Explain causes of biodiversity loss

5.3.1 · Biology › Conservation & Human Impact

Overview

Biodiversity loss Earth par life ki variety aur variability mein decline hai, jo genetic, species, aur ecosystem levels par measure hoti hai. Causes ko samajhna effective conservation strategies develop karne ke liye critical hai.

[!intuition] Biodiversity Decline Kyun Hoti Hai?

Biodiversity ek dynamic equilibrium mein exist karti hai: speciation nayi diversity create karta hai jabki extinction use remove karta hai. Human activities ne extinction rates ko natural background rates se 100-1000× upar accelerate kar diya hai (~1 species/million/year). Biodiversity ko ek bank account ki tarah socho—hum massive withdrawals (extinctions) kar rahe hain jabki deposits (nayi species evolve hone ke liye habitat) block kar rahe hain.

Mechanisms koi mystery nahi hain: har species ko space, resources, aur stable conditions chahiye. Human expansion in requirements ko systematically evolution ki adapt karne ki speed se kahin zyada tezi se remove karta hai.

[!definition] The Big Five: HIPO Framework

Ecologists HIPPO ko paanch primary drivers ke liye ek mnemonic ke roop mein use karte hain:

1. Habitat Loss & Fragmentation
2. Invasive Species
3. Pollution
4. Population Growth (human)
5. Overexploitation

Ye drivers aksar synergize karte hain—habitat fragmentation populations ko pollution ke liye vulnerable banata hai, invasive species disturbed habitats mein zyada aasani se colonize kar leti hain, etc.

Detailed Mechanisms

1. Habitat Loss & Fragmentation

Kya hota hai: Natural ecosystems ko human use (agriculture, cities, infrastructure) ke liye convert kiya jaata hai. Bacha hua habitat isolated patches mein toot jaata hai.

Extinction kyun hoti hai:

• Area effect: Chhota habitat → kam resources → chhoti populations → stochastic events se zyada extinction risk
• Edge effects: Fragments mein interior ke relative zyada "edge" hoti hai; edges mein altered microclimates, predation, invasive species penetration hoti hai
• Isolation: Populations ke beech gene flow ruk jaata hai → inbreeding → genetic diversity ka loss → reduced adaptive potential

Iske peeche ka math: Species-area relationship ise quantify karta hai:

$S=c{A}^z$

Jahaan:

• $S$ = number of species
• $A$ = habitat area
• $c$ = constant (region par depend karta hai)
• $z$ = species-area exponent (typically 0.15-0.35)

Derivation: Ye power law kyun?

Is observation se shuru karo ki bade areas mein zyada habitat types hote hain aur badi populations support ho sakti hain. Agar hum assume karein:

1. Har unit area mein kisi given species ke hone ki probability $p$ hai
2. Species distributions clustered hain (random nahi)
3. Bade areas regional species pool se zyada sample karte hain

Tab statistical sampling theory aur empirical observation ke through, hum paate hain ki species area ke power function ke roop mein accumulate hoti hain, linearly nahi. Exponent $z$ ye reflect karta hai ki species kaise distribute hain—zyada $z$ ka matlab hai species zyada locally concentrated hain.

Practical consequence: Agar tum 90% habitat lose kar do ($A\to 0.1A$):

$S_{new}=c(0.1A{)}^{0.25}=0.1^{0.25}\cdot S_{original}\approx 0.56\cdot S_{original}$

Tum ~44% species lose kar dete ho even though 10% habitat bacha rehta hai!

[!example] Worked Example 1: Forest Fragmentation

Scenario: Ek 10,000 km² rainforest mein initially 500 species hain (measured). Logging ise 1,000 km² scattered fragments tak reduce kar deta hai. $z=0.25$ is region ke liye.

Step 1: Species-area relationship apply karo

• $S_1=c(10000{)}^{0.25}$
• $S_2=c(1000{)}^{0.25}$

Step 2: $c$ eliminate karne ke liye ratio lo: $\frac{S_2}{S_1}={\left(\frac{1000}{10000}\right)}^{0.25}=(0.1{)}^{0.25}=0.562$

Ye step kyun? Constant $c$ unknown hai lekin jab hum same region ke do states compare karte hain to cancel ho jaata hai.

Step 3: Nayi species richness calculate karo: $S_2=0.562\times 500=281\text{ species}$

Result: ~219 species extinctions (44% loss) expect karo 90% habitat loss se.

Ye dikhe se bura kyun hai: Ye sirf immediate "extinction debt" hai—minimum viable size se neeche ki populations decades mein extinct ho jaayengi even agar aur koi habitat loss na ho.

2. Invasive Species

Kya hota hai: Non-native species nayi ecosystems mein introduce hoti hain jahaan unke natural predators/competitors nahi hote.

Extinction kyun hoti hai:

• Competition: Invasives resources ke liye natives ko outcompete karti hain (often generalists specialists ko beat karte hain)
• Predation: Naive prey mein evolved defenses nahi hote (e.g., rats flightless island birds khaate hain)
• Disease: Invasives novel pathogens laati hain (e.g., chytrid fungus globally amphibians ko maar raha hai)
• Ecosystem engineering: Kuch invasives fundamental habitat structure alter kar deti hain (e.g., kudzu forests ko smothering karta hai)

The mechanism: Competitive exclusion principle—identical niches wali do species coexist nahi kar saktiyn. Thodi si bhi advantage wali species doosri ko extinct kar deti hai.

Ecology se derivation: Do species ko same resource ke liye compete karte consider karo. Population growth follow karta hai:

$\frac{d{N}_1}{dt}=r_1{N}_1\left(1-\frac{N_1+\alpha N_2}{K_1}\right)$

$\frac{d{N}_2}{dt}=r_2{N}_2\left(1-\frac{N_2+\beta N_1}{K_2}\right)$

Jahaan $\alpha$ = species 2 ka species 1 ki carrying capacity par effect, $\beta$ = reverse effect.

Equilibrium par ($dN/dt=0$), agar invasive species 2 ka zyada $r$ ya $K$ hai, to ye $N_1\to 0$ drive kar deta hai.

[!example] Worked Example 2: Brown Tree Snake in Guam

Background: Snake ~1950 mein introduce hua; Guam mein koi native snakes nahi the, isliye birds ne koi defenses evolve nahi ki thi.

Ye kyun kaam kiya:

1. Prey naivety: Birds ground/low branches par nest karte the (historically koi snake predators nahi the)
2. No predators: Snake ke Guam par koi natural enemies nahi the
3. High reproduction: Ek female 4-12 offspring/year produce karti hai
4. Generalist diet: Birds, lizards, bats khaata tha—jo bhi available ho

Result: 1980s tak 12 mein se 10 native forest bird species extinct ho gayi. Do survivors (Mariana crow, Micronesian kingfisher) sirf captivity mein exist karte hain.

Lesson: Island ecosystems khaas taur par vulnerable hote hain—species jo isolation mein evolve hui hain unme defenses nahi hote.

3. Pollution

Kya hota hai: Contaminants (chemical, noise, light, plastic) ka introduction jo environmental conditions alter kar dete hain.

Extinction kyun hoti hai:

• Direct toxicity: Poisons organisms ko maarte hain (e.g., pesticides, heavy metals)
• Endocrine disruption: Chemicals hormones ki tarah mimic karte hain, reproduction disrupt karte hain (e.g., atrazine frogs ko feminize karta hai)
• Bioaccumulation: Toxins food chains mein concentrate hote hain (e.g., DDT → raptors mein eggshell thinning)
• Habitat degradation: Eutrophication → algal blooms → oxygen depletion → dead zones

Bioaccumulation ka mechanism:

Ek aisi toxin se shuru karo jo:

1. Fat-soluble (lipophilic) ho
2. Persistent ho (break down nahi hoti)
3. Aasani se excrete nahi hoti

Har trophic level apne biomass se ~10× zyada prey consume karta hai (10% energy transfer efficiency ki wajah se). Agar toxin excrete nahi hoti:

${\text{Concentration}}_{leveln}={\text{Concentration}}_{leveln-1}\times \text{Consumption ratio}\times \text{Retention}$

Ek predator ke liye jo 10 kg prey/kg body weight khaata hai aur 100% retention hai, concentration har trophic transfer par 10× multiply hoti hai. Neeche diya worked example mein paanch transfers hain (water → phytoplankton → zooplankton → small fish → large fish → falcon), jo total magnification deta hai:

$C_{\text{top}}=C_{\text{base}}\times 10^5=100,000\times C_{\text{base}}$

(Generally, $n$ transfers se $10^n$ ka factor milta hai; chaar-step ki chhoti chain se $10^4$ milega, etc.)

[!example] Worked Example 3: DDT in Peregrine Falcons

Scenario: DDT 1 ppm par water mein enter karta hai → five trophic transfers ke through food chain mein accumulate hota hai.

Trophic levels:

1. Water: 1 ppm DDT
2. Phytoplankton: DDT absorb karte hain, 10 ppm (10× concentration factor)
3. Zooplankton: phytoplankton khaate hain, 100 ppm (10× per level)
4. Small fish: 1,000 ppm
5. Large fish: 10,000 ppm
6. Falcon: 100,000 ppm (= 100,000 mg/kg ≈ body fat ka 10% by mass)

Effect: DDT metabolite DDE (dichlorodiphenyldichloroethylene) calcium metabolism mein interfere karta hai → thin eggshells → incubation ke dauran eggs toot jaate hain → reproductive failure → population crash (1970s tak US mein 93% decline).

Ye step kyun? Har trophic level ko thermodynamic inefficiency ki wajah se time ke saath apne body weight se ~10× zyada prey consume karna padta hai (2nd law—heat loss). Kyunki DDT metabolize/excrete nahi hoti, ye har step par accumulate hoti hai, isliye paanch transfers concentration ko $10^5$ se multiply kar dete hain.

Recovery: DDT 1972 mein ban hua → populations recover ho gayi (lekin dheere—DDT decades tak soil mein persist karti hai).

4. Population Growth (Human)

Kya hota hai: Human population 8 billion (2022) tak pahunch gayi, consumption patterns ke saath jo annually ~1.7 Earths worth of resources require karti hain.

Extinction kyun hoti hai:

• Resource demand: Zyada humans → zyada land, water, energy chahiye → habitat conversion
• Per-capita impact: Sirf numbers nahi—developed nations developing nations se 32× zyada resources consume karte hain
• Infrastructure: Roads, cities, dams agriculture ke bina bhi habitat fragment karte hain

The multiplier effect: ==I = P × A × T== (IPAT equation)

$\text{Impact}=\text{Population}\times \text{Affluence}\times \text{Technology}$

Jahaan:

• $P$ = population size
• $A$ = consumption per person (GDP/capita as proxy)
• $T$ = environmental impact per unit consumption (efficiency)

Ye formulation kyun? Har factor doosron ko multiply karta hai:

• 2× population same consumption ke saath = 2× impact
• Same population 2× per person consume kare = 2× impact
• Same population & consumption lekin 0.5× efficiency = 0.5× impact

Resource accounting se derivation: Total resource use $R$ hai:

$R=(\text{people})\times \left(\frac{\text{consumption}}{\text{person}}\right)\times \left(\frac{\text{resources}}{\text{consumption unit}}\right)$

Ye $R=P\times A\times T$ mein simplify ho jaata hai.

[!example] Worked Example 4: Agricultural Expansion

Scenario: Region ko 1 million aur logon ko feed karna hai. Har person ko 200 kg grain/year chahiye. Current yield 4 tons/hectare hai.

Step 1: Total grain needed calculate karo: $1,000,000\text{ people}\times 200\text{ kg/person}=200,000,000\text{ kg}=200,000\text{ tons}$

Ye step kyun? Agricultural productivity se compare karne ke liye total demand mein convert karo.

Step 2: Land required calculate karo: $\frac{200,000\text{ tons}}{4\text{ tons/hectare}}=50,000\text{ hectares}=500{\text{ km}}^2$

Result: 500 km² natural habitat ko farmland mein convert karna padega. Agar ye $z=0.25$ wala forest tha aur original 5000 km² mein 200 species thin:

$S_{\text{lost}}=200\times \left[1-{\left(\frac{4500}{5000}\right)}^{0.25}\right]\approx 200\times 0.025=5\text{ species}$

Compounding factor: Population growth exponentially continue karti hai → deforestation accelerate hoti hai.

5. Overexploitation

Kya hota hai: Species ko unki reproduction rate se tezi se harvest karna.

Extinction kyun hoti hai:

• Sustainable yield exceed karna: Harvest rate > reproduction rate → population decline
• Allee effects: Kam densities par, reproduction fail ho jaati hai (mates nahi mil paate, cooperative breeding fail ho jaata hai)
• Economic incentive: Rarity value badhati hai (e.g., rhino horn), jo aakhri individuals ko hunt karne ka perverse incentive create karta hai

Sustainable harvest ka math:

Logistic growth se shuru karo:

$\frac{dN}{dt}=rN\left(1-\frac{N}{K}\right)$

Ye net population growth represent karta hai—births minus natural deaths.

Maximum sustainable yield (MSY) wahaan hota hai jahaan growth rate sabse zyada hoti hai. Derivative lo:

$\frac{d}{dN}\left[rN\left(1-\frac{N}{K}\right)\right]=r\left(1-\frac{2N}{K}\right)=0$

Ye step kyun? Hum optimal harvest determine karne ke liye growth rate function ka maximum find kar rahe hain.

$N_{\text{MSY}}=\frac{K}{2}$

Is population par, growth rate hai:

${\frac{dN}{dt}|}_{N=K/2}=r\frac{K}{2}\left(1-\frac{1}{2}\right)=\frac{rK}{4}$

Critical insight: $rK/4$ se zyada harvest karo aur population extinction ki taraf spiral karti hai. Exactly itna harvest karo to sirf tab kaam karta hai jab population $K/2$ par ho—lekin agar population $K/2$ se neeche gir jaaye, to MSY harvest extinction drive kar deti hai.

[!example] Worked Example 5: Cod Fishery Collapse

Scenario: Cod population $K=1,000,000$ tons, $r=0.3$/year. Fishery MSY par harvest karta hai.

Step 1: MSY calculate karo: $\text{MSY}=\frac{rK}{4}=\frac{0.3\times 1,000,000}{4}=75,000\text{ tons/year}$

Step 2: Kya hoga agar initial population $K$ ka 60% ho? $N_0=0.6K=600,000\text{ tons}$

Us saal growth: $\frac{dN}{dt}=0.3\times 600,000\times \left(1-\frac{600,000}{1,000,000}\right)=72,000\text{ tons}$

Lekin harvest = 75,000 tons, isliye: $N_1=600,000+72,000-75,000=597,000\text{ tons}$

Ye step kyun? Growth minus harvest agale saal ki population deta hai. Kyunki harvest > growth hai, population decline karti hai.

Year 2: $dN/dt=0.3\times 597,000\times 0.403=72,100$ tons
Harvest abhi bhi 75,000 → $N_2=594,100$ tons

Result: Population downward spiral karti hai. Ye Grand Banks cod ke saath hua—overfishing se collapse ho gaya, 30+ saal baad bhi fishing moratorium ke bavajood recover nahi hua.

The Allee effect trap: $K$ ke ~30% se neeche, cod schools mates efficiently find karne ke liye bahut sparse ho jaate hain → effective $r$ drop ho jaata hai → collapse accelerate ho jaata hai.

[!mistake] Common Misunderstandings

Mistake 1: "Species extinct hoti hain kyunki wo unfit hain"

Kyun sahi lagta hai: Hum natural selection ke baare mein padhte hain—"survival of the fittest." Extinct species kam fit hogi, hai na?

The fix: Fitness is environment-specific hoti hai. Ek species jo apne environment mein perfectly adapted hai extinct ho sakti hai agar wo environment evolution ke adapt hone se tezi se destroy ho jaaye. Passenger pigeon incredibly successful tha (billions of individuals) jab tak humans ne unhe decades mein hunt karke extinct kar diya. Wo "unfit" nahi the—selection pressure (hunting) unki reproductive capacity se zyada thi. Evolution ko time aur genetic variation chahiye—rapid environmental change dono ko outpace kar deti hai.

Mistake 2: "Habitat fragments sirf chhote hain—same habitat, kam space"

Kyun sahi lagta hai: Agar tum ek forest ko aadha karo, to tumhare paas do aadhe-forests hain.

The fix: Fragments mein fundamentally alag properties hoti hain:

• Edge effects: Ek 1 km² square mein 4 km ki edge hai. Chaar 0.25 km² squares mein 8 km ki edge hai—same total area ke liye double edge exposure.
• Isolation: Gene flow ruk jaata hai. Populations inbred ho jaati hain. Ek fragment mein extinction ko doosre se recolonize nahi kiya ja sakta.
• Matrix hostility: Fragments ke beech ka area (farms, roads) lethal hai—movement prevent karta hai even agar fragments close bhi hon.

Is tarah socho: Aadha kiya hua ghar do aadhe-ghar nahi hote—walls ab exterior walls hain jo weather mein expose hain, heating/cooling costs double ho jaate hain, aur tum rooms ke beech move nahi kar sakte.

Mistake 3: "Pollution sirf polluted areas mein species ko affect karti hai"

Kyun sahi lagta hai: Agar ek river polluted hai, us river ki fish mar jaayegi, lekin doosri rivers ki fish theek hain.

The fix: Bioaccumulation aur long-range transport. DDT sprayed in the US Antarctic penguins mein mila. Mercury from coal plants oceans door tuna mein accumulate hoti hai. Microplastics ab Mariana Trench mein bhi mile hain. Persistent pollutants:

1. Volatilize hote hain ya water systems mein wash ho jaate hain
2. Currents/atmosphere ke through globally spread ho jaate hain
3. Food chains mein concentrate hote hain
4. Source se door apex predators mein appear karte hain

Mistake 4: "Invasive species sirf tabhi natives ko outcompete karti hain jab wo 'better' hon"

Kyun sahi lagta hai: Competition → best competitor jeetta hai.

The fix: Invasives often absolute sense mein "better" hone ki wajah se nahi, balki in wajahon se succeed karti hain:

• Enemy release: Home range se predators/parasites/diseases ko peeche chhod aate hain
• Naive prey/competitors: Natives mein evolved defenses nahi hote
• Disturbed habitats: Invasives often generalists hoti hain jo human-altered landscapes mein thrive karti hain jahaan specialists fail ho jaate hain

Native species undisturbed habitat mein "better" competitors ho sakti hain, lekin agar habitat already degraded hai, to invasives us disturbance ko exploit karti hain. Ye fair fight nahi hai—ye ek ambush hai.

[!recall]- Ek 12-Saal-Ke Bacche Ko Samjhao

Earth ko ek bahut badi library socho jisme millions of alag-alag books (species) hain. Har book unique hai aur likhne mein millions of years lage.

Ab socho humans ek construction company chala rahe hain. Humein buildings ke liye jagah chahiye, isliye hum library ke sections gira rahe hain banane ke liye:

• Habitat loss = bookshelves giraaना. Kam shelves → kam books fit hoti hain → kuch books ko jaana padta hai
• Fragmentation = shelves ke beech walls lagaana. Ek taraf ki books doosri taraf ki books se "baat" nahi kar sakti (koi genetic mixing nahi)

Lekin hum doosri libraries se nayi books bhi la rahe hain (invasive species) jo bade font mein likhi hain aur zyada shelf space leti hain, originals ko bahar dhakelte hue.

Aur hum shelves par coffee gira rahe hain (pollution)—kuch books daag ho jaati hain aur kharab ho jaati hain, khaaskar high shelves wali rare books par jo coffee drip hoti hai (bioaccumulation).

Plus, humari construction company badhti ja rahi hai (population growth), zyada aur zyada buildings chahiye, isliye hum shelves aur tezi se girate hain.

Finally, hum books check out kar rahe hain aur kabhi return nahi kar rahe (overexploitation)—unhe ghar le jaate hain padhne ke liye lekin itni saari le lete hain ki library khaali ho jaati hai pehle ki nayi copies print ho sakein (reproduction).

Problem sirf ek cheez nahi hai—ye sab saath mein ho raha hai, library ke nayi books print karne ki speed se kahin tezi se (evolution bahut slow hai). Ek baar book gayi, gayi hamesha ke liye. Yehi extinction hai.

[!mnemonic] HIPO Yaad Rakho

H - Homes destroyed (habitat loss)
I - Invaders arrive (invasive species)
P - Poisons spread (pollution)
P - People multiply (population growth)
O - Over-harvesting (overexploitation)

Visual: Ek sad HIPPO ki picture banao jiska ghar (habitat) aliens (invasives) ne invade kiya ho, paani poison hai (pollution), logon ki bheed hai (population), aur usse hunt kiya ja raha hai (overexploitation).

Connections

• Island Biogeography Theory – species-area relationship ko mathematically explain karta hai
• Ecological Succession – disturbed habitats invasive generalists ko favor karte hain
• Population Dynamics – logistic growth model, Allee effects, MSY
• Trophic Cascades – top predator loss poori ecosystems ko kaise affect karta hai
• Conservation Strategies – in drivers ke solutions (habitat corridors, captive breeding, etc.)
• Climate Change Effects on Biodiversity – emerging sixth driver (kabhi kabhi HIPO mein HIPPCO ke roop mein include hota hai)
• Genetic Drift vs Gene Flow – fragmentation genetic diversity kyun reduce karta hai
• Ecosystem Services – biodiversity loss prevent karne ke economic reasons

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