Download Patterns and maintenance of biodiversity

Patterns and maintenance of biodiversity
(M. Wikelski and B. Kempenaers)
Contents
1 At a glance
2 Definition of topic
3 Status of the field
4 Key scientific questions and opportunities
5 Research opportunities, needs and challenges
6 Expected outcome and benefits
7 References
8 Figures
1 At a glance
In this period of rapid global change, biodiversity is under unprecedented threat
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, yet many critical
questions regarding its evolution, function and geographic distribution remain unresolved.
•
Understanding biodiversity, the coexistence of many different life forms, is thus one of the
most urgent and challenging topics in biology3. Higher diversity increases productivity,
presumably through increased efficiency of more specialized individuals. Changes in
biodiversity can have dramatic effects on human health, ecosystem functioning and the
stability of ecosystem services4,5. Current climate change and human alteration of
landscapes influence biodiversity in many unforeseen ways6.
•
Studying patterns and processes of vertebrate biodiversity in nature allows for experimental
scientific approaches using a variety of techniques, including state-of-the-art bio-logging7.
Exemplary results gained from these studies will highlight the mechanisms underlying the
maintenance of diversity in all life forms and be at least partly generalizable to other study
systems8.
2 Definition of topic
The various meanings of biodiversity are almost as diverse as the name itself implies. Anything
biological is diverse9. Here we concentrate on two aspects of biodiversity that are heuristically
tractable and amenable to experimental studies: i) the diversity of vertebrate species, particularly
birds, and ii) the diversity of life history traits among those species. Both aspects need to be studied
in the wild under the constraints where organisms evolved. Understanding species diversity requires
us to predict why certain species only occur in specific areas at specific times. Understanding global
diversity in life history traits implies knowledge about selective forces that favour certain traits or
combination of traits depending on ecological factors, including local species composition .
3 Status of the field
A general and comparable species concept as well as phylogenies exist for higher vertebrates,
particularly birds, and allow us now to map their entire, global diversity as well as population
densities, and life-history traits such as survival and fecundity in space and time (Fig. 1). Such
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detailed knowledge is unique to this group of life forms and based upon, and grounded in, centuries
of natural history and ecological studies.
Among and within vertebrate species, life histories differ vastly (Fig. 1b), generally along a slowto-fast continuum representing the speed of life exemplified by energy turnover or reproductive
rates. Differences in life histories can be mapped upon morphological and physiological traits and
from there to genetic traits, up to gene expression10 (see also chapter by Weigel & Tautz, this
volume). Thus the study of vertebrate biodiversity allows for the link between, and the mechanistic
scaling from, genes to individuals to life histories and further to species diversity and ecosystem
complexity.
4 Key scientific questions and opportunities
Fundamental biodiversity questions are:
a) Why does an individual live here but not there? Answering this question first and foremost
requires knowledge of the global pattern of species occurrences (Fig. 1a). Furthermore, an answer
involves a deep mechanistic understanding of physiological, behavioral and ecological relationships
of each individual with its abiotic and biotic environment. We also need to know the biogeographic
and phylogenetic history of a species assemblage, as well as the movement ecology of the species
involved. Knowing the answers to this question will tell us why certain organisms are restricted to
small areas whereas others are cosmopolitans. We will also understand why some species or
individuals are good, others bad invadors into new habitats, and why some species are better able to
cope with environmental change than others.
b) How many individuals of which type can coexist locally? To answer this question we need to
know the type and strength of interactions between organisms. Who is cooperating with whom, who
excludes whom, who is a key species in an environment? We also have to understand how
individuals are packed into ecological space (i.e., their ‘ecological niche’) and how the environment
is split up between individuals. We will learn how individuals partition their niches and how
different individuals or species exploit their environment.
c) How flexible are the assembly rules of biodiversity? The ongoing environmental changes provide
exciting research opportunities challenging species assembly rules by altering both abiotic and
biotic factors and interactions. Understanding this question will thus allow us to predict whether
changes in biodiversity will be gradual or discontinuous. We need to know the answer to these
questions because agriculture, human health and ecosystem health depend upon a functional
assembly of organisms. Once a species assemblage is modified beyond repair, it can not provide the
ecosystem services humans have grown used to.
d) How can high biodiversity and associated high productivity be restored? Once an ecosystem is
degraded, biodiversity is usually vastly diminished. The vegetation cover of many areas around the
world is currently altered to a spatial extent that makes a quick recovery of habitats and associated
animal biodiversity difficult. Once we understand species assembly rules that enhance biodiversity
over time, we will be in a situation to bio-engineer rapid recoveries of habitats – if not to their
original state, at least to their quasi-original functionality in terms of ecosystem services. Such renaturation systems provide ample and welcome study opportunities for experimental tests of our
scientific understanding of the patterns and mechanisms enhancing biodiversity.
5 Research opportunities, needs and challenges
Studying patterns and mechanisms of biodiversity can benefit strongly from focusing on tractable
research systems. We narrowly restrict our approach to higher vertebrates, particularly birds (class:
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Aves), a highly speciose vertebrate taxon (~9800 species). This provides a unique opportunity to
gain knowledge on a global scale about the evolution and maintenance of biodiversity and of lifehistory traits11. First, birds display a phenomenal diversity in terms of body sizes, foraging habits,
longevity, migration, sociality, fecundity, sexual dimorphism, mating strategies, parental care
behavior, coloration, song and breeding displays, and many other traits. Second, there are vast
stores of data on avian natural history, morphology, demography and geographic ranges collected
through decades of dedicated research by a huge number of amateur and professional ornithologists.
Third, because birds are conspicuous and abundant high trophic feeders, and because global
patterns of species richness are highly correlated among amphibians, reptiles, birds and mammals12,
they serve as key indicators for health of the environment8. Birds offer the most cost-effective
system towards understanding global loss of biodiversity, biodiversity hotspots and the effects of
climate change on ecological systems. In birds we can directly and experimentally study:
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What are the evolutionary and ecological causes of the dramatic latitudinal variation in the
diversity of species and their traits?
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What drives the dramatic cross-species and geographic variation in the diversity of life
histories, metabolic strategies, mating systems, behaviors and their respective physiological,
neural and genetic underpinning?
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How strong is the environmental control of the spatial distribution of biodiversity and its
many attributes, and how is each likely to respond to the anticipated perturbations of
climatic gradients under global change?
More specifically, we can initially narrow our research focus to the following projects:
(1) Describe the existing variation in avian global life-histories by accumulating published data on
avian biodiversity in terms of habitat, longevity, diet, developmental processes, morphology,
migration patterns, nesting ecology, detailed parental care behavior, mating strategies, plumage
coloration, display behavior and song. The resulting database can be made available to the scientific
community.
(2) Understand the factors that lead to increased or decreased diversity in avian life-histories at both
a community and global scale. Species that occur in biodiversity hotspots (such as rain forests) have
different suites of life-history traits than species in less biodiverse locals (such as the arctic). For
example, we do not know why high species richness appears to come hand in hand with higher
longevity, delayed ages of first breeding, and smaller clutches. What is the relationship between
life-history diversity and species diversity (in terms of species richness)?
(3) Use the changes in avian life-history patterns over time as a quasi-experimental natural study
system. In particular, study how avian life-history traits will influence success or failure towards
different species adapting to global environmental change. What life-history strategies will predispose birds to adapt to global climate change and how will avian life history traits change in
coming years? What is the importance of phenotypic plasticity and additive genetic variation?
Climate change is expected to result in major evolutionary changes in birds. Through detailed
temporal information on changes in avian demography and distributions, in combination with lifehistory information, we will be able to isolate the particular life history traits (down to genomic
adaptations) favored under climate change. This will help us identify the kinds of species at most
risk in the face of global environmental upheaval.
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(4) Map distributional changes over time onto individual movement data using the nascent global
‘Movebank’ database (http://www.movebank.org). Here we can rely upon the breakthrough new
technology of bio-logging, i.e., the continuous surveillance of individual behavior using ‘black-box’
data loggers on animals7. Such loggers can now record a multitude of physiological parameters and
thus allow us to link internal (e.g., heart rate, EEG) and external parameters (e.g., temperature,
wind, other animals). The heuristic value of black-box bio-loggers can not be overemphasized.
(5) Link global variation in current ornithological knowledge with conservation needs. There is a
clear geographical signature on the amount of information that is available about birds. A global
“knowledge map” of birds can be made based on the availability of information on some basic traits
per species (Fig. 2). This map highlights areas where gaps in our information about species are most
apparent. Not surprisingly, westernized areas of Europe, North America and Australasia comprise
locations where we know the most. African avifauna is also particularly well known, due to a long
history of ornithological research throughout the continent. Of great importance is that areas with
equatorial regions with the highest biodiversity are also the areas most poorly understood in terms
of basic ornithological information. These results provide a critical empirical insight towards
biodiversity conservation: the areas we need to preserve the most are the areas we understand the
least. The map highlights clear target areas where future research into basic avian biology is needed
most.
6 Expected outcome and benefits
Once we gain an exemplary understanding of the patterns and processes involved in the evolution
and maintenance of biodiversity in birds, we are prepared to generalize towards other study
systems13. Biodiversity science will thus have immediate benefits to humans: we will be able to
predict how agricultural biodiversity begets productivity, thus enhancing crop output around the
world. We will predict where, when and by whom biological invasions most likely occur, reducing
the costs of the annual multi-billion dollar fight against invadors significantly. We will be able to
use biological agents as ecosystem engineers, for example for seed dispersal in highly fragmented
landscapes, or in agricultural pollination systems by supplementing honey bees with native bees.
Bio-prospectors searching for drug components will be directed to areas where biodiversity
researchers predict high inter-specific competition and associated use of defensive secondary
compounds by plants and animals. Biodiversity knowledge is also expected to calm public concerns
about the perceived dangers of genetically engineered organisms. Once we understand the patterns
of species interactions and can predict community structures and the niche partitioning among
species, we will be able to predict any residual potential for harm done by organisms with new
physiological or life history traits. The importance of a better understanding of species and their
ecology can hardly be overstated14.
7 References
1) Araujo, M. B. and C. Rahbek (2006). How does climate change affect biodiversity? Science
313(5792): 1396-1397.
2) Myers, N., R. A. Mittermeier, et al. (2000). Biodiversity hotspots for conservation priorities.
Nature 403(6772): 853-858.
3) Carpenter, S. R., R. DeFries, et al. (2006). Millennium Ecosystem Assessment: Research needs.
Science 314(5797): 257-258.
4) Kleijn, D., R. A. Baquero, et al. (2006). Mixed biodiversity benefits of agri-environment schemes
in five European countries. Ecology Letters 9(3): 243-254.
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5) Hooper, D.U., F. S. Chapin, et al. (2005). Effects of biodiversity on ecosystem functioning: A
consensus of current knowledge. Ecological Monographs 75(1): 3-35.
6) Sala, O. E., F. S. Chapin, et al. (2000). Biodiversity - Global biodiversity scenarios for the year
2100. Science 287(5459): 1770-1774.
7) Cooke, S. J., Hinch, S. G., Wikelski, M., Andrews, R. D., Kuchel, L. J., Wolcott, T. G., Butler, P.
J. (2004). Biotelemetry: a mechanistic approach to ecology. Trends in Ecology & Evolution 19(6):
334-343.
8) Furness, R.W. 1993. Birds as monitors of environmental change. Chapman & Hall.
9) Gaston, K.J. 2000. Global Patterns in biodiversity. Nature 405, 220-227.
10) Abzhanov, A., M. Protas, et al. (2004). Bmp4 and morphological variation of beaks in Darwin's
finches. Science 305(5689): 1462-1465.
11) Jetz, W. & Rahbek, C. 2002. Geographic range size and determinants of avian species richness.
Science 297: 1548-1551.
12) Lamoreux, J. F., et al. 2006. Global tests of biodiversity concordance and the importance of
endemism. Nature 440: 212-214.
13) Schroter, D., W. Cramer, et al. (2005). Ecosystem service supply and vulnerability to global
change in Europe. Science 310(5752): 1333-1337.
14) May, R. M. & Harvey, P. H. (2009). Species Uncertainties. Science 323: 687 (Editorial).
8 Figures
Figure 1
Fig. 1a:
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Fig. 1b:
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Fig. 1c:
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Fig. 1d:
Fig. 1: Global species richness of all birds (a), proportion of songbirds (Passerine) species that are
cooperative breeders (b), mean clutch size of bird assemblages (c), minimum temperature change
between 2000 and 2090 predicted across the geographic ranges of bird species in an assemblage (d)
(CCSM3, A2 scenario; expressed in units standard deviation of current-day conditions across
range). Source: Walter Jetz lab, Yale University.
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Figure 2
Fig. 2: Global pattern of knowledge about birds. We determined for each species the proportion of
four natural history characteristics for which information for that species is available (sexual size
dimorphism in wing length, clutch size, parental care behaviour, and species body mass). For each
grid cell we show the mean proportion of known traits for the community of species present in that
cell (Dale J, Valcu M & Kempenaers B, manuscript).
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