Transcript Lotic EcologyPT2

Shredders and Gougers
• Consume CPOM (> 1 mm mesh) - leaves, etc., and thus depend heavily on
seasonal inputs of leaves to the stream
• Mouthparts usually “chewing” (e.g., many Trichoptera)
• Leaves entering the stream are first “conditioned” by bacteria and fungi,
reducing their toughness and creating more digestible proteins and
carbohydrates for the invertebrates
• Most shredders can’t digest cellulose, but Tipula harbors endosymbiotic
bacteria capable of cellulose digestion
• Gougers consume wood, and are often found inside submersed snags
(e.g., the chironomid Brillia); these are unusually slow growing taxa
• Their feces form an important constituent of FPOM
Fam. Taeniopterygidae; O. Plecoptera
Fam. Tipulidae; O. Diptera
Filter Feeders
• Consume suspended particles (FPOM), including
phytoplankton, bacteria and seston (temporarily suspended
particles)
• Frequently found below lakes and reservoirs
• Includes many Trichoptera, e.g., Hydropsychidae
• Blackfly (Simuliidae) larvae have cephalic fans which are held
at the edge of the boundary layer and trap particles, which
are removed by labral bristles and transferred to the mouth
• Flocculation of DOM by bacteria converts it to a form
consumable by filter feeders
Filterers
Fam. Hydropsychidae; O.
Trichoptera
Fam. Philopotamidae; O.
Trichoptera
Fam. Unionidae
Fam. Simuliidae; O. Diptera
Deposit Feeders
• Also feed on FPOM, but by gathering it from the
sediments; the FPOM includes bacteria, algae,
detrital particles, of widely varying food quality
• Typically brushlike mouthparts
• Includes many mayflies, midges, crustaceans
Fam. Chironomidae; O. Diptera
(many are deposit feeders)
Scrapers/Grazers
• Specialists on periphyton on solid surfaces
• Mouthparts designed to shear attached algae
from the substratum (e.g., scythe-like
mandibles of the caddisfly Glossosoma; the
radula of snails)
Fam. Heptageniidae; O. Ephemeroptera
Fam. Psephenidae; O. Coleoptera
Scavengers
Many macrocrustacea (amphipods, isopods,
crayfish) opportunistically consume animal,
algal and plant material
O. Amphipoda
O. Isopoda
Invertebrate Predators
• This group is highly diverse, both in
microhabitat and food specialization
– many surface-feeding Hemiptera
– sit-and-wait benthic predators (e.g., dragonflies)
– fluid specialists (e.g., leeches), etc. etc.
• Some taxa are predaceous for only part of the
life cycle (e.g., later instar Tanypodine
chironomids, larval hydrophilid beetles)
Predators
fam. Tabanidae; O. Diptera
fam. Gerridae; O. Hemiptera
Fam. Hydrophilidae; O.
Coleoptera
fam. Nepidae; O. Hemiptera
Fam Perlidae; O. Plecoptera)
Predator Behavior
• Hunting Behavior
– 1. stalking/active pursuit (e.g., perlid stoneflies)
– 2. ambush (e.g., hemipteran family Nepidae)
• Prey detection Mechanisms
– 1. tactile (e.g., the stream damselfly Calopteryx)
– 2. Visual (e.g., most other damselflies)
– 3. Chemical (perlid stoneflies search in an upstream,
following prey chemical trails)
Calopteryx
visual damselfly
Prey Defenses
• Primary (operate regardless of predator’s proximity)
– a. refuges (e.g., many Trichoptera, chironomids)
– b. crypsis
• Secondary (behavioral responses)
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–
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a. Thanatosis (feigning death) (e.g., some Coenagrionid damselflies)
b. Secondary Compounds (e.g., many Coleoptera and Hemiptera)
c. Group Defense (e.g., Gyrinids may confuse predators)
d. Active (e.g., strigulating in the beetle Tropisternus; use of the
scorpion posture in ephemerellid mayflies)
Ephemerellid mayflies produce
“scorpion posture” when
threatened by stonefly
predators
Macrophyte Consumers
• Leaf and stem feeders
• Many Lepidoptera, some chironomids, some
beetles, some Trichoptera
Fam. Chrysomelidae; O. Coleoptera
Fam. Pyralidae; O. Lepidoptera
Fish predation
• Evolutionary effects on invertebrate behavior/morphology
– (e.g., Trichopteran cases provide protection against fishpredators)
• Effects of fish on stream inverts much harder to detect than in
lakes, owing to the effects of drift
•
The Trophic Cascade
– The basic idea is that the food web can be simplified to a food chain in some streams. An
increase in size in a top trophic level may then reduce the size of the level below, increase
the size of the level below that, etc.
Piscivores
Invertivores
Inv.
Grazers
Periphyton
Invertiv.
Inv. Grazers
Periphyton
The River Continuum Concept
As stream order increases:
– a. the influence of the riparian
canopy diminishes as a light
interceptor
– b. production by periphyton and
macrophytes increases
– c. inputs of leaf litter decline
– d. shredders are largely replaced
by FPOM feeders
– e. P/R increases, but then may
decrease once more in very large
rivers
– f. plankton communities become
sustainable in river systems
Vannote et al. (1980)
Aquatic Insect Respiration
• Tracheal system
– Usually consists of a spiracle leading to a trachea, then branching
tracheoles
• Atmospheric oxygen obtained by
– visiting the surface
– Transporting a bubble underwater (“physical gill”).
– e.g., most Hemiptera and Coleoptera
• Dissolved oxygen extracted from water
– e.g., into gills or across the integument
– e.g., mayflies, stoneflies, odonates, dipterans
– Oxygen ultimately reaches “closed tracheal system” (no spiracles)
The Physical Gill
– The bubble is brought
down from the surface
– As oxygen is drawn from
the bubble through the
spiracles into the insect,
oxygen from the water
diffuses into the bubble
(greatly prolongs its use)
Coleopteran
Hemipteran
Oxygen from Plant Stems
The beetle Donacia and its
relatives tap into the roots of
water lilies and other submersed
plants
Hemoglobin as an adaptation to lowoxygen environments
• Enhanced ability to
take up oxygen from
oxygen-poor
environments
Midge (Chironomus) larva
Aquatic Insects
• Typically the immatures are found in water; the adults may either aquatic
or terrestrial. The change from water to land during the life cycle may
require considerable ontogenetic modification of body form. Two general
and distinct types of life histories:
• Hemimetabolous: (Odonata, Ephemeroptera, Plecoptera, Hemiptera)
egg  larva or nymph  adult
• Holometabolous: (Megaloptera, Neuroptera, Trichoptera, Coleoptera,
Diptera, Lepidoptera)
egg  larva  pupa  adult
– The pupal stage may either be motile or non-motile, and is the principal
means for reorganizing the body structure
Life History
Stages
A. Holometabolous
(e.g., Trichoptera)
B. Hemimetabolous
(e.g., Plecoptera)
Mayflies are hemimetabolous
• Hexagenia mayflies typically
spend a year as larvae,
emerge as a pre-reproductive
adult (“dun”), then molt
again to reproduce
(“spinner”). There is no
pupal stage.
Holometabolous Life Cycle
Pupa
• Whirligig beetles (fam.
Gyrinidae) have
morphologically very
distinct larval, pupal and
adult stages.
Order
More primitive
insect orders have
more larval instars
Typical No.
larval Instars
Ephemeroptera
15-25
Odonata
10-12
Plecoptera
12-22
Hemiptera
5
Megaloptera
10-11
Coleoptera
3
Trichoptera
5
Diptera
4-7
Time to complete the
life cycle
• univoltine
– Species which require one year to
complete the life cycle
• bivoltine
– two generations per year
• Multivoltine
– > 2 generations/yr
• Larger, or higher latitude, taxa may
require more than one year to
complete the life cycle, and two or
more distinct size classes may thus
co-occur in the same location.
Larval hellgrammites (O. Megaloptera)
may require 5-7 years before emerging
to become adults
Adult Megalopteran
Hemimetabolous or holometabolous?
Overview of the Orders of Aquatic Insects covered in
lab
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Ephemeroptera: Mayflies
Plecoptera: Stoneflies
Odonata: Dragonflies and Damselflies
Trichoptera: Caddisflies
Hemiptera: True Bugs
Coleoptera: Beetles
Megaloptera: Alderflies and Dobsonflies
Diptera: True Flies
A few examples are shown in the slides that follow; the complete list of
taxa, with slides, is provided in the “Macroinvertebrates for Practicum”
file posted on Blackboard