Growth estimates of young‐of‐the‐year broadnose sevengill shark, Notorynchus cepedianus , a top predator with poorly calcified vertebrae

Effects of fish on plankton dynamics: a theoretical analysis

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f00-018 ◽

2000 ◽

Vol 57 (6) ◽

pp. 1208-1219 ◽

Cited By ~ 52

Author(s):

Marten Scheffer ◽

Sergio Rinaldi ◽

Yuri A Kuznetsov

Keyword(s):

Phytoplankton Biomass ◽

Food Limitation ◽

Homoclinic Bifurcation ◽

The Other ◽

Fish Density ◽

Nutrient Concentrations ◽

Field Observations ◽

Top Predator ◽

Predator Prey ◽

Young Of The Year

We present an expansion of a classical minimal Daphnia-algae model to account for effects of fish as a top predator. Our analyses suggest that in most situations, the plankton should show hysteresis in response to predation pressure by fish. Thus, there exist two distinct regimes, one in which Daphnia is controlled (overexploited) by fish and phytoplankton biomass is high and another in which Daphnia is relatively unaffected (underexploited) by planktivores and algae are controlled by Daphnia. Switches from one regime to the other occur abruptly at a critical fish density. This is in line with field observations and experimental results. Our model predicts that the critical fish density for Daphnia collapse is higher in systems with higher ambient nutrient concentrations. The model also shows how intrinsic predator-prey oscillations in the planktonic system can facilitate the switch to the algal-dominated regime where Daphnia is controlled by fish. In terms of dynamical systems theory, this switch happens through a homoclinic bifurcation. In biological terms, Daphnia collapses due to food limitation and is subsequently overexploited by fish. This is indeed the sequence of mechanisms observed at the end of the spring clearwater phase in lakes where Daphnia is absent during the summer when the biomass of young-of-the-year planktivorous fish becomes high.

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Prey-field use by a Southern Ocean top predator: enhanced understanding using integrated datasets

Marine Ecology Progress Series ◽

10.3354/meps11203 ◽

2015 ◽

Vol 526 ◽

pp. 169-181 ◽

Cited By ~ 10

Author(s):

M Bedford ◽

J Melbourne-Thomas ◽

S Corney ◽

T Jarvis ◽

N Kelly ◽

...

Keyword(s):

Southern Ocean ◽

Top Predator

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Testing ecological release as a compensating mechanism for mass mortality in a keystone predator

Marine Ecology Progress Series ◽

10.3354/meps13227 ◽

2020 ◽

Vol 637 ◽

pp. 59-69 ◽

Cited By ~ 1

Author(s):

J Sullivan-Stack ◽

BA Menge

Keyword(s):

Community Dynamics ◽

Limiting Factor ◽

Sea Star ◽

Top Predator ◽

Oregon Coast ◽

Ecological Release ◽

Keystone Predator ◽

Pisaster Ochraceus ◽

Wasting Syndrome

Top predator decline has been ubiquitous across systems over the past decades and centuries, and predicting changes in resultant community dynamics is a major challenge for ecologists and managers. Ecological release predicts that loss of a limiting factor, such as a dominant competitor or predator, can release a species from control, thus allowing increases in its size, density, and/or distribution. The 2014 sea star wasting syndrome (SSWS) outbreak decimated populations of the keystone predator Pisaster ochraceus along the Oregon coast, USA. This event provided an opportunity to test the predictions of ecological release across a broad spatial scale and determine the role of competitive dynamics in top predator recovery. We hypothesized that after P. ochraceus loss, populations of the subordinate sea star Leptasterias sp. would grow larger, more abundant, and move downshore. We based these predictions on prior research in Washington State showing that Leptasterias sp. competed with P. ochraceus for food. Further, we predicted that ecological release of Leptasterias sp. could provide a bottleneck to P. ochraceus recovery. Using field surveys, we found no clear change in density or distribution in Leptasterias sp. populations post-SSWS, and decreases in body size. In a field experiment, we found no evidence of competition between similar-sized Leptasterias sp. and P. ochraceus. Thus, the mechanisms underlying our predictions were not in effect along the Oregon coast, which we attribute to differences in habitat overlap and food availability between the 2 regions. Our results suggest that response to the loss of a dominant competitor can be unpredictable even when based in theory and previous research.

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