Transcript Indirect Effects in

UNIVERSITY OF NOVA GORICA
SCHOOL OF ENVIRONMENTAL SCIENCES
Indirect Effects in Ecology
Irena KRANJC
Menthor: Marko Debeljak
Ljubljana, 2015
Interrelations among ecosystem components and processes can be
subdivided into direct and indirect effects:

Direct effect - restricted to the direct effect of one component (or
process) on another, and are attributable to an explicit direct
transaction of energy and/or matter between the components in
question)

Indirect effect - those which are not comply with the above restriction
2

In nineteenth century the significance of indirect interactions
was well realized and was accounted for in the classic studies
of Darwin, Dokuchaiev, Gumboldt, Engels, and many other
scientists.

In the twentieth century, appreciation of indirect effects in
nature received considerable acceleration, due to:



accumulating interdisciplinary knowledge of natural ecosystems,
development of appropriate mathematical techniques,
urgent necessity to resolve the growing problems of environmental
damage, resulting from the uncurbed expansion of the human
population backed by the advances of the technological progress.
3

Popularization of Vernadsky’s fundamental theories about
the ‘biosphere’, the ‘noo¨sphere’, and interrelations between
biota and geochemical cycling stimulated investigations of
indirect effects even more.

Among a lot of possible indirect effects, there are five that
have been most commonly studied:





Interspecific competition
Apparent competition
Trophic cascades
Indirect mutualism and commensalism
Interaction modification
4
Interspecific competition
– two
species (or several)
compete for the same resource. An increase in Component 1 will
lead to the increased consumption of the shared resource
(Component 2), and consequently to the decrease in a competitor
(Component 3)


two predators sharing the same prey
two microbial species whose growth is limited by the availability of
the same nutrient
indirect effect
1
3
2

Figure 1:Interspecific competition
5
Apperent competition – two species have a common
predator

an abundant population of species 1 sustains a high density
population of predator 2, who, in turn, may limit the population of
another prey species 3.
Indirect effect

indirect effect

2
1

3
Figure 2: Apperent competition
6
Trophic cascades – Trophic cascades involve propagation of
the effect along a vertical trophic chain consisting of three or
more components connected by grazing or predation.

an increase/decrease in Component 4 will lead to the
decrease/increase in Component 3, increase/decrease in Component 2,
and decrease/increase in Component 1.

These effects are particularly well studied in aquatic food chains,
terrestrial systems
7
Indirect mutualism and commensalism
– Indirect
mutualism and commensalism involve a consumer – resource
interaction coupled with either exploitative or interference
competition.

Starfish and snails reduce the abundance of mussels, a dominant
space occupier and increase the abundance of inferior sessile species.

The presence of grazers on oyster farms in Australia increases oyster
recruitment by removing algae, who otherwise preempt the available
spaces. An increase in species 1 should lead to a decrease in species 2
and an increase in species 3.
8
Interaction modification
– the relationship between a
species pair is modified by a third species

Interaction modification’is often, and quite rightly,
considered as a principally different type of indirect effect.
By coupling interaction modifications with other types of
relationships (e.g.,trophic), one may arrive at possibilities of
numerous relationships. One of the more simple of such
combinations may be exemplified with an indirect effect of
grazers and certain agricultural practices on the population
density of foxes and the rodent in Eastern Europe (V.
Takarsky, personal communication)
9

Lower grazing rates lead to a denser and taller grass cover,
enabling more successful hunting of predators.

Conversely, higher grazing rates lead to a lower grass cover,
thus enhancing the detection of predators by the rodents. As a
result, increase in grazing may have an indirect positive effect
on the rodent population and an indirect negative effect on the
population of foxes

Figure 4: Predators and Rodents
10
Classifications of Indirect Effects
Indirect effects can be characterized in a number of ways and
may conveniently contribute to the toolbox for comparative
ecosystem analysis:






related to the characteristics of exerting, receiving, and
transmitting compartments
presence/absence of a lag phase before the manifestation of a
response,
strength of the interaction (particularly in relation to the direct
interactions) and its directionality (e.g., whether it is isotropic or
anisotropic),
dependence on a specific ecosystem context,
importance for the functioning of the compartments involved,
importance for structural (e.g., successional or evolutionary) changes
in the populations involved and the whole biological community, and
significance for overall ecosystem functioning.
11
Indirect Effects
All the relations not restricted to the effects of a direct transaction
of matter and energy between the adjacent ecosystem
components are treated as indirect.
12
Examples of Occurrence and Importance of Indirect
Effects






Indirect Effects in Terrestrial Environment
Indirect Effects in Aquatic Systems
Role of Abiotic Components
Indirect Effects of Global Relevance
Indirect Effects and Industrial Ecology
Evolutionary Role of Indirect Effects
13
Indirect Effects in Terrestrial Environment
In the end of nineteenth century the school of thought founded by
Dokuchaiev had developed a theory that soil was a product of
complex interactions between climate and geological and
biological components of the terrestrial landscape.
Indirect effects in terrestrial ecosystems relate to the dependence
of plant nutrient supply on mineralization of nutrients by soil
biota, and to the propagation of these effects through the food
chain.
Soil fauna may help to disperse microorganisms crucial for plant
functioning and biogeochemical cycling, and physically modify
the habitat, thus changing environmental conditions for all the
biological community. Plants, in turn, modify the habitat for
other organisms, for example, by producing litter, providing
shade, shelter, etc.
14
Indirect Effects in Aquatic Systems
Recent studies of indirect effects in aquatic environment
variously involved a combination of the empirical approach and
an application of statistical techniques, methods of network
analysis, simulation modeling using ‘What if’ scenarios, and
sensitivity analysis.
One of the perhaps most frequently addressed examples of
indirect effects in aquatic environment relate to trophic cascades,
which involve propagation of the effect along a vertical trophic
chain consisting of three or more components connected by
grazing or predation. Daskalov was recently investigated a
decrease in the top predator’s population in the Black Sea due to
overfishing resulted in a ‘trophic casade’, leading to an increase
in the abundance of planktivorous fish, a decline in zooplankton
biomass, and an increase in phytoplankton crop.
15
Role of Abiotic Components

In ecology, it is widely recognized that species interaction can
be mediated by a nonliving resource, and that a species can
potentially exert a selective force on another species through
nontrophic interactions. It should also be noted that in nature
many species are very well adapted to modify their
community and habitat.



beavers by changing the habitat’s hydrological regime,
humans by initiating dramatic changes in global climate and
geochemical fluxes,
earthworms by increasing aeration and redistributing organic matter
in soil
16
Indirect Effects of Global Relevance


Indirect relationships important on the global or sub global
scale are often separated from their cause spatially and/or
temporally.
For example, the dramatic increase in volcanic activity
(possibly caused by the impact of an asteroid) at the end of
the Mesozoic era is thought to have led to the extinction of
dinosaurs, which arguably stimulated the eventual evolution
of mammals (including humans).
Figure 5 : Volcanic activity
17

The increased production and use of fertilizers in the 1950s
led to the increased phosphate inputs, eutrophication, and
decrease in water quality in many lakes, ponds, and reservoirs
during the subsequent decades.
Figure 6: Water pollution
18

The increased consumption of fossil fuels in the twentieth
century led to the increased emissions of carbon dioxide,
which were eventually followed by global warming and an
apparent increase in the frequency of natural disasters.

Global climate change (principally related to the increased
concentrations of greenhouse gases) is still one of the most
discussed topics in ecology and environmental sciences in
general.
Figure 7: Effects of Global Warming
19
Indirect Effects and Industrial Ecology

Industrial ecology is based on the analogy between natural
and industrial ecosystems, and aims to facilitate the
development of industrial recycling and cascading
cooperative systems by minimizing the energy consumption,
generation of wastes, emissions, and input of raw materials.

One of the commonly used methods of industrial ecology is
‘life cycle assessment’ (LCA). It studies the environmental
aspects and potential impacts throughout a product’s life
("cradle to grave"), from raw material acquisition through
production, use and disposal.
20

Similar to LCA, but usually with considerably narrower
system boundaries, are methods of energy analysis, including
energy footprinting (which, effectively, constitutes
calculations of how much energy is spent and saved
/recovered in all the processes included within the chosen
system boundary) and net energy analysis (which in addition
to the detailed energy budgeting involves calculation of
indicators such as incremental energy ratio and absolute
energy ratio).
21

Another method popular in ‘industrial ecology’ is ‘ecological
footprinting’. The method estimates the area necessary to
support (i.e., in terms of, for example, production of food,
energy, processing of wastes) current, past, or probable future
functioning of particular geographical units.

Only the ecofootprints of Australia and Canada appear to fit
inside their borders. The rest of the ‘developed’ countries
appear to live on the expense of other territories.
22
Evolutionary Role of Indirect Effects

Indirect effects often promote coexistence and the role of
indirect effects should, in general, increase in the course of
evolution.



In grassland communities containing Rumex spp., insect herbivory
(by Gastrophysa viridula) appears to be a cost inherent in the
development of plants resistance to pathogenic fungi (Uromyces
rumicus).
infection of plants with endophytic fungi often enhances plants
competitive abilities via deterring grazers by production of toxic
compounds (as a result, some plants might have coevolved together
with their endophytes)
It should be noted, that indirect effects are important for the
evolution of not only natural, but also industrial ecosystems.
23
Approaches and Techniques Used to Detect and
Measure Indirect Effects

Detection and measurements of indirect effects are often far
from straightforward, and are mostly based on the intuition,
common sense, and prior knowledge of any particular system.

Abrams and co authors described two major approaches
adopted in ecological studies:



Theoretical
Experimental
Some ecologist think that the methodological continuum to
study indirect interactions is best represented by a triangle
with observational, experimental, and theoretical nodes.
24
Theoretical approach - observations (and/or carefully considered
experimental data) are used together with theoretical
considerations to construct a model capable of investigating
interactions among the components incorporated in the model
structure.
Experimental approach - densities of individual species are
manipulated (e.g., by total removal) in microcosms or
experimental plots, and statistical analysis (e.g., ANOVA,
ANCOVA) are subsequently applied to estimate the magnitude of
indirect effects of manipulations on densities of other species.
Mathematical methods which have been used in studies of
indirect effects in natural ecosystems are statistical methods
(PCA, factor analysis, CCA, ANCOVA, ANOVA), simulation
modeling (e.g., using ‘what if scenarios’, sensitivity and elasticity
analysis), and methods of network analysis.
25
Problems and Implications for Environmental
Management

There are many problems associated with studies of indirect
effects.




Complexity and Uncertainty
Separation in Time
Separation in Space
Defining System Boundaries
26
Implications for Environmental Management

Qualitative and quantitative account of indirect effects is
becoming a common part of environmental management, and
is indispensable for successful application of landscape
engineering, biomanipulation, biogeochemical manipulation,
strategic environmental assessment (SEA), and environmental
impact assessment (EIA), etc. In particular, mathematical
methods can be helpful in this respect.

A combination of empirical and theoretical work should
precede any practical steps, and any desk study should be
backed up by a thorough monitoring plus experimental
program.
27
Current and Further Directions

Further investigations of indirect effects are
important both for enhancing our understanding and
therefore improving management of specific
ecosystems, and for general development of ecology.
28
Questions
1.How can we subdivided interrelations among
ecosystem components and processes?
2. Which are five most commonly studied
indirect effects?
3. List three examples of Importance of Indirect
Effects
4. What kind of Approaches and Techniques we
Use to Detect and Measure Indirect Effects?
29