5.3.7
Intuition Ek saansh mein badi baatKisi organism ko aisi jagah move karo jahan uske koi natural predators nahi hain , koi competitors nahi hain jo uske liye adapt hue hon , aur bahut saari naive prey available hai , toh woh sankhya mein bahut tezi se badh sakta hai — poore ecosystem ko reshape karke. Invasive species basically ek "cheat code" organism hai jo ek aisi game mein drop kiya gaya hai jisme uske khilaf koi defence coded hi nahi hai.
Native species ::= woh species jo kisi region mein evolve hui ya naturally wahan pahunchi lambe samay ke saath.Introduced (alien / exotic) species ::= woh species jo humans dwara (deliberately ya accidentally) ek naye region mein move ki gayi.Invasive species ::= woh introduced species jo tezi se failti hai aur ecological ya economic nuksan karti hai .
⚠️ Har introduced species invasive nahi hoti. Zyaadatar introductions fail ho jaate hain ya harmless rehte hain. Ek species invasive tab hoti hai jab woh establish ho, failey, AUR damage bhi kare.
WHY distinction matter karti hai: conservation law aur paisa invasive species ko specifically target karta hai. Har foreign plant ko "invasive" kehna effort waste karta hai; harm criterion action ko focus karta hai.
Socho ki normally kya cheezein kisi population ko uski home range mein limit karti hain:
Predators usse khaate hain.Competitors uske resources le jaate hain.Parasites & diseases usse kamzor karti hain.
Yeh limits us species ke saath hazaaron saalon mein co-evolve hui hain. Jab tum species ko kahin aur move karte ho, tum woh limits peeche chhod dete ho . Yahi Enemy Release Hypothesis hai.
Intuition Population boom ki derivationEk population is tarah change hoti hai
d t d N = r N ( 1 − K N ) r K
Yeh equation kyun? Growth is baat ke proportional hoti hai ki kitne hain (r N 1 − N / K
Native range mein, predators/disease effectively r K
r K
Result: ghar se kaafi steep aur zyaada upar curve. Yahi invasion boom hai.
HOW fast? Unchecked growth ke saath (N ≪ K d t d N ≈ r N N ( t ) = N 0 e r t t 2 = r ln 2 r
Har route native biodiversity ko reduce karta hai, aur biodiversity loss headline conservation concern hai.
Worked example 1 — Brown tree snake on Guam (predation)Cargo ships ke zariye accidentally introduce kiya gaya (~1950s). Guam par koi predators nahi the; native birds zameen par nest banate the jinhe snakes ka koi darr nahi tha .
Woh kyun collapse hue: naive prey + koi snake predators nahi → snake r Result: 12 mein se 10 native forest bird species extinct ho gayi.Yeh step kyun (biodiversity link): birds khone se seed dispersers chale gaye → knock-on plant decline (ek trophic cascade ).
Worked example 3 — Cane toad in Australia (predation + poison)Sugarcane par beetles khaane ke liye introduce kiya gaya; lekin iske bajaye native predators ko zahar de diya.
Native predators kyun marte hain: woh toad khaate hain aur uski skin toxin unhe maar deti hai — unhone kabhi resistance evolve nahi ki.Result: quolls, snakes, goannas decline karte hain; toad unchecked failta rehta hai.
Worked example 4 — Grey squirrel vs red squirrel, UK (competition + disease)
Competition: grey squirrel wider diet khaata hai, fragmented woods mein better survive karta hai.Disease: grey squirrelpox carry karta hai, khud ke liye harmless lekin reds ke liye lethal.Disease kyun decisive hai: jahan bhi reds theek compete kar lete hain, pathogen (+
Common mistake "Saari non-native species harmful hoti hain."Kyun sahi lagta hai: hum "invasive" itna sunte hain ki lagta hai foreign = bura.
The fix: zyaadatar introductions fail ya benign hoti hain; wheat, tomatoes, honeybees non-native aur beneficial hain. Harm — origin nahi — invasive define karta hai.
Common mistake "Invasives zyaada powerful/'fitter' organisms hain."Kyun sahi lagta hai: woh itne dramatically jeette hain ki superiority jaisi lagti hai.
The fix: woh intrinsically superior nahi hain — woh jeette hain kyunki naye environment mein unke dushman nahi hain . Cane toad ko apne ghar wapas bhejo uske predators ke saath aur woh ordinary hai. Yeh context ke baare mein hai, raw strength nahi.
Common mistake "Ek species add karna hamesha biodiversity badhata hai."Kyun sahi lagta hai: +1 species = zyaada species, pakka?
The fix: ek invasive bahut saari native extinctions drive kar sakti hai (Guam: +1 snake, −10 birds). Net biodiversity girta hai.
Common mistake "Agar hum invasive ko remove kar dein, ecosystem turant recover ho jaata hai."Kyun sahi lagta hai: cause hata do → effect hata do.
The fix: extinctions permanent hain; altered soil/fire regimes persist karti hain. Recovery slow, partial, kabhi kabhi impossible hoti hai.
Recall Jawab padhne se pehle predict karoEk lake ko ek floating invasive plant milti hai jiska doubling time 2 hafte hai. Forecast karo ki 3 mahinon mein (a) surface ke neeche sunlight, (b) dissolved oxygen, (c) fish ke saath kya hoga. Phir Example 2 se compare karo.
Verify: sunlight ↓ (mats block karti hai) → submerged photosynthesis ↓ → O₂ ↓ → fish mar jaati hai. Exponential N 0 e r t r = ln 2/2 wk
What defines an invasive species (vs merely introduced)? Yeh humans dwara introduce ki gayi hai AUR tezi se failti hai AUR ecological/economic nuksan karti hai.
Enemy Release Hypothesis Introduced species thrive karti hain kyunki woh apne native predators, competitors, parasites aur diseases se bachh jaati hain.
Why do invasives often boom in population? Enemies ka loss intrinsic growth rate r aur carrying capacity K ko badhata hai, toh logistic curve zyaada steep aur zyaada upar jaati hai.
Name the 5 impact pathways of invasives Competition, predation, disease/parasite introduction, habitat alteration, hybridisation.
Guam brown tree snake — mechanism and result Naïve ground-nesting birds par predation jinme koi snake defence nahi tha → ~10 forest bird species ka extinction.
Water hyacinth — mechanism Dense floating mats sunlight block karte hain → submerged plants mar jaati hain → dissolved O₂ girta hai → fish mar jaati hai (habitat alteration).
Cane toad — why native predators die Woh toxic toad khaate hain aur unme uski skin poison ke khilaf koi evolved resistance nahi hai.
Grey vs red squirrel — two mechanisms Competition (broader diet) + disease (grey lethal squirrelpox carry karta hai).
Why is "non-native = harmful" wrong? Zyaadatar introductions harmless/beneficial hain (wheat, honeybees); sirf harmful ones invasive hain.
What is a trophic cascade in invasion context? Ek species ko hatana/add karna (e.g. bird seed-dispersers) food web mein knock-on changes trigger karta hai.
Doubling time formula for unchecked growth t₂ = ln2 / r.
Recall Feynman: ek 12-saal ke bachhe ko explain karoSocho ek video game jisme har monster ki ek weakness hoti hai jo heroes jaante hain kaise beat karein. Ab koi doosri game se ek bilkul naya monster drop karta hai — kisi ko uski weakness pata nahi, aur uske koi dushman nahi hain. Woh pagalon ki tarah multiply karta hai aur level barbad kar deta hai. Wahi naya monster ek invasive species hai. Baat yeh nahi ki woh sabse zyaada strong hai — baat yeh hai ki is jagah ke paas abhi tak usse fight karne ka koi tarika nahi hai.
Mnemonic 5 impacts yaad karo:"CP DHH" → C ompetition, P redation, D isease, H abitat change, H ybridisation. Kaho "Cops Patrol During Harsh Hours."
Logistic Growth & Carrying Capacity — boom ke peeche r/K ka mathsBiodiversity & its Importance — jo invasives kharab karti hainFood Webs & Trophic Cascades — ek loss baaki sab par kaise effect karta haiConservation Strategies — quarantine, biocontrol, eradicationNatural Selection & Coevolution — native prey mein defences kyun nahi hainHuman Impact on Ecosystems — introductions ek human-driven pressure ki tarah
establishes spreads causes harm
leaves predators competitors disease behind
logistic model dN/dt = rN 1-N/K
competition predation disease
habitat change hybridisation
