IB Biology: Ecosystems, Adaptation, Population Dynamics, and Climate Change

Comprehensive practice flashcards matching IB Biology SL/HL specifications for B4.1, C4.1, D4.2, and D4.3.

How is a habitat defined in ecology?

A habitat is the natural home or environment of an organism, population, species, or community that provides all necessary resources for survival and reproduction.

What structural adaptations allow marram grass to reduce transpiration on sand dunes?

Leaves roll into a tube with stomata in sunken pits surrounded by fine hairs to trap moist air, covered by a thick waxy cuticle and supported by tough sclerenchyma tissue.

What physiological and root adaptations exist in the red mangrove (Rhizophora mangle)?

It possesses stilt roots for stability in mud, aerial roots (pneumatophores) for gas exchange at low tide, suberin-coated root epidermis to exclude salt, and accumulates mannitol and mineral ions to increase osmotic potential for water absorption.

What are the three main zones described by Shelford's Law of Tolerance?

The optimum range (maximum survival rate), zones of stress (reduced survival rates), and the zone of intolerance (where organisms cannot survive).

What abiotic conditions are required for coral reef formation?

Clear water for light penetration, water depth around $50\,m$, temperatures between $23^\circ\text{C}$ and $29^\circ\text{C}$, pH above $7.8$, and salinity levels between $32$ and $42\,ppt$.

Which two climatic variables determine terrestrial biome distribution on Whittaker's Climograph?

Mean annual temperature and mean annual precipitation.

How do cacti in the Americas and euphorbia in Africa illustrate convergent evolution?

Although geographically isolated and not closely related, both plant groups independently evolved similar structures, such as succulence and reduced leaves, to adapt to hot desert conditions.

What structural adaptations allow the saguaro cactus to survive in hot deserts?

Thick waxy cuticles to prevent water loss, spines (modified leaves) to reduce transpiration surface area and deter predators, internal water storage tissue, and a widespread root system.

How are camels adapted to conserve water and survive high desert temperatures?

They produce concentrated urine, extract water from faeces, store fat in humps for metabolic water/energy, possess long legs to stay above hot sand, reabsorb moisture in long nasal passages, and tolerate elevated body temperatures.

What adaptations characterize the red meranti tree (Shorea leprosula) in tropical rainforests?

It grows tall with a fast growth rate to reach the canopy light, forms large overground buttress roots for stability in shallow soil, produces broad dense leaves for light absorption, yields abundant fruit for animal dispersal, and contains leaf toxins for chemical defense.

What mechanism maintains distinct populations of the same species?

Reproductive isolation, such as geographic barriers, which prevents interbreeding between different groups.

What is sampling error in ecological studies?

The difference between the estimated population size obtained through sampling and the true size of the entire population.

What is the formula for the Lincoln index used in capture-mark-release-recapture?

$\text{Population Size} = \frac{M \times N}{R}$, where $M$ is the initial number marked, $N$ is the total recaptured, and $R$ is the number of marked individuals recaptured.

What key assumptions are made when using the Lincoln index to estimate population size?

No migration occurs, no births or deaths take place, marked individuals mix randomly back into the population with equal capture probability, and marks remain visible without harming survival.

What equation calculates a net change in population size?

$\text{Change in Population Size} = (N + I) - (M + E)$, where $N$ is natality, $I$ is immigration, $M$ is mortality, and $E$ is emigration.

What are the three main phases of a sigmoid population growth curve?

The exponential phase (rapid growth where natality greatly exceeds mortality), the transitional phase (growth slows as resources become limiting), and the plateau phase (population stabilizes around carrying capacity $K$).

What are two examples of intraspecific competition and two examples of intraspecific cooperation?

Competition: American robins defending nesting territory and male elephant seals fighting for mates. Cooperation: wolf pack hunting and honeybee waggle-dance foraging.

What mutualistic relationships occur in Fabaceae, Orchidaceae, and hard corals?

Fabaceae host nitrogen-fixing bacteria in root nodules; Orchidaceae pair with mycorrhizal fungi to enhance mineral absorption; hard coral polyps host photosynthetic zooxanthellae algae for nutrient exchange.

Why have invasive grey squirrels outcompeted endemic red squirrels in the UK?

Grey squirrels are larger and stronger, reproduce faster, outcompete red squirrels for food/habitat, and carry the squirrelpox virus to which grey squirrels are immune but red squirrels are vulnerable.

How do Canadian lynx and snowshoe hare populations demonstrate density-dependent regulation?

As hare populations rise, lynx food increases and lynx numbers grow; high lynx predation then reduces hare numbers, leading to a decline in lynx due to starvation, allowing the hare population to recover in a repeating cycle.

How do top-down and bottom-up controls regulate communities?

Top-down control uses top predators (e.g., Yellowstone wolves) to regulate prey and lower trophic levels; bottom-up control relies on resource availability to producers (e.g., nutrient levels controlling algal blooms).

How do black walnut trees and Penicillium fungi reduce competition?

Black walnut trees exhibit allelopathy by releasing juglone to inhibit competitor growth; Penicillium fungi secrete the antibiotic penicillin to suppress neighboring bacterial growth.

In a Chi-squared (\chi^2) test of association between two species, what is the critical value at p = 0.05 for df = 1?

The critical value is $3.841$; if calculated $\chi^2 > 3.841$, the null hypothesis is rejected, indicating a significant association between species.

What are the four essential requirements for long-term stability in natural ecosystems?

A continuous supply of energy, recycling of nutrients, genetic diversity, and climatic variables remaining within tolerance levels.

Why is the deforestation of the Amazon rainforest considered a potential climate tipping point?

Deforestation reduces transpiration and atmospheric water vapour, disrupting rainfall and wind patterns while transforming a crucial global carbon sink into a carbon emitter.

If the Brazilian Amazon forest area decreased from 4.1 million km^2 in 1970 to 3.4 million km^2 in 2000, what was the percentage change?

$\text{Percentage Change} = \frac{3.4 - 4.1}{4.1} \times 100 = -17.07\%$ (a $17.07\%$ reduction).

What defines a mesocosm and why are sealed glass vessels preferred?

A mesocosm is an experimental system examining natural environments under controlled conditions; sealed glass vessels allow energy transfer while preventing matter from entering or exiting.

What defines a keystone species?

A species that has a disproportionately large effect on the structure and biodiversity of its ecological community relative to its abundance.

What is maximum sustainable yield (MSY)?

The largest catch or harvest of a renewable biological resource that can be sustained over time without causing the population stock to decline.

How does fertilizer leaching lead to high Biochemical Oxygen Demand (BOD) during eutrophication?

Leached nitrates/phosphates trigger algal blooms that block light, killing sub-surface plants; aerobic bacteria decompose the dead biomass, consuming dissolved oxygen and causing BOD to spike above $8\text{--}10\,mg/L$.

What toxic effects result from the biomagnification of DDT and methylmercury?

DDT accumulates in apex predators like ospreys causing eggshell thinning and reproductive failure; methylmercury biomagnifies up marine food chains, causing neurological Minamata disease in humans consuming top predators.

How are macroplastics and microplastics categorized by size, and what impact do they have on sea turtles?

Macroplastics are debris larger than $25\,mm$; microplastics are smaller than $5\,mm$. Turtles ingest plastic bags mistaking them for jellyfish, causing intestinal blockages, starvation, or entanglement.

How was native vegetation restored at the Hinewai Reserve in New Zealand?

By stopping livestock grazing and using minimal interference management, allowing non-native gorse scrub to shelter emerging native seedlings that eventually overtopped and shaded out the light-intolerant gorse.

How do primary and secondary ecological succession differ?

Primary succession starts on bare, uncolonized land with no soil (e.g., after glacier retreat or volcanic eruption); secondary succession begins after a disturbance disrupts an existing ecosystem where soil remains intact.

What sequence of plant communities occurred during primary succession at Glacier Bay National Park?

Pioneer species (lichens/mosses) colonized bare rock, followed by alder thickets after $60\,$ years, which enriched soil nitrogen and were eventually succeeded by a spruce and hemlock climax forest.

What general trends occur in primary producers and ecosystems during primary succession?

Increases in overall plant size, primary production biomass, species diversity, food web complexity, and soil nutrient cycling capacity.

What mechanism enables lodgepole pines to persist in ecosystems with cyclical succession driven by wildfires?

They produce serotinous pine cones sealed with resin that open and release seeds only when exposed to the extreme heat of a forest fire.

What human actions result in arrested succession?

Livestock grazing (which eats growing seedlings and holds vegetation at a grassland state) and wetland drainage (which lowers the water table and restricts succession of wetland species).

Which two major greenhouse gases are driven up by human activities to cause anthropogenic climate change?

Carbon dioxide ($CO_2$ from fossil fuel/wood burning) and methane ($CH_4$ from ruminant livestock and rice farming).

What two positive feedback loops accelerate global warming in the Arctic?

1. Melting white ice exposes darker land/water, increasing solar radiation absorption and further heating. 2. Thawing permafrost allows bacterial decomposition of peat, releasing $CO_2$ and $CH_4$ to drive additional warming.

Why are boreal forests (taiga) shifting from carbon sinks to net carbon sources?

Warmer temperatures and reduced winter snow cause severe droughts and forest browning, decreasing primary productivity while triggering high-intensity wildfires that combust plant biomass and soil peat.

How does polar ice loss threaten emperor penguins (Aptenodytes forsteri) and walruses?

Early breakout of landfast sea ice destroys emperor penguin breeding colonies before chicks can swim; loss of sea ice floes forces walruses onto overcrowded land beaches, increasing young mortality from stampedes.

Why does warming ocean surface water disrupt nutrient upwelling and marine food chains?

Warm surface water creates a low-density surface layer that suppresses the rising of cold, nutrient-rich deep water, limiting nitrate and phosphate availability for phytoplankton primary production.

What are two specific examples of climate-induced species range shifts?

Upslope range shifts in tropical montane birds in New Guinea (causing habitat compression) and poleward range shifts in North American tree species like sugar maples moving northward.

What chemical reaction causes ocean acidification, and how has ocean pH changed since the 19th century?

Dissolved $CO_2$ reacts with water to form carbonic acid ($H_2CO_3$), releasing $H^+$ ions that consume carbonate ions ($CO_3^{2-}$) required for coral skeleton calcification; mean ocean pH dropped from $8.179$ to $8.069$.

What causes coral bleaching and why is it dangerous to coral survival?

Elevated sea temperatures stress corals, causing them to expel their mutualistic photosynthetic zooxanthellae algae; bleached corals lose their color and primary food source, leading to starvation if warm conditions persist.

How does Sphagnum moss promote long-term soil carbon sequestration in wetlands?

It releases $H^+$ ions to create an acidic environment, which inhibits decomposer microbes in anaerobic waterlogged soil and prevents plant organic matter from breaking down.

What is phenology and what cues trigger phenological events?

Phenology is the study of the timing of cyclic biological events (e.g., budburst, migration, flowering); these events are cued by abiotic factors such as temperature patterns or photoperiods (day length).

How does global warming disrupt the phenological synchrony between great tits (Parus major) and forest caterpillars?

Warming temperatures cause forest caterpillar biomass to peak 2 weeks earlier, while great tit egg hatching advances by only 1 week, creating a temporal mismatch between chick food demand and prey availability.

How has climate change altered the life cycle of the spruce bark beetle (Ips typographus)?

Warmer summer temperatures have accelerated beetle development, shortening their life cycle from 2 years down to 1 year, causing population explosions that destroy spruce forests.

How has climate change driven natural selection and evolutionary change in Finnish tawny owl (Strix aluco) populations?

Reduced snow cover gives brown-plumaged owls a camouflage advantage over grey variants during milder winters; brown owls survive and reproduce more successfully, increasing the frequency of the brown plumage allele.