Spatial Ecology: Patterns and Processes

145 Pages·2013·6.917 MB·English

by  Vikas Rai

Spatial Ecology: Patterns and Processes
Authored by
Vikas Rai
Guest Scientist
School of Environmental Sciences
Jawaharlal Nehru University
New Delhi
India
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CONTENTS
Foreword i
Preface iii
CHAPTERS
1) Introduction 3
2) Basic Interactions: Processes in Time 10
3) Ecosystems in the ‘Bottle’: Microcosm Experiments 28
4) Principles of Ecological Dynamics 48
5) Role of Space 65
6) Dynamics and Patterns 93
7) Issues in Spatial Ecology 122
Index 135
i
FOREWORD

Spatial dynamics is one of the most active and important fields in ecology, just
like it was when I started graduate school over 35 years ago. Visiting Simon
Levin’s lab, I saw him give a seminar about his now-classic work with Robert
Paine on spatial patterns in rocky intertidal communities, in which the age-
structured McKendrick-von Foerster equation was inventively transformed into a
model for the spatiotemporal dynamics of disturbance-renewed patches of
mussels and barnacles. It exemplified the power of mathematics to illuminate the
natural world, and who could want any other career? At some point Vikas Rai
must have had the same kind of epiphany, and this eBook is one of the results.

But now, after many decades of research in spatial ecology, why isn’t everything
solved? Why do we need this new eBook, instead of finding everything in old
eBooks on the library shelf? The complexities of spatial dynamics in ecology may
be more than we can ever fully understand, but our understanding continues to
increase. New genomic tools give us information about rates of dispersal among
sub-populations. Long-term population monitoring data tell us that species really
do spread as travelling waves (at least sometimes), and reveal interesting new
twists such as the interplay between ecological and evolutionary dynamics in the
spread of the cane toad. New methods in computational statistics let us fit realistic
spatial models to data, and challenge ourselves to quantitatively understand the
colonization-extinction dynamics of local populations. The spatial dynamics of
pathogens and immune system cells within individual organisms turns to be
important for understanding infectious disease outbreaks. New data demand new
theory. And old puzzles, such as Hutchinson’s Paradox of the Plankton, also
challenge us still to develop new theories.

Understanding the world is only part of the ecologist’s job. Increasingly,
ecological knowledge is required to manage and preserve it (should the fossil fuel
industry allow us the opportunity). Our era has been called the Homogocene by
some: the era in which species spread globally, invading and spreading through
new habitats. I live in a landscape defined by lakes, the Finger Lakes region in
New York, and recent invasions by mussel species and invasive plants have
ii
caused profound changes in many of the lakes. It’s also a farming region, divided
into patches with very different ecological characters (forest, riparian, vineyard,
corn field, dairy farm, etc.). Every population is a metapopulation here, and just
about everywhere else in the human-dominated world, both the populations we
want to preserve and those we want to eliminate.
But understanding spatial ecology has to start with understanding local ecology,
so it’s right that this eBook only gets to spatial ecology in Chapter 5, after
preceding chapters have laid the foundations. From there it could go on almost
forever, because of the way spatial concerns have spread throughout ecology, but
it doesn’t. It’s not an encyclopedia, it’s a very personal eBook telling you what
one student of nature thinks is most important in spatial ecology. Reading this
eBook will earn you a “driver’s license” for continued explorations in spatial
ecology, and a first look at some of the interesting features of a vast landscape
that you can explore on your own. And if it captures your imagination, you can
rest assured that there will be plenty of useful work to do for the rest of your
career.
Stephen P. Ellner
Department of Ecology and Evolutionary Biology
Cornell University
USA
iii
PREFACE
Well–mixed models (WMM) have served ecological science to represent
“microcosm” experiments. Application of non–linear dynamics to the analysis of
WMMs revealed that these models are useful to clarify the essential dynamics of
ecological systems represented by these microcosms. Since there exist several
processes in ecological systems which are spatial in nature (e.g., random and
directed movements of animals and plants), study of the role of space in
ecological dynamics must be studied. The present eBook elucidates demerits of
WMMs and throws light on how role of space can be incorporated in
mathematical models of ecological systems.
Anthropogenic causes have affected Climate Change. Three main components
of climate change at global scale are Fossil Fuel Combustion, 2) Nitrogen Cycle,
and 3) Land Use/Land Cover Change. Under background conditions, biological
nitrogen fixation in terrestrial ecosystems has been estimated at 100Tg (1 Tg =
102g) of Nitrogen per year globally (Soderlund and Rosswall 1982); nitrogen
fixation in marine ecosystems adds 5–20 Tg more (Carpenter & Capone 1983),
while fixation by lightning accounts for 10 Tg or less (Soderlund & Rosswall
1982). In contrast to this natural background, industrial nitrogen fixation for
nitrogen fertilizer now amounts to > 80 Tg per year. An additional 25 Tg of
Nitrogen are fixed by internal combustion engines and released as oxides of
nitrogen, and 30Tg are fixed by legume crops. The global Nitrogen cycle has
now reached the point where more Nitrogen is fixed annually by human–driven
than by natural processes. Bazzaz and collaborators (1994) recognized early the
ecological implications of increasing Carbon Dioxide concentrations. Elevated
carbon dioxide increases photosynthetic rates of most plants with the C
3
photosynthetic pathway in the absence of other limiting resources. It increases
both photosynthetic water use efficiency and integrated nutrient use efficiency
and is so developed that it is well equipped to handle.
Stability of an ecological system is a property which provides us an idea of the
behaviour of the system when acted upon by small perturbations. Another closely
related quantity is engineering resilience which is defined as the time taken by
iv
the system to return to its original state. Spruce budworm forest community
presents an example of a system with low stability and high resilience. In regions,
which witness benign climatic variations, populations are not able to withstand
climatic extremes even though the populations tend to be constant. This
exemplifies a situation of high degree of stability. Ecological resilience resides
both in the diversity of the drivers and number of passengers who are potential
drivers. Walker (1995) has shown how the diversity of functional groups
maintains the ecological resilience. The research on discontinuities in ecological
systems suggests the presence of adaptive cycles across the scales of a panarchy;
a nested set of adaptive cycles operating at discrete levels (Gunderson & Holling
2001). A system’s resilience depends on the interconnections between structure
and dynamics at multiple scales. Complex systems are more resilient when the
threshold between a given dynamic regime and an alternate regime is higher (Ives
& Carpenter 2007).
The eBook presents developments in mathematical theory which is relevant to
study the effect of changes in habitat, soil and air quality.
ACKNOWLEDGEMENTS
The author is grateful to Prof. M. I. Ali Ageel for providing less teaching
workload. Ranjit Kumar Upadhyay and Stephen Ellner are thanked for helpful
discussions.
CONFLICT OF INTEREST
The author(s) confirm that this chapter content has no conflict of interest.
Vikas Rai
Jawaharlal Nehru University
India
E-mail: [email protected]
REFERENCES
Bazzaz, FA, Miao, SL & Wayne, PM (1994) CO2–induced enhancements of co-occurring tree
species decline at different rates. Oecologia, 96, 478–482.
v
Carpenter, EJ & Capone, DG (1983) Nitrogen fixation by marine Oscillatoria Trichodesmium in
the world’s oceans. Pages 65–103 in Carpenter, EJ & Capone, DJ, eds. Nitogen in the
marine environment. Academic Press,New York, USA.
Gunderson, L & Holling, CS (2001) Panarchy: Understanding transformations in systems of
humans and nature (eds). Inland Press, Washington, DC,USA.
Ives, AR & Carpenter, SR (2007) Stability and diversity of ecosystems. Science, 317, 58–62.
Soderlund, R & Rosswall, TH (1982) The nitrogen cycles. Pages 62–68 in O. Hutzinger, editor.
Handbook of Environmental Chemistry, Springer–Verlag, Berlin.
Walker, B (1995) Conserving biological diversity through ecosystem resilience. Conservation
Biology, 9, 747–752.
Send Orders of Reprints at [email protected]
Spatial Ecology: Patterns and Processes, 2013, 3-9 3
CHAPTER 1
Introduction
Abstract: Mathematical modelers hardly have sound knowledge of biological systems
they intend to explore. Therefore, it is essential to introduce key concepts; e.g.,
populations, species, communities, etc. It presents a description of how diversity of
species is organized in different taxonomic classes. All relevant phenomena which play
important role in spatial systems are discussed. Allee effect is a phenomenon which
governs the rate of growth of a population at low population densities. At higher
population densities, growth of a population is limited by its carrying capacity. Habitat
fragmentation and Allee effect are two key factors which determine the population
growth and community structure. The chapter identifies challenges for a mathematical
modeler in the present day scenario and indicates how these challenges could be
handled in future. It also describes how the eBook is organized.
Keywords: Populations, Communities, Species, Diversity, Speciation, Allee
effect, Habitat fragmentation, drivers, passengers, Keystone species, competitors,
Population growth, Malthusian model, Verhulst model, Predator–Prey systems,
Homogeneous environment, Non–spatial models, Differential equations,
Heterogeneous environment, Climate change.
OVERVIEW
In order to appreciate diversity of life forms, species have been arranged into
different phyla; e.g., Arthropods, Arachnids and relatives (Chelicerata). Crabs,
shrimps, spiders, millipedes, centipedes and insects are well known arthropods.
Over 85 per cent of total species in the biosphere belongs to this phylum. There
are nearly 1 million species of insects. For example, Thrips are minute narrow
insects with elongate, fringed wings and rasping–sucking mouthparts. Mostly
sap–sucking elements on plants, a few of them are capable of penetrating the skin
and sucking blood; e.g., Karnyothrips flavipes, a predator of scale insects in the
Mediterranean sub-region. These insects cause etching and rashes through skin
pricking, or inflammation in the eyes, ears and throat. This usually happens when
their food plants dry up under adverse climatic conditions. Blood sucking moth
are of two types: 1) those which pierce the skin and suck blood and 2) those
which scrape the skin and suck blood. The noctuid Calyptra eustrigata belongs to
the former group with strong proboscis which enables it to pierce the skin of a
Vikas Rai
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