A4.2 Conservation of biodiversity

The question asks why a single survey is insufficient to conclude that no biodiversity crisis is occurring. The key concept being tested is the need for repeated measurements over time to identify trends.

A biodiversity crisis is characterised by a declining trend in species richness or population sizes. A single data point — 120 species recorded at one time — tells us nothing about whether that number was previously 200 or has always been 120.

Only by comparing data from multiple surveys at different time points can a researcher determine whether species richness is stable, increasing, or declining. Without a baseline or historical comparison, the observation of 120 species is meaningless in terms of identifying a crisis.

The correct answer is: 'A single measurement cannot reveal whether species diversity is increasing, declining, or stable over time.' This directly addresses the logical flaw — trends require multiple data points.

The question tests understanding of why longitudinal (repeated over time) biodiversity monitoring is necessary to detect a biodiversity crisis, rather than relying on a snapshot survey.

While observer bias and weather are real concerns in fieldwork, this answer addresses sampling accuracy, not the fundamental inability to detect trends. It is a secondary methodological issue, not the core flaw in the biologist's reasoning.

This statement is not generally true — birds are widely used as biodiversity indicators. More importantly, it does not address why a single survey is insufficient regardless of the taxon surveyed.

Accounting for seasonal variation improves the accuracy of a single year's survey, but this still does not allow detection of long-term trends. This answer conflates within-year variation with between-year trend analysis.

The remaining option — 'A single measurement cannot reveal whether species diversity is increasing, declining, or stable over time' — is correct. Detecting a crisis requires comparison across multiple time points to identify a directional trend.

This question tests knowledge of biodiversity hotspots — regions with disproportionately high species richness relative to their geographic area. Tropical rainforests are the most prominent example.

Tropical rainforests cover roughly 6% of Earth's land surface but are estimated to contain approximately 50% of all species. They also support exceptionally high endemism — many species found there occur nowhere else on Earth.

The combination of high species richness, high endemism, and ongoing habitat destruction means that loss of tropical rainforest results in a disproportionately large number of species extinctions compared to losing equivalent areas of lower-diversity habitat.

The correct answer is: 'They contain approximately 50% of all species on Earth and support high levels of endemism.' This directly reflects the biodiversity hotspot concept using accurate data from the notes.

The question tests knowledge of why tropical rainforests are prioritised for conservation — specifically their role as biodiversity hotspots with high species richness and endemism.

While tropical rainforests are indeed old, the claim that they have been 'undisturbed for millions of years' is factually incorrect — they face severe ongoing deforestation. Age alone does not explain their conservation priority status.

The 50% oxygen figure is a common misconception — most atmospheric oxygen production is attributed to marine phytoplankton. While rainforests do influence water cycling, this is not the primary biodiversity-based reason for their conservation priority.

This is factually wrong. Tropical rainforests are among the most heavily deforested ecosystems on Earth, with massive ongoing habitat destruction, particularly in the Amazon, Congo Basin, and Southeast Asia.

The correct answer is 'They contain approximately 50% of all species on Earth and support high levels of endemism.' This accurately reflects the biodiversity data and explains why conserving rainforests has an outsized impact on global species preservation.