Research fellow position: Adaptive Dynamics Modeller

  • Level A, research-only academic
  • $64,450 to $87,471 pa + 9.5% superannuation
  • Full-time, starting late 2017
  • Two-year, fixed-term
  • Monash University Clayton campus

The Centre for Geometric Biology is currently seeking to recruit an experienced theoretical biologist experienced in adaptive dynamics modelling.

As the postdoctoral researcher, you will use adaptive dynamics modelling approaches to explore the drivers and consequences of body size evolution. Working with other researchers in the Centre for Geometric Biology, you will parameterise models based on empirical findings and provide advice of key tests of model predictions.

You will further be expected to maintain consistently high research output in the form of quality publications, supervision of students, development and submission of grant proposals to external funding agencies, contribute more generally to communicating the research activities of the group, and participation in appropriate career development activities.

Key selection criteria

  1. A degree in a relevant area, utilising adaptive dynamics approaches, from a recognised university with subsequent relevant work experience, or an equivalent combination of experience and training.
  2. Demonstrated experience in developing theoretical models in fundamental ecology or empirical research using cutting-edge quantitative approaches.
  3. Demonstrated ability to undertake outstanding research; with a high quality research publication record in recognised journals.
  4. Ability to solve problems by using discretion, innovation and the exercise of high level diagnostic skills within areas of functional responsibility or professional expertise.
  5. Excellent written communication and verbal communication skills with proven ability to effectively analyse information and produce clear, succinct reports and documents which requires interaction with others.
  6. Demonstrated planning and organisational skills, with the ability to prioritise multiple tasks and set and meet deadlines.
  7. Demonstrated awareness of the principles of confidentiality, privacy and information handling.
  8. Demonstrated ability to effectively work independently and in a multidisciplinary team to make a contribution to research and scholarship.
  9. Experience of, or willingness to work on, marine systems.
  10. A demonstrated understanding of questions in fundamental ecology and/or evolution.

Enquiries to Professor Dustin Marshall on +61 3 9902 4449

For more information, or to apply, refer to the Monash University website

Research fellow position: Life History Empiricist

  • Level A, research-only academic
  • $64,450 to $87,471 pa + 9.5% superannuation
  • Full-time, starting late 2017
  • Two-year, fixed-term
  • Monash University Clayton campus

The Centre for Geometric Biology is currently seeking to recruit an experienced zooplankton biologist.

You will further be expected to maintain consistently high research output in the form of quality publications, supervision of students, development and submission of grant proposals to external funding agencies, contribute more generally to communicating the research activities of the group, and participation in appropriate career development activities.

 

Key selection criteria

  1. A PhD on zooplankton or a relevant area, from a recognised university with subsequent relevant work experience, or an equivalent combination of experience and training.
  2. Demonstrated experience in developing theoretical models in fundamental ecology or empirical research using cutting-edge quantitative approaches.
  3. Demonstrated ability to undertake outstanding research; with a high quality research publication record in recognised journals.
  4. Ability to solve problems by using discretion, innovation and the exercise of high level diagnostic skills within areas of functional responsibility or professional expertise.
  5. Excellent written communication and verbal communication skills with proven ability to effectively analyse information and produce clear, succinct reports and documents which requires interaction with others.
  6. Demonstrated planning and organisational skills, with the ability to prioritise multiple tasks and set and meet deadlines.
  7. Demonstrated awareness of the principles of confidentiality, privacy and information handling.
  8. Demonstrated ability to effectively work independently and in a multidisciplinary team to make a contribution to research and scholarship.
  9. Experience of, or willingness to work on, marine systems.
  10. A demonstrated understanding of questions in fundamental ecology and/or evolution.

Enquiries to Professor Dustin Marshall on +61 3 9902 4449

For more information, or to apply, refer to the Monash University website

Eco-energetic consequences of evolutionary shifts in body size

Authors: Martino E Malerba, Craig R White, and Dustin J Marshall

Published in: Ecology Letters

Abstract

Size imposes physiological and ecological constraints upon all organisms. Theory abounds on how energy flux covaries with body size, yet causal links are often elusive.

As a more direct way to assess the role of size, we used artificial selection to evolve the phytoplankton species Dunaliella tertiolecta towards smaller and larger body sizes.

Within 100 generations (c. 1 year), we generated a fourfold difference in cell volume among selected lineages. Large-selected populations produced four times the energy than small-selected populations of equivalent total biovolume, but at the cost of much higher volume-specific respiration. These differences in energy utilisation between large (more productive) and small (more energy-efficient) individuals were used to successfully predict ecological performance (r and K) across novel resource regimes.

We show that body size determines the performance of a species by mediating its net energy flux, with worrying implications for current trends in size reduction and for global carbon cycles.

Malerba ME, White CR, Marshall DJ (2017) Eco-energetic consequences of evolutionary shifts in body size, Ecology Letters, PDF DOI 

Discussion group with Professor Troy Day

When: 12.00 noon to 2.00 pm, Wednesday 22 November 2017

Where: Sanson Room (22 G01/02), Rainforest Walk, Monash University.

We are delighted to welcome Professor Troy Day from Queen’s University in Ontario, Canada who will be joining our discussion group.

Troy will give a brief presentation about “The evolutionary advantages of haploid versus diploid microbes in nutrient poor environments”. Troy will talk about the nutrient limitation hypothesis and how theoretical predictions compare with empirical observations.

Postdocs Martino Malerba and Giulia Ghedini will also be giving short presentations about their latest research on artificial selection and energy budgets of phytoplankton and invertebrates.

Presentations will be followed by general discussion and we invite you to join us for this discussion.

For further details please contact Liz Morris.

An experimental demonstration of the effect of competition on energy budgets

How much an individual organism can grow depends on both the amount of energy acquired (from food consumption) and the energy expended on respiration (metabolic rate).  Increasing population densities can affect the availability of energy by increasing competition for resources (such as food) which can, in turn, affect the rates at which individuals acquire and expend energy.

Post-doctoral fellow, Giulia Ghedini, and colleagues Craig White and Dustin Marshall are interested in whether feeding rates and metabolic rates change in the same way when population densities increase. They wanted to explore why individuals typically reach smaller sizes in denser populations while knowing that growth ultimately depends on how rates of energy intake change relative to rates of energy expenditure.

The research team considered four possible scenarios where the rates of feeding and metabolism varied and which would have different outcomes in terms of the energy available for growth (see figure). Few studies have considered both these rates at the same time and so the ways in which both intake (feeding) and expenditure (metabolism) are affected by density remains unclear making it difficult to predict which scenario would apply.

The research team considered four possible scenarios where the rates of feeding and metabolism varied and which would have different outcomes in terms of the energy available for growth.

Giulia and colleagues used the colonial bryozoan Bugula neritina as a study organism and experimentally created populations of different densities by settling increasing numbers of larvae on experimental plates. After metamorphosis these larvae developed into adult colonies that were grown in the field at the different population densities ranging from 1 to 30 individual colonies per plate.

The different populations of Bugula were supplied with equal amounts of food (a single celled alga) and feeding rates were calculated after three hours.  Metabolic rates were calculated by measuring changes in percentage oxygen over the same period of time (three hours) and the ‘scope for growth’ of each individual colony was calculated by subtracting energy expenditure (metabolism) from energy intake (feeding).

Giulia and her colleagues found that while both feeding rates and metabolic rates decreased with increasing population densities, energy gains from food intake decreased faster than the energy expended on metabolism, reducing the amount of energy available for growth (scenario 3 on figure).  This explains why individual growth and reproductive output decrease in denser populations.

What is more, the researchers have also demonstrated that the difference between energy intake and expenditure at the individual colony level could predict the average body size that colonies reached in populations of varying densities.

This research was published in the journal Ecology.

Net-energy gain in phytoplankton cells is dependent on cell size, light, and population density

While there have been many studies on the effects of organism size on energy use, there are few studies that also examine rates of energy acquisition. The overall effect of size on the energy budget of an organism will depend on how size affects both energy gain and use, that is, the net-energy gain.

To improve our understanding on this topic, postdoctoral fellow Martino Malerba has been working with colleagues Craig White and Dustin Marshall to investigate how size affects net-energy gain in single celled phytoplankton species at different light intensities and population densities.

They used 21 species of phytoplankton from seven phyla, spanning four orders of magnitude in cell volume. All species were measured across six light intensities and four different population densities. Net-energy gain was calculated by fitting non-linear models to changes in percentage oxygen saturations across all treatment combinations, which then allowed researchers to calculate rates of photosynthesis and respiration.

The team examined 21 species of phytoplankton from seven phyla.

Martino and colleagues found that increasing the size of a cell or decreasing population density produced similar proportional increases in both rates of energy production (via photosynthesis) and respiration.

Larger cells produced more energy but also had higher energy costs due to respiration. Increasing population density decreased both photosynthesis and respiration rates. While the reduction in photosynthetic activity may be explained by an increase in shading by suspended cells at higher population densities, this does not explain why increased population density also decreased respiration rates in the dark.

It is possible that reducing metabolic rates at increasing population densities is an adaptive strategy that reduces the minimum requirements of a cell and improves fitness when resources are limited.

Finally, it is increasingly apparent that global temperature increases are reducing body sizes worldwide, particularly of aquatic organisms. Results from this study suggest that future phytoplankton communities dominated by smaller species should display higher size-specific rates of net-energy gain. This would mean current rates of carbon storage in aquatic environments are likely to increase.

This research is published in the journal Ecology.

Does energy flux predict density-dependence? An empirical field test

Authors: Giulia Ghedini, Craig R White, and Dustin J Marshall

Published in: Ecology

Abstract

Changes in population density alter the availability, acquisition and expenditure of resources by individuals, and consequently their contribution to the flux of energy in a system.

Whilst both negative and positive density-dependence have been well studied in natural populations, we are yet to estimate the underlying energy flows that generate these patterns and the ambivalent effects of density make prediction difficult.

Ultimately, density-dependence should emerge from the effects of conspecifics on rates of energy intake (feeding) and expenditure (metabolism) at the organismal level, thus determining the discretionary energy available for growth.

Using a model system of colonial marine invertebrates, we measured feeding and metabolic rates across a range of population densities to calculate how discretionary energy per colony changes with density and test whether this energy predicts observed patterns in organismal size across densities.

We found that both feeding and metabolic rates decline with density but that feeding declines faster, and that this discrepancy is the source of density-dependent reductions in individual growth. Importantly, we could predict the size of our focal organisms after 8 weeks in the field based on our estimates of energy intake and expenditure.

The effects of density on both energy intake and expenditure overwhelmed the effects of body size; even though higher density populations had smaller colonies (with higher mass-specific biological rates), density effects meant that these smaller colonies had lower mass-specific rates overall.

Thus, to predict the contribution of organisms to the flux of energy in populations it seems necessary not only to quantify how rates of energy intake and expenditure scale with body size, but also how they scale with density given that this ecological constraint can be a stronger driver of energy use than the physiological constraint of body size.

Ghedini G, White CR, Marshall DJ (2017) Does energy flux predict density-dependence? An empirical field test. Ecology, PDF DOI

Phytoplankton size-scaling of net-energy flux across light and biomass gradients

Authors: Martino E Malerba, Craig R White, and Dustin J Marshall

Published in: Ecology, (early view)

Abstract

Changes in population density alter the availability, acquisition and expenditure of resources by individuals, and consequently their contribution to the flux of energy in a system.

Whilst both negative and positive density-dependence have been well studied in natural populations, we are yet to estimate the underlying energy flows that generate these patterns and the ambivalent effects of density make prediction difficult. Ultimately, density-dependence should emerge from the effects of conspecifics on rates of energy intake (feeding) and expenditure (metabolism) at the organismal level, thus determining the discretionary energy available for growth.

Using a model system of colonial marine invertebrates, we measured feeding and metabolic rates across a range of population densities to calculate how discretionary energy per colony changes with density and test whether this energy predicts observed patterns in organismal size across densities.

We found that both feeding and metabolic rates decline with density but that feeding declines faster, and that this discrepancy is the source of density-dependent reductions in individual growth. Importantly, we could predict the size of our focal organisms after 8 weeks in the field based on our estimates of energy intake and expenditure. The effects of density on both energy intake and expenditure overwhelmed the effects of body size; even though higher density populations had smaller colonies (with higher mass-specific biological rates), density effects meant that these smaller colonies had lower mass-specific rates overall.

Thus, to predict the contribution of organisms to the flux of energy in populations it seems necessary not only to quantify how rates of energy intake and expenditure scale with body size, but also how they scale with density given that this ecological constraint can be a stronger driver of energy use than the physiological constraint of body size.

Malerba ME, White C, Marshall DJ (2017) Phytoplankton size-scaling of net-energy flux across light and biomass gradients. Ecology PDF DOI