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In this paper the authors expand greatly on previous work by amalgamating …


Biology Articles » Ecology » Complex interplay between intrinsic and extrinsic drivers of long-term survival trends in southern elephant seals » Figures

Figures
- Complex interplay between intrinsic and extrinsic drivers of long-term survival trends in southern elephant seals

Figures

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Figure 1 Macquarie Island southern elephant seal abundance trends (1951 – 2003) and the Southern Oscillation Index over that period. (Top panel) Abundance trends of the isthmus population of breeding females at Macquarie Island from 1951 to 2003. Two main census periods emerge (1) between 1951 and 1960 (the relatively high-density era) and (2) from 1993 to 1999 (the low-density era). (B) El Niño-Southern Oscillation (ENSO) conditions as measured by the Southern Oscillation Index (SOI) anomaly over the elephant seal foraging period from January to October between 1950 and 2001. High positive values of the SOI anomaly indicate El Niño conditions, and high negative values indicate La Niña conditions.

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Figure 2 Rate of population change versus abundance. Intrinsic rate of population change (r = log [Nt+1/Nt]) versus Nt (abundance) for the breeding female southern elephant seal population at the Macquarie Island isthmus during (A) the high-density era (1951–1960) and (B) the low-density era (1993–1999). Five population dynamics models (RW = random walk, EX = exponential growth, RL = Ricker-logisitc growth, GL = Gompertz-logistic growth and TL = θ-logistic growth; see Methods) were fitted to the relationship of r versus Nt. The sum of the Akaike Information Criterion (corrected for small sample sizes – AICc) weights over the three density-dependent models considered (RL, GL and TL) show 77.4 % strength of evidence for density dependence during the high-density era (A) and 89.3 % support for the phenomenon during the low-density era (B).

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Figure 3 Apparent survival probability of yearling southern elephant seals versus the Southern Oscillation Index and population size. Model-averaged, time-variant estimates of mean apparent survival () for yearling southern elephant seals at Macquarie Island plotted as a function of (A) the Southern Oscillation Index (SOI) anomaly over the mother's previous foraging trip (January to October) between 1950 and 2001 (high positive values of the SOI anomaly indicate El Niño conditions; high negative values indicate La Niña conditions), and (B) the number of breeding females counted on the isthmus of Macquarie Island that year.

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