Wednesday, 14 September 2011

The David Ashton Scholarship winner announced

Citra Jewson-Brown was recently awarded the David Ashton Scholarship. Congratulations!
The award recognises the most outstanding new Honours students undertaking research in the field of plant ecology in the Department of Botany at La Trobe University. It is named after Dr David Ashton, a Victorian plant ecologist who spent his entire working life trying to understand the regeneration and succesional dynamics of Mountain Ash forests. He also worked with students in the alpine regions of Victoria, so would be chuffed to know that Citra intends to focus her thesis on high mountain ecology.
Citra will work with Dr John Morgan on insect herbivory in high altitude populations of Snow Gum (Eucalyptus pauciflora). In particular, she is keen to quantify how herbivory varies within and between populations of Snow Gum. This will likely involve an interaction between environment (altitude) and "provenance".

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).

Tuesday, 10 May 2011

Honours Students 2010/11

Two Honours students undertook their thesis in the Plant Ecology Lab under the supervision of Dr John Morgan in 2010/11. Below is a summary of their findings.
Tara Angevin:
How does functional diversity change with land-use intensification?
Biodiversity loss, due to anthropogenic land use, is of increasing concern, as human activities have the potential to erode the ecosystem processes and services important to ecosystem functioning. While many studies have explored the impacts of disturbance on species richness, a neglected aspect of biodiversity studies is functional trait diversity (the degree to which species differ from one another in relation to their functional traits). Plant functional traits have been recognised as valuable tools for understanding the mechanisms driving community composition, as the range of functions provided by a plant community is thought to be dependent on the diversity of trait states and the species that express them.

Many studies assume that increasing disturbance will lead to a loss of species richness, in turn driving a loss of functional diversity, consistent with the sampling effect hypothesis. There is evidence to suggest that there are numerous trajectories possible for the species richness and functional diversity relationship, many of which deviate considerably from the typical sampling effect.

This trait-based study investigated the relationship between species richness and functional diversity using a space-for-time chronosequence method, to determine whether the loss of species richness would automatically result in the loss of functional diversity. Functional trait diversity and species richness were linked to one another using multi-dimensional trait amalgams. Three novel functional diversity indices, Functional richness (FRic), Functional evenness (FEve) and Functional divergence (FDiv) were applied to determine the level of functional space occupied by the plant community. Multi-trait diversity indices look at the interaction of traits in functional space, rather than just looking at the diversity of trait states.
In addition, the current study aimed to investigate which traits help underpin the changes observed across a disturbance gradient, through single trait analysis.

Floristic composition and functional trait signatures of both native and exotic species were compared between three disturbance treatments; disturbance categories were stratified according to information available based on time- since- disturbance and disturbance type. Lastly, this study aimed to determine whether plant functional traits are a useful currency to help underpin the patterns in species richness observed across the various disturbance gradients.

These studies provide evidence to suggest that species richness and functional diversity are not always correlated, and report that disturbance can lead to an increase in species richness (both native and exotic) yet no corresponding shift in species functional attributes. No significant differences in functional diversity was observed between low, moderate and high disturbance treatments when aggregated in multi-trait analysis, though results did show slight shifts in functional trait diversity, when analysed individually. Leaf area was reported to increase with increasing disturbance and plant height was shown to decrease with increasing disturbance. This type of relationship is not frequently reported in current literature and provides evidence that species richness and functional diversity can be decoupled and that novel communities may reassemble following disturbance events.

It was concluded that species richness and functional diversity are dependent on a number of factors, such as the size of the species pool, competitive interactions, conditions present within a specific type of a system (ie/site productivity) and the type of disturbance inposed onto a system. These studies also indicate that disturbance intensity was perhaps not severe enough to impact on environmental filters or there has been insufficient time to see a shift in functional diversity. 

James Vincent
What evidence is there for upslope migration of the obligate-seeder Alpine Ash (Eucalyptus delegatensis) after fire?

Current models predict mountain species will migrate upslope in response regional climate warming. Evidence from the literature supports the upslope advance of species but also demonstrates that, in many cases, migration lags behind climate change. This study focused on changes in the upper distribution of Eucalyptus delegatensis (Alpine Ash) at the montane/sub-alpine after a recent landscape-scale fire in the Australian Alps.

Eucalyptus delegatensis only recruits via seed after crown-scorching fire and is considered a long-term occupant of a site 2 - 4 years after regeneration. Consequently, Alpine Ash can only track climate and migrate upslope following fire events. This study demonstrated the upper distribution of E. delegatensis shifted only 4 - 6 m in altitude following fire in 2003 (last burnt in 1939), despite a potential increase of 130 m in altitude based on local temperature increases. It is hypothesised that upslope establishment was constrained by either limited seed dispersal or unsuitable sites for regeneration above the boundary.

To untangle these potential mechanisms, a seed sowing (to overcome dispersal limitation) and transplant experiment (to determine effects of local site factors on early survival and growth) was conducted at Lake Mountain. Two age classes of Alpine Ash (<3 months and 18 months old) grew successfully, with low mortality, 100 m above the boundary. A slight non-significant trend toward greater growth was detected below the boundary. Therefore, it is proposed that Alpine Ash may be dispersal-limited in years favourable for growth but safe-site limited in years of more extreme climatic conditions. Further work is required, however, to substantiate this hypothesis.

In the context of the future migration potential of Alpine Ash, the species is unlikely to track changes in climate due to the requirement of fire for recruitment, coupled with long intervals between fire events, a poor dispersal ability, and reliance on favourable growing conditions after fire. It is proposed that the migration potential of a species’ may be ranked according to its climatic and edpahic requirements and traits such as dispersal ability, generation time and germination cues; specialists and species of low dispersal capacity and long generation time are more likely to lag behind changes in climate.