Model simulations of growth (whole individual – total volume) and defence levels (whole individual – pooled gland cell volume) under low (A) and moderate (B) light (n = 40 random individuals).

<p>(A) Under low light (10 µE) a negative correlation across individuals occurs with decreasing pooled gland cell volume in larger (more frequently branched) individuals. (B) Under moderate light (35 µE) a positive correlation is driven by greater variation in cell division between individuals producing individuals of different sizes, independent of branch frequency. Significant correlations are shown (<i>P</i><0.05).</p

Model parameters that describe the cellular growth patterns of <i>Asparagopsis armata</i>.

<p>Parameters are derived from cellular data for individuals cultured under low (10 µE) and moderate (35 µE) light levels.</p

Empirical correlations between total metabolite concentration and growth rate (A) and individual size (B) for 15 families of clones under both low light (solid circles) and moderate light (no fill).

<p>Solid lines show significant negative correlations (<i>P</i><0.05), dotted lines show positive trends (<i>P</i> = 0.13 A, <i>P</i> = 0.07 B).</p

Empirical means of the percent volume (+1 SE) of the algal filament that is occupied by gland cells for apical and mature cells along the axis.

<p>Results represent the combined treatments for algae cultured under 10 µmol photons m⁻² s⁻¹ and 35 µmol photons m⁻² s⁻¹. <i>N</i> = 10 individuals per treatment.</p

Key model simulations distinguishing low light (10 µE, dashed lines) and moderate light (35 µE, solid lines).

<p>(A) Ontogenetic trajectory of the relative investment in defence along a filament. (B) Pooled gland cell volume versus whole individual volume based on mean branch frequency (low = 16 and moderate = 11 cells per branch). The pooled gland cell volume (%) indicates the overall level of defence. (C) Pooled gland cell volume as a percentage of whole individual volume related to branch frequency. Higher branch frequency (left) leaders to lower overall levels of defence in an individual. Note that the relative difference between light levels decreases with decreased branch frequency (left to right).</p

Habit of the filamentous tetrasporophyte of <i>Asparagopsis armata</i>.

<p>Outside of branching events, cell division only occurs at the single apical cell on each axis. Gland cells are first observed approximately 3–5 cells from the apical cell. Inset: the repeating unit of cellular growth is a tier comprised of 7 cells. Each cell tier (a cylinder of length “b” and diameter “c”) consists of 3 pericentral cells surrounding a single axial cell, and each pericentral cell contains a single refractile gland cell (a sphere of diameter “a”). Scale bar, 200 µm.</p

Resource allocation across the growth axis.

<p>ANOVA results for the percentage of cell tier volume that is occupied by gland cells in apical and mature regions for algae cultured under low (10 µE) and moderate (35 µE) light. Data were log-transformed prior to analysis.</p

Collapse of a Marine Mammal Species Driven by Human Impacts

<div><p>Understanding historical roles of species in ecosystems can be crucial for assessing long term human impacts on environments, providing context for management or restoration objectives, and making conservation evaluations of species status. In most cases limited historical abundance data impedes quantitative investigations, but harvested species may have long-term data accessible from hunting records. Here we make use of annual hunting records for Caspian seals (<em>Pusa caspica</em>) dating back to the mid-19^th century, and current census data from aerial surveys, to reconstruct historical abundance using a hind-casting model. We estimate the minimum numbers of seals in 1867 to have been 1–1.6 million, but the population declined by at least 90% to around 100,000 individuals by 2005, primarily due to unsustainable hunting throughout the 20^th century. This collapse is part of a broader picture of catastrophic ecological change in the Caspian over the 20^th Century. Our results combined with fisheries data show that the current biomass of top predators in the Caspian is much reduced compared to historical conditions. The potential for the Caspian and other similar perturbed ecosystems to sustain natural resources of much greater biological and economic value than at present depends on the extent to which a number of anthropogenic impacts can be harnessed.</p> </div

The population growth rate of the Caspian seal population from 1867 to 2006 has fluctuated significantly because of the variable hunting pressure.

<p>The population growth rate of the Caspian seal population from 1867 to 2006 has fluctuated significantly because of the variable hunting pressure.</p

Estimated minimum total female population size (solid line) and the number adult females (dashed line) in the Caspian for the period 1867–2005 as based on historical hunting records (<b>Fig. 1</b>).

<p>The hunt during the 1960s led to a rapid decline in population size.</p