Scientific contributions to ecological knowledge and conservation of wildlife

Australia through statistical design, the development of statistical models, and

effective

collaboration with ecologists. Significantly, these contributions have contributed across several

biological research areas that are outlined in the following sections.

1.5.1 The design of large-scale quasi-experiments in landscape ecology: Chapters 2, 3, 4,

and 5, and Appendix A

The process of design often involves extensive collaboration between statisticians and

ecologists. As previously mentioned, a lengthy iterative process is required where ecological

questions and different designs are considered.

1.5.2 Forest ecology: Chapters 3 and 9

In Chapter 3 there was a focus on comparing bird responses between remnant patch types after

many years of forest fragmentation. The findings indicated that irrespective of size and shape,

all fragments have significant conservation value. In addition, smaller birds with smaller

clutches using cup nests or burrows were more likely to occupy patch-shaped remnants than

other woodland fragments types.

In the paper presented in Chapter 9, the effects of plantation development on changes in

woodland bird biodiversity were examined. The findings indicated that bird species associated

with open country and woodland environments were disadvantaged by emerging pine

plantations, whereas those benefiting included forest taxa and/or habitat generalists capable of

inhabiting pine stands and adjacent woodland patches. Additionally, some of the main attributes

of retained woodland patches associated with temporal changes in bird occupancy included the

number of boundaries with surrounding pines, the size of woodland patches, and the dominant

vegetation type of woodland patches.

1.5.3 Wildlife biology: Chapters 6 and 8

The simultaneous calling of many bird species around sunrise, commonly referred to as the

dawn chorus, is a major feature of bird communities in many environments ranging from deserts

to tropical rainforests. In the papers presented in Chapters 6 and 8, we addressed the general

question whether data obtained by birdcall recorders provide useful behavioural and ecological

information such as call rates (number of calls per bird).

1 / INTRODUCTION 21

Subsequent analysis suggested that these data provide limited but useful information about

vocal activity per bird. Automatic sound-recording data may be informative for drawing

inferences about temporal patterns in vocal activity but do not seem to be useful as a method for

estimating the abundance of birds. For most groups of birds, the observed relationships between

the number of calls recorded by sound recorders and the total number of birds detected by

human point counts were found to be statistically significant but weak. For data aggregated over

groups of sites, there was evidence of direct proportionality between the number of notes and

the abundance of birds. This was not the case for site level data. For measuring biodiversity, the

relationship between the number of species vocalising and the number detected was not directly

proportional but was nevertheless highly significant. There were many more species detected by

sound recorders than there were by human observers.

After an initial early peak of activity, there was a significant, roughly linear, decline in vocal

activity across the morning. Vocal activity persisted longer at sites located within large areas of

continuous eucalypt forest than in the strip- and patch-shaped eucalypt remnants surrounded by

extensive stands of radiata pine or at sites dominated by stands of radiata pine. There was

evidence that the pattern of persistence of vocal activity differed between the different bird

groups.

1.5.4 Restoration ecology: Chapters 5 and 7, and Appendix B

In this section, I examine different aspects of the effectiveness of revegetation on biodiversity

in agricultural landscapes. Reptiles and arboreal marsupials were shown to be less likely to

occur on farms and in landscapes with comparatively large areas of plantings (Chapter 5). It was

clear that although plantings may improve habitat conditions for some taxa, they may not

effectively offset the negative impact of native vegetation clearing for all species, especially

those reliant on old-growth woodland. Restoring suitable habitat for such species may take

decades or even centuries.

Chapter 7 contains results revealing that farms with high value remnant native vegetation

were those most likely to support declining or vulnerable bird species, although some individual

species of conservation concern occurred on farms with large plantings. Consequently, farm

management for improved bird conservation should account for the cumulative and

complementary contributions of many components of remnant native vegetation cover (e.g.,

scattered paddock trees and fallen timber) as well as areas of restored native vegetation.

Results presented in Appendix B suggest that replanting programs aimed at maximising bird

species richness may benefit from consideration of planting geometry. In particular, linking

22 1 / INTRODUCTION

strip plantings to create intersections and/or establishing block plantings appears to be superior

to isolated strips for aggregate species richness. Evidence was found of extra variation at the

farm level for species richness and derived assemblage scores, suggesting a farm-scale response.

This suggests the importance of other, often unmeasured, variables (e.g., baiting for feral

animals) at the farm level.

1.5.5 Conservation science: Chapters 10 and 11

The science of monitoring changes in biodiversity is fundamental in biological conservation.

Tracking change is essential to guide sustainable management. The statistical methodology

presented in Chapter 10 offers a flexible and practical way to assess long-term change in

situations where abundance data are scarce and difficult to gather on a sufficient scale. The

resulting analyses demonstrated the usefulness of presence–absence, volunteer-collected data

for tracking change in bird populations. A most important outcome repeated in many data sets

analysed so far was that anecdotal observation can lead to misleading conclusions.

A second paper under this theme, presented in Chapter 11, contains results from an analysis

of 76 bird species collected over 10 years in 66 patches of woodland in south-eastern Australia,

using an adaptation of the methodology outlined in Chapter 10. The results provide a more

positive outlook than do some more recent published findings from other regions and the

general view based on anecdotal reports. Declines or increases are very species-specific, rather

than related to groups defined by life history traits or other attributes. Application of the

method on many data sets again suggests that anecdotal reports can easily result in misleading

conclusions about long-term trends. Furthermore, a notable feature of bird data is the presence

of large inter-annual variation. This suggests that to determine long-term systematic changes in

bird populations, long-term data sets (e.g., >15 years) are required.

1.5.6 Landscape scale effects for several measures of biodiversity and the role of

vegetation cover in explaining these patterns: Chapters12 and 13

The paper presented in Chapter 12 provides an empirical approach to the estimation of scale

effects as well as their statistical significance. The second paper, in Chapter 13, is more focused

on comparisons between cross-sectional and temporal or direct relationships between scale

effects on individual bird species.

Species-specific, scale-dependent responses to vegetation cover are identified by taking a

multi-scaled approach. These findings are of considerable practical importance for gaining

insights into which species respond to different scales of protection in existing areas of native

1 / INTRODUCTION 23

vegetation, efforts to increase the amount of native vegetation over time, and both approaches

together.

Variation in bird biodiversity at landscape, farm, and site scales exhibited significant

intrinsic scale-specific effects. This dependence was largely accounted for by native vegetation

cover with aggregate biodiversity increasing with increasing native vegetation cover at each

spatial scale and over time. Absolute gains in biodiversity per unit increase in vegetation cover

were greatest at relatively low amounts of vegetation cover. Every doubling of percent cover

resulted in an increase of 3.1, 2.3, and 0.7 species per landscape, farm, and site respectively.

These results can help prioritise investment strategies such as replanting native vegetation under

agri-environment schemes.

Cross-sectional relationships were identified with the amount of vegetation cover. These

were typically positive for woodland birds and negative for open-country birds. However, for

some species the relationships differed between spatial scales, suggesting differences in nesting

and foraging requirements. There was a 3.5% increase in the amount of native vegetation cover

in the study region between 2002 and 2010, and analyses revealed that some open-country

species responded negatively to these temporal changes, typically at the farm and/or site scale,

but not the landscape scale. Species generally exhibited stronger cross-sectional relationships

between occupancy and the amount of vegetation cover than between changes in occupancy and

changes in vegetation cover. This unexpected result could be attributed to differences in habitat

use by birds of existing vegetation cover (typically old growth woodland) versus plantings and

natural regeneration, the main contributors to temporal increases in vegetation cover.

In document Design and analysis of quasi-experiments in landscape ecology: responses of fauna to landscape vegetation transformation in South-Eastern NSW (Page 30-33)