Biological communities are changing across the globe as a result of anthropogenic
pressures; abundances of individuals are declining within populations and species
are becoming extinct. Biological diversity and trophic complexity in grasslands
and soil food webs are positively associated with the cycling of nutrients in soil and
water, primary productivity and decomposition. Since these ecosystem processes
underpin a number of goods and services to society, human-driven changes in the
structure of ecosystems could negatively impact upon human wellbeing. However,
the majority of our knowledge of the role of biodiversity in ecosystem functioning
comes from studies conducted in temperate grassland systems. Consequently, our
understanding of how of higher-level organisms influence ecological processes in
different ecosystems is limited. This thesis aims to address these knowledge gaps
by investigating how dung beetle traits and functional diversity influence the secondary
dispersal of seeds and the emergence and survival of seedlings in the
northeastern Brazilian Amazon. My first research aim was to understand the importance of intraspecific variability
in dung beetle traits for the accuracy of functional diversity (FD) indices (Chapter
2). This chapter demonstrates that intraspecific differences in dung beetle traits
are small compared to between species differences. However, failure to include intraspecific
variability resulted in large errors in the calculation of FD indices when
describing small and/or species poor communities. Second, I investigated how
dung beetle diversity influences secondary seed dispersal, and the role of environmental
context in modulating relationships. Here I reveal positive relationships
between dung beetle functional diversity and both the probability of seed
burial and the dispersion of seeds throughout the soil profile. However, these patterns
were dependant on soil type and thus environmental context (Chapter 3). Finally,
I explored the multitrophic significance of findings from Chapter 3 by testing
how dung beetle communities affect the burial of different sizes of seeds and
emergence and survival of seedlings (Chapter 4). Results from this chapter demonstrate how dung beetles could influence vegetation regeneration because
beetle diversity negatively affected the likelihood that experimental seeds emerged
from the soil surface, but positively impacted on the likelihood that emerged seeds
survived until the end of the experiment period. Furthermore, I show that large
seeds could be more vulnerable to anthropogenic driven changes in dung beetle
communities than smaller seeds. These research aims were realised through field-based experiments from which I
sampled and identified approximately 2,650 dung beetles from 180 naturally
formed communities, collected more than 17,000 morphological trait measurements
and sieved approximately 11 tonnes of soil in search of 1800 seed mimics.
Overall, this work demonstrates diversity in dung beetle communities is positively
associated with the ecological processes they govern but that environmental context
is instrumental in modulating biodiversity-ecosystem functioning relationships.
I use the outcomes from this work to discuss the challenges in describing
diversity-functioning relationships across trophic levels. Finally, I highlight that
ecological processes are the product of complex species-specific interactions, dependent
on the biotic and abiotic environment. Therefore, predicting the consequences
of anthropogenic-driven species losses for the structure and functioning
of natural systems is a major research challenge.