Saturday, 6 August 2011

Honours Project Overviews – for studies beginning in 2012

In the Morgan Plant Ecology Lab, we explore questions relating to species diversity, environmental gradients, vegetation dynamics, extinction processes, disturbance and land use. Much of our work is conducted in the threatened grassy ecosystems of lowland Australia, as well as alpine vegetation. We focus on the importance of plant demography and niche processes in community assembly, and use plant traits to predict vegetation responses to key drivers such as climate, habitat loss and invasions. I am interested to talk to students about their own ideas, but provide some general project themes as examples of projects in 2012.

Paying the extinction debt – what are the plant traits / attributes of species that have already paid the ‘debt’ in fragmented ecosystems relative to those species that have yet to do so?
Habitat loss and degradation pose a major threat to biodiversity. Extensive loss of habitat area can result in local extinction of specialist species. However, many species exhibit a delayed response to environmental changes due to the slow intrinsic dynamics of populations, resulting in an extinction debt. Repeat surveys can be used to directly assess changes in habitat characteristic species by comparing historical and current inventories in fragmented grasslands with the aim to characterize the species that constitute extinction debt. In communities in which extinction debt is already paid, locally extinct and persistent species might be characterised with different life-history trait values. If so, results can be applied to less degraded grasslands, where the extinction debt is not yet paid, to determine those species most vulnerable to future extinction.

Identifying resilience to a warming climate and capacity for adaptive management in Australian alpine plant species: a seed-based approach
The Australian Alps are heritage listed, one of 11 Australian centres of plant diversity, and one of the world’s 187 biodiversity hotspots. Already experiencing reduced snow cover, increased temperatures and elevated CO2, they have been identified by the IPCC as critically vulnerable to climate change. Alpine areas occur in narrow altitudinal bands; thus, plant species and communities have limited scope for movement to cooler, wetter, refuges. One of the major determinants of how climate change will affect alpine plant species will be their ability to reproduce and recruit under novel environmental conditions.

We aim to identify resilience to a warming climate in alpine ecosystems by focusing on seed traits. We will collate baseline information on alpine seed regeneration requirements (physiological dormancy mechanisms, thermal germination niche breadth) to summarise current understanding and make predictions. We will expand knowledge on alpine seed and germination traits using key predictors of resilience such as life form (grasses, forbs, shrubs), habitat breadth (narrow versus broad), population size (rare, common), and phylogeny. We will select alpine species, contrasting one or more of the above characteristics, for assessment of seed production, dormancy (such as stratification requirements), thermal germination niche breadth (variation around optimal germination using temperature gradient plates) and variation in these traits among populations.
The role of dominant species in the structure and function of ecosystems
Many communities are characterized by uneven distributions of species. Understanding the processes underlying these patterns and their implications for community dynamics and ecosystem function is a central endeavor of ecology. Often in communities only a few species are very common (or dominant), whereas a majority of species occur at moderate or low abundance (subordinate or rare). Dominant species generally garner a disproportionate share of resources, contribute most to productivity and other ecosystem functions, and are consistently present in the community over time. Rare and uncommon species, on the other hand, are collectively the most diverse component of the community, but generally contribute less to ecosystem functioning (although there are exceptions, e.g., legumes) and often experience high levels of turnover.

Our research has shown that dominant species (i.e. C4 grasses like Kangaroo Grass) can strongly influence diversity, and it is through the impacts of disturbances on their abundance that variation in community attributes and ecosystem processes in space and time are observed. These dominant species likely play a central role in the maintenance of ecosystem function and the dominant species are important in determining resistance of communities to invasion. Our research seeks to (a) understand why these species are dominant (i.e. trait-based approaches) and (b) gain a more general understanding their role in ecosystems.

Friday, 5 August 2011

New Honours Student in the Lab

Citra Jewson-Brown has joined the Lab.

Citra will investigate how herbivory affects fitness in snow gum seedlings. Upslope advance of snow gums in the Australian alps are thought to be mostly due to increases in temperature, but we think herbivory also plays a role.

The basic starting point for this project is the observation that herbivory on eucalypt saplings varies dramatically in the high country. Some saplings (e.g. near treeline) have high levels of defoliation whereas other seedlings (in subalpine woodlands and snowplains) do not suffer as much. Why? Do ants ‘defend’ saplings against defoliation – many saplings have ant nests at the base of saplings and these tend scale insects. Hence, as elsewhere, perhaps the ants 'protect' the scale and in the process, defend saplings from defoliators.
There are three basics steps that will be undertaken in this project:
Step 1 – quantify the nature of herbivory across sites that vary in altitude, within a plant, within a season
Step 2 – quantify the abundance of ants and scale on saplings – and how this varies with altitude
Step 3 – experiment by excluding ants (and/or scale) from a number of saplings and compare to unexcluded saplings (where there is an obvious utilization)
What we hope to learn – controls on eucalypt ‘performance’  (a key species in the alpine) are driven by factors other than climate; one may be an interaction with another key species (ants) which may themselves be affected by climate and non-climate factors (scale).