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Outline. Quiz Assignment: Peer review due after Spring Break Lecture: Invasive species and communities Break Second half of WI Fishes (ID’s). Invasive species and communities. A prelim exam question….

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Assignment: Peer review due after Spring Break

Lecture: Invasive species and communities


Second half of WI Fishes (ID’s)

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Invasive species and communities

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A prelim exam question…

“Are invasive species more likely to have large impacts on native communities via predation or via competition?”

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First, communities…

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Competition is important...just not as important as predation

5 Basic types of species interactions

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What is competition?

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space or habitat


Competition ...common use of a limited resource

What can be limiting....?

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Between and within species

Intraspecific competition

Interspecific competition

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Population Abundance


How do we see it or measure it?

  • Individual Responses

  • Behavior – feeding rate

  • Physiology – growth rate

  • Morphological – body size

  • Population responses

  • Abundance

  • Distribution

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3 types of competition

Interference competition

Exploitation competition

Apparent competition

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Interference competition - occurs directly between individuals via aggression etc. when the individuals interfere with foraging, survival, reproduction of others, or by directly preventing their physical establishment in a portion of the habitat.





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Exploitation competition - occurs indirectly through a common, limiting resource, which acts as an intermediate. Ex. depletes the amount of food or fill up all the available space.










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Apparent competition - occurs indirectly between two species which are both preyed upon by the same predator.













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Resource partitioning

Population Abundance

Resource Gradient

Competition's role in ecology and evolution

"species packing"

Population Abundance

Resource Gradient

Evolution to minimize competition

Difficult (or impossible) to prove

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Species evolve within communities to utilize resources along a gradient

  • Food particle size

  • Temperature

  • Habitat

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Warmer Temps Cooler Temps

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Lake Tanganyika

Lake Malawi

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Community Assembly and Invasive Species

  • Sequence of invasions is important

  • As species #’s increase, so does partitioning of resources

  • Eventually, resources cannot be partitioned any further, and species will be excluded

  • Logical extension: Species-rich environments will be resistant to invasions

    • This has not held true due to disturbance, importance of abiotic factors, extirpations, unsaturated communities

    • However, diverse communities may be less impacted

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M.J. Vander Zanden. 2005. The Success of Animal Invaders, PNAS 102: 7055-7056

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Invasive Species

  • Why should we care?

    -Leading cause of global biodiversity loss

    -Particularly severe in freshwater ecosystems

    - Contributing factor in 68% of fish extinctions in US and Mexico

    - Cost $137 billion/year in US alone

    - Numbers are increasing

  • BUT…most do not establish or have negative effects…

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Why are species introduced?

  • Food

  • Familiar or “superior” species

  • Enhancement (or creation) of fisheries

  • Manipulation of systems (biological control)

  • Accidental

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Accidental Introductions

  • Canal building

  • Ballast water

  • Bait bucket introductions

  • Hitchhiking on boats

  • Angler introduction

  • Aquarium escape

  • Aquaculture escape

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Invasive species that affect the ecology of native Wisconsin Fishes

Pelagic planktivores - Alewife, Rainbow smelt, white perch, bythotrephes

Benthic omnivores - round goby, rusty crayfish, common carp

Pelagic piscivores – Pacific salmon, brown trout, rainbow trout

Pelagic/benthic parasite – Sea lamprey

Stream insectivores – brown trout, rainbow trout

Pelagic filter-feeders – silver carp, bighead carp

Benthic filter-feeders – zebra mussel, quagga mussel

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Steps to Invasiveness


Establishment and Integration

Adapted From Vander Zanden et al. 2004


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  • Niche: the ecological role of a species in relation to other species and the non-biological environment

  •  The niche represents the range of conditions within which a species can survive and reproduce

  • The niche of a species in the absence of competition is called the fundamental niche.

  • The niche of a species in equilibrium with competitors is called the realized niche

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Fundamental vs. Realized Niche

Realized niche

Prey Consumed


Fundamental niche


Prey Size

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Impacts: Misunderstanding of Niche

  • Niche changes throughout life history

  • Forage fish can compete with/prey upon juvenile game fish (Example: smelt, alewives)

  • Introductions to fill “vacant” niches

  • Assumption: An organism will occupy the same habitats and roles in a new system as it does in native range

    • Not always true – organism may be bound geographically or ecologically in native range

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  • Classic example of changes in realized niche: Opossum shrimp (Mysisrelicta)

  • Introduced to enhance fish populations

  • Detritus/phytoplankton feeder in native ecosystem (realized niche)

  • Niche expansion upon introduction lead to zooplankton depletion – eliminated food resources for populations it was supposed to enhance

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Impacts: Mechanisms

Species level

  • Competition (interference: brown/brook trout exploitation: alewives/ coregonids)

  • Predator-Prey (Nile perch/ cichlids)

  • Parsite-Host(Crayfish)

    Community level

  • Trophic Cascade

  • Ecosystem Engineer (alters abiotic factors)

  • Hybidization

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Management of Invasive Species


  • Chemical control

  • Biological control

  • Mechanical control

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Management of Invasive Species


  • Risk analysis approaches that incorporate ecological, economic, and social welfare show that prevention is cost-effective

  • Predictions of invaders with the biggest impact, or predictions of which ecosystems are most vulnerable to a specific invader, are emerging as standard methods for directing management.

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Predictions of Invasive Species

Mercado-Silva, N., J.D. Olden, J.T. Maxted, T.R. Hrabik, M.J. Vander Zanden. 2006. Forecasting the spread of invasive rainbow smelt in the Laurentian Great Lakes region of North America. Conservation Biology 20: 1740-1749.

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More predictions…

42% (1,369 km) identified as suitable

(7% of state)

44% (8,878 km) identified as suitable

Kornis, M.S., and Vander Zanden, M.J. 2010. Forecasting the distribution of the invasive round goby (Neogobisu melanostomus) in Wisconsin tributaries to Lake Michigan. Can. J. Fish. Aquat. Sci. 67: 553-562.

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  • Invasive species are an increasingly important threat to native species and biodiversity

  • Invasive species affect native ecosystems through numerous pathways that are not mutually exclusive

  • Invasive species management is sometimes possible once the invader has established

  • Prevention of invasions is key for future management

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