Impact of Lake Organisms on Terrestrial Systems

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Impact of Lake Organisms on Terrestrial Systems

• By Vik Walia

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Outline

• 1. Introduction
• 2. Article 1 Trophic Cascades
• 3. Article 2 Indirect Effects of Aquatic
  Insects on Terrestrial Insects
• 4. Future Directions

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Introduction

• So What are trophic cascades anyways?
• - Interactions between trophic levels
  (decomposer, producer, herbivore, predator) that
  result in inverse patterns in abundance or
  biomass across more than one trophic link in a
  food web

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Example Consider a 3-level food chain

• Predators can decrease herbivore
  abundance/biomass, indirectly benefiting the
  plants (the producers)

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Article 1 Trophic Cascades Across Ecosystems

• Purpose Show that Fish indirectly facilitate
  terrestrial plant reproduction through cascading
  trophic interactions across ecosystem boundaries

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4 Aspects were tested to prove hypothesis

• Fish limit the size and abundance of larval
  odonates
• Correlation of fish presence with pollinator
  visitation
• Whether effects of fish indirectly influenced
  plant reproductive output
• Pollinator visitation would be lower near
  fish-free ponds for 2 reasons
• Adult dragonflies predate on pollinators
• Pollinators behaviourally avoid foraging near
  adult dragonflies

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Interaction web showing the pathway by which fish
facilitate plant reproduction
Solid arrows direct interactions Dashed arrows
indirect interactions Sign expected direction
of the direct or the indirect effect
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How do Fish play a role?

• Larval stages of many freshwater organisms (i.e.
  dragonflies frogs) are vulnerable to a suit of
  aquatic predators (i.e. fish), whereas the adult
  stages are important consumers in terrestrial
  habitats
• Thus, the intensity of predation experienced by
  juvis in the aquatic habitat can be predicted to
  influence (indirectly) the intensity of predation
  imposed in turn by adults in terrestrial habitats

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The Site U of Florida

• 18 permanent ponds that differed in whether or
  not they have fish
• Chose 8 ponds (4 with fish, 4 without)
• There was no systematic differences between the
  ponds

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4 Aspects were tested to prove hypothesis

• Fish limit the size and abundance of larval
  odonates
• Correlation of fish presence with pollinator
  visitation
• Whether effects of fish indirectly influenced
  plant reproductive output
• Pollinator visitation would be lower near
  fish-free ponds for 2 reasons
• Adult dragonflies predate on pollinators
• Pollinators behaviourally avoid foraging near
  adult dragonflies

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How did they test it?

• Surveyed dragonfly abundances in and near
  fish-containing and fish-free ponds

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Results

• sorted dragonfly species into 3 size categories
  S, M, L
• Graph a Size distribution of dragonflies
• in ponds with fish, more M and L larval
  individuals and fewer S larval individuals
• Graph b Abundance of dragonflies
• abundance of adult dragonflies was lower near
  ponds with fish than without

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4 Aspects were tested to prove hypothesis

• Fish limit the size and abundance of larval
  odonates
• Correlation of fish presence with pollinator
  visitation
• Whether effects of fish indirectly influenced
  plant reproductive output
• Pollinator visitation would be lower near
  fish-free ponds for 2 reasons
• Adult dragonflies predate on pollinators
• Pollinators behaviourally avoid foraging near
  adult dragonflies

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How did they test it?

• Observed pollinator visitation on the most common
  shoreline flowering plant, Hypericum fasciculatum
  (aka St. Johns-Wort) in and near fish-free ponds
  and those containing fish

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Results

• Total number of pollinator visits to St.
  Johns-Wort was higher near ponds with fish
• Bars represent groups of pollinators
• black bars Diptera (flies)
• grey bars Lepidoptera
• white bars Hymenoptera (bees)
• St. Johns-Wort has evolved traits that attract
  bees, therefore
• bees are more effective at pollinating than
  flies
• Why does this matter?
• - effect is magnified

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4 Aspects were tested to prove hypothesis

• Fish limit the size and abundance of larval
  odonates
• Correlation of fish presence with pollinator
  visitation
• Whether effects of fish indirectly influenced
  plant reproductive output
• Pollinator visitation would be lower near
  fish-free ponds for 2 reasons
• Adult dragonflies predate on pollinators
• Pollinators behaviourally avoid foraging near
  adult dragonflies

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How did they test it?

• Performed pollen supplementation experiments to
  determine degree to which plant seed production
  was limited by pollen receipt at each pond
• How do pollinators drive plant population and
  community dynamics?
• If they dont visit too often, plants will
• fail to reproduce
• produce fewer seeds
• produce lower quality seeds

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Results

• Plants near fish-free ponds were more than 2X as
  pollen limited than plants near ponds with fish
• To make sure that the result they were getting
  was validthey tested another species of plant
  called Saggitaria latifolia
• also showed an increased number of pollinator
  visitations and therefore increased plant
  reproductive output at ponds with fish
• This indicates that the indirect effect of fish
  upon plant reproductive success is general

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4 Aspects were tested to prove hypothesis

• Fish limit the size and abundance of larval
  odonates
• Correlation of fish presence with pollinator
  visitation
• Whether effects of fish indirectly influenced
  plant reproductive output
• Pollinator visitation would be lower near
  fish-free ponds for 2 reasons
• Adult dragonflies predate on pollinators
• Pollinators behaviourally avoid foraging near
  adult dragonflies

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How did they test it?

• Over a 7-day period, they observed several
  predation events by 2 species of dragonflies
  (Anax junius, Erythemis simplicicollis) known to
  attack large insect species including pollinators

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Results
Found that 4 out of every 8 observed predation
events were on pollinators (bees, moths, and
flies)
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4 Aspects were tested to prove hypothesis

• Fish limit the size and abundance of larval
  odonates
• Correlation of fish presence with pollinator
  visitation
• Whether effects of fish indirectly influenced
  plant reproductive output
• Pollinator visitation would be lower near
  fish-free ponds for 2 reasons
• Adult dragonflies predate on pollinators
• Pollinators behaviourally avoid foraging near
  adult dragonflies

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How did they test it?

• Put cages around naturally occurring species of
  St. Johns-Wort near a pond with fish
• mesh size allowed for free visitation by most
  pollinators and precluded escape of 1 species of
  dragonflies (E. simplicicollis)

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Results

• Fewer visitors entered cages containing
  dragonflies than control cages (used a paired
  t-test to quantify t -4.2, p 0.02)
• Visitors that had entered cages with dragonflies
  forged on fewer flowers than visitors that
  entered cages not containing dragonflies (t
  -3.8, p 0.009)
• Resulted in H. fasciculatum flowers receiving
  fewer overall visits in the presence of a
  dragonfly

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Putting It ALL Together

• Strong linkages between consumers in aquatic
  terrestrial communities are not limited to this
  special case
• Many terrestrial predators, herbivores have
  larval aquatic stages
• Thus, aquatic predators might have a variety of
  consequences for interactions in neighboring
  terrestrial ecosystems

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Lets not forget

• Similarly, many organisms (ex. Salamanders) with
  terrestrial life-stages are important aquatic
  predators
• Thus, interactions in terrestrial ecosystems can
  cascade into aquatic ecosystems as well

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Article 2 Indirect effect of aquatic insect
emergence on terrestrial insect population
through by birds predation

• Purpose determine the effect of birds,
  subsidized by aquatic emergence, on the insect
  herbivores in a riparian deciduous forest

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Background

• Most systems have a heterogeneous pattern of
  resource distribution and this gives rise to a
  heterogeneous distribution of predators
• When distribution of 2 prey types differs, the
  distribution of predators is determined by the
  1st prey species and predation intensity on the
  2nd prey species can be indirectly affected by
  the distribution of the first
• This suggests a heterogeneous occurrence of
  indirect interaction between prey species sharing
  a common predator

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How does this relate?

• In a forest-stream ecotone
• Forest birds depend highly upon aquatic insects
  emerging from the stream early in spring
• Before spring leafing
• Terrestrial productivity 0
• Stream productivity is at its highest
• Why? More exposure to sunlight
• This asynchrony is responsible for a significant
  seasonal energy flow from stream to forest

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Top-down control of herbivorous insects by birds

• Ex. Marukami (1999)
• Showed that a population of leaf rolling
  Lipdoptera larvae on Japanese Lilac were
  controlled by birds
• Japanese lilac break bud earlier that other trees
• Thus, the foraging of insectivorous birds was
  concentrated on the Japanese lilac in early spring

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What did they predict? Hypothesis!

• An emerged aquatic subsidy supports a denser bird
  population along a stream compared with that of
  an upland forest
• Thus, there would be a decrease in herbivore
  population on riparian vegetation in early spring

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What did they use to test the hypothesis?

• Analyzed the distribution and abundance of birds
  on riparian and upland forest
• Assessed the degree by which forest birds are
  subsidized by emerged aquatic insects
• Addressed the manner in which the aquatic
  subsidies affect bird distribution within a
  forest and hence the herbivore population

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How did they test it?

• Bird Observations
• 4 dominant insectivorous bird species were
• Great tits, Marsh tits, Narcissus flycatchers,
  Willow Warblers
• Visiting frequencies to each plot and prey types
  were recorded every other day for a total of 10
  days
• Narcissus flycatchers did not utilize leaf
  rollers on lilac trees throughout the study
  period and were excluded from further
  investigation

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Results

• Bird visitation rates to riparian plots were
  greater than those to upland forest for great
  tits and crowned willow warblers
• No significant difference for marsh tits

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Results

• Riparian Plots
• all 3 bird species frequently utilized aquatic
  insects emerging from the stream (30-60 for each
  bird species)
• leaf rollers also utilized by all 3 bird species
  (rate of 15-50)
• Upland Plots
• birds rarely utilized insects emerging from
  stream
• leaf rollers were utilized 30-45 as well as
  other terrestrial insects
• Although rate of leaf roller utilization was low
  in riparian forest, amount of overall predation
  on leaf rollers was much higher in riparian
  forest because there was a greater bird
  population and therefore a greater visitation
  frequency

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What did they use to test the hypothesis?

• Analyzed the distribution and abundance of birds
  on riparian and upland forest
• Assessed the degree by which forest birds are
  subsidized by emerged aquatic insects
• Addressed the manner in which the aquatic
  subsidies affect bird distribution within a
  forest and hence the herbivore population

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How did they test it?

• Abundance of flying insects was surveyed by a
  malaise trap
• Trap was set during the middle of the study
  period
• Collected arthropods were preserved in 70
  ethanol and sorted into terrestrial and aquatic
  insects, component species being identified to
  order
• Biomass of each order and family was measured as
  wet mass and the dry mass was estimated
  subsequently
• Insect masses were then compared between riparian
  and upland forests separately for terrestrial and
  aquatic insects

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Results

• Biomass of aquatic and terrestrial insects in
  riparian and upland forests caught by malaise
  trap (vertical bars indicate std. error)
• no significant difference occurred in
  terrestrial prey biomass between riparian and
  upland forests (P0.786)
• aquatic prey biomass was much higher in riparian
  forest (P0.013)

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What did they use to test the hypothesis?

• Analyzed the distribution and abundance of birds
  on riparian and upland forest
• Assessed the degree by which forest birds are
  subsidized by emerged aquatic insects
• Addressed the manner in which the aquatic
  subsidies affect bird distribution within a
  forest and hence the herbivore population

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How did they test it?

• Bird exclusion experiment
• 5 randomly selected trees in 3 riparian and 3
  upland plots were enclosed by cages of 15mm nylon
  mesh net that allowed most insects but no birds
  to pass through
• additional 30 non-enclosed tress (15 from
  riparian and 15 from upland) were selected to
  controls
• of 3 dominant leaf roller species per shoot was
  calculated at the end of the experiment by
  counting the numbers of leaf rolls and shoots on
  each individual tree
• effects of bird removal on the of leaf rollers,
  treatment and site (riparian or upland) being the
  factors were detected by 2-way ANOVA

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Results

• Impacts of birds differed among the leaf roller
  species
• H. foederatana s decreased because of
  predation by birds, particularly in riparian
  forest plots as shown by the significant effects
  of both treatment and site with the interaction
  also being significant
• no significant bird effects found on A. viola or
  Z. corpulentana leaf roller s
• Indicates that the latter 2 species are not
  utilized by birds

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Final thoughts

• Although the birds in the riparian forest derived
  much of their energy from aquatic insects, about
  2/3 of the diet consisted of terrestrial prey, in
  particular the leaf rollers
• The greater bird population and therefore greater
  visitation frequency resulted in greater
  predation pressure on leaf rollers in the
  riparian forest
• Accordingly, the birds thus subsidized can
  depress the population of H. foederatana to
  greater effect in the riparian forest than in the
  upland forest indirect effect of an aquatic
  prey input on a terrestrial herbivore through
  bird predation
• This study also shows thats aquatic insect
  emergence negatively affects leaf rolling
  Lepidoptera larvae through forest birds

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Future Research

• Further examination of the complex food web
  network and the importance of allochthonous prey
  input on the dynamics and structure of
  communities in heterogeneous landscapes

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References

• Knight, T. M., McCoy, M. W., Chase, J. M., McCoy,
  K. A., Holt, R. D. (2005). Trophic cascades
  across ecosystems. Nature 473, 880-883.
• Murakami, M., Nakano, S. (2002) Indirect effect
  of aquatic insect emergence on a terrestrial
  insect population through predation by birds.
  Ecology Letters 5, 333-337

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The END!!!

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