlanc
@NoiretteBlanc 11 жыл бұрын
Finally a crashcourse vid that helps me in my biology major!
@elllee653
@elllee653 11 жыл бұрын
I absolutely hate how he can't stay on topic.. i feel like he gives me a lot of info that doesn't really explain what the main topic is
@ceressculd
@ceressculd 6 жыл бұрын
"Who knows! Stuff happens!!"
@alibrastar28
@alibrastar28 10 жыл бұрын
Is that a little speeded up video or he talks that fast?
@TheBlaze4000
@TheBlaze4000 10 жыл бұрын
well wow hthat was fast woah shut the fuck up
@preternatural3231
@preternatural3231 6 жыл бұрын
this is the funniest comment i've ever read
@Jgosse
@Jgosse 12 жыл бұрын
This would of been awesome last week before my Eco final.
@HaileISela
@HaileISela 7 жыл бұрын
and the current industrial kind of "agriculture" is keeping a monoculture as stable as it can. it's insane. you should do an episode on permaculture and teach everyone about that, too. let's heal the planet and us in the process!
@markjustice5416
@markjustice5416 7 жыл бұрын
Crash Course is the best
@osas007oxygen4
@osas007oxygen4 5 жыл бұрын
Thank for this video i know it now
@TheLove2surf
@TheLove2surf 8 жыл бұрын
Many thanks! Excellent resource!!!
Ecosystem Ecology: Links in the Chain - Crash Course Ecology #7
10:10
CrashCourse
Рет қаралды 1,5 МЛН
Homochirality: Why Nature Never Makes Mirror Molecules
18:32
Steve Mould
Рет қаралды 1,6 МЛН
Ozoda - Alamlar (Official Video 2023)
6:22
Ozoda Official
Рет қаралды 10 МЛН
Andro, ELMAN, TONI, MONA - Зари (Official Audio)
2:53
RAAVA MUSIC
Рет қаралды 8 МЛН
ВЛОГ ДИАНА В ТУРЦИИ
1:31:22
Lady Diana VLOG
Рет қаралды 1,2 МЛН
OCCUPIED #shortssprintbrasil
0:37
Natan por Aí
Рет қаралды 131 МЛН
Lecture #9: How to Read so that you *Retain* Information
23:20
Jeffrey Kaplan
Рет қаралды 2,6 МЛН
Ecological Succession | Primary & Secondary
9:20
MAD GARDEN Science
Рет қаралды 5 М.
I attended Trump’s inauguration yesterday. Here are my thoughts.
7:01
Senator Bernie Sanders
Рет қаралды 4 МЛН
Death and Afterlife Across Religions: Crash Course Religions #17
12:32
Ecology - Rules for Living on Earth: Crash Course Biology #40
10:26
CrashCourse
Рет қаралды 1,8 МЛН
The Bayesian Trap
10:37
Veritasium
Рет қаралды 4,2 МЛН
I Misunderstood the Greenhouse Effect. Here's How It Works.
19:07
Sabine Hossenfelder
Рет қаралды 921 М.
Is Dust Mostly Dead Skin?
15:13
Veritasium
Рет қаралды 4,5 МЛН
Ozoda - Alamlar (Official Video 2023)
6:22
Ozoda Official
Рет қаралды 10 МЛН