Ecological Niches · Paper 2 — Free Biology SL Practice Questions

The intertidal zone of a rocky shore in the Pacific Northwest is home to two species of barnacle: Balanus glandula (acorn barnacle) and Chthamalus dalli (thatched barnacle). Balanus grows faster and outcompetes Chthamalus in the lower intertidal zone but is less tolerant of desiccation during low tide. Chthamalus can survive higher on the shore where air exposure is longer. Researchers measured the fundamental niche of each species in the laboratory by growing them across a gradient of submersion times. - Balanus fundamental niche: $8$–$24$ hours submersion per day - Chthamalus fundamental niche: $2$–$18$ hours submersion per day Researchers then cleared a section of the mid-intertidal zone (average $12$ hours submersion per day) of all barnacles and monitored recolonisation over two years. After two years, only Balanus was present in the cleared zone.

In a freshwater lake in Uganda, two species of cichlid fish (Haplochromis nyererei and Haplochromis pyrrhocephalus) coexist. Both feed on zooplankton but have different mouth morphologies allowing prey capture at different depths. Researchers measured stomach contents of 50 individuals of each species across four depth zones. The table shows the percentage of each species' total feeding time spent in each zone. Depth zone — H. nyererei — H. pyrrhocephalus $0\text{–}2\,\text{m}$ — $10\%$ — $45\%$ $2\text{–}4\,\text{m}$ — $25\%$ — $35\%$ $4\text{–}6\,\text{m}$ — $40\%$ — $15\%$ $6\text{–}8\,\text{m}$ — $25\%$ — $5\%$

A study was conducted in a temperate deciduous forest in Vermont, USA, to investigate the ecological niches of three sympatric warbler species: the Blackburnian Warbler (Setophaga fusca), the Black-throated Green Warbler (Setophaga virens), and the Yellow-rumped Warbler (Setophaga coronata). Researchers recorded foraging height and the percentage of time spent foraging on different tree parts over three breeding seasons. Table 1: Foraging data for three warbler species Species — Mean foraging height $\pm$ SD (m) — Needles/leaves (%) — Branches (%) — Trunks (%) Blackburnian — $14.2 \pm 1.8$ — 78 — 18 — 4 Black-throated Green — $9.7 \pm 2.1$ — 62 — 30 — 8 Yellow-rumped — $5.3 \pm 2.5$ — 45 — 38 — 17