[MARMAM] New publication on impacts of changing prey availability on porpoise populations

Cara Gallagher carag16 at gmail.com
Thu Dec 9 02:36:48 PST 2021

 Hello MARMAM folks!

My co-authors and I are delighted to share with you our new paper assessing
the impacts of potential climate-induced changes in prey size and spatial
aggregation on harbor porpoise populations, which was recently published in
the Journal of Animal Ecology.

Gallagher, C.A., Chimienti, M., Grimm, V. and Nabe‐Nielsen, J., 2021.
Energy‐mediated responses to changing prey size and distribution in marine
top predator movements and population dynamics. Journal of Animal Ecology.

You can also check out the accompanying video abstract here:

Please do not hesitate to contact me for a PDF or if you have any questions
/ comments (gallagher at uni-potsdam.de).

All the best,
Cara Gallagher

1. Climate change is modifying the structure of marine ecosystems,
including that of fish communities. Alterations in abiotic and biotic
conditions can decrease fish size and change community spatial arrangement,
ultimately impacting predator species which rely on these communities. To
conserve predators and understand the drivers of observed changes in their
population dynamics, we must advance ou understanding of how shifting
environmental conditions can impact populations by limiting food available
to individuals.
2. To investigate the impacts of changing fish size and spatial aggregation
on a top predator population, we applied an existing agent-based model
parameterized for harbour porpoises, Phocoena phocoena, which represents
animal energetics and movements in high detail. We used this framework to
quantify the impacts of shifting prey size and spatial aggregation on
porpoise movement, space use, energetics and population dynamics.
3. Simulated individuals were more likely to switch from area-restricted
search to transit behaviour with increasing prey size, particularly when
starving, due to elevated resource competition. In simulations with highly
aggregated prey, higher prey encounter rates counteracted resource
competition, resulting in no impacts of prey spatial aggregation on
movement behaviour.
4. Reduced energy intake with decreasing prey size and aggregation level
caused population decline, with a 15% decrease in fish length resulting in
total population collapse. Increasing prey consumption rates by 42.8 ± 4.5%
could offset population declines; however, this increase was 21.3 ± 12.7%
higher than needed to account for changes in total energy availability
alone. This suggests that animals in realistic seascapes require additional
energy to locate smaller prey which should be considered when assessing the
impacts of decreased energy availability.
5. Changes in prey size and aggregation influenced movements and population
dynamics of simulated harbour porpoises, revealing that climate-induced
changes in prey structure, not only prey abundance, may threaten predator
populations. We demonstrate how a population model with realistic animal
movements and process-based energetics can be used to investigate
population consequences of shifting food availability, such as those
mediated by climate change, and provide a mechanistic explanation for how
changes in prey structure can impact energetics, behaviour and ultimately
viability of predator populations.

Cara Gallagher
Postdoctoral researcher
Department of Plant Ecology and Conservation Biology
University of Potsdam
Potsdam, Germany
+49 015175471396 tel.
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