Ecology Exam 2 Flashcards
(37 cards)
Macroparasites:
Large species such as arthropods, ticks, and worms.
Microparasites:
Microscopic, such as viruses, bacteria, fungi and protists.
Parasitoids:
Insects whose larvae feed on a single host and almost always kill it.
How many parasites can attack a species?
Do parasites adapt to their host?
Specialization helps explain what?
Most species are attacked by more than one kind of parasite; even parasites have parasites.
Many parasites are closely adapted to particular host species.
Specialization helps explain why there are so many species of parasites.
Ectoparasites:
Where do they live?
Plant example
Fungal example
Animal example
Advantages
Disadvantages
Ectoparasites live on the outer body surface of the host.
Plant ectoparasites include dodder and mistletoe.
Fungal parasites include mildews, rusts, and smuts.
Animal ectoparasites that eat plants and live on their outer surfaces can be thought of both as herbivores and parasites.
Aphids, whiteflies, scale insects, beetles, nematodes, athlete’s foot fungus, fleas, mites, lice, ticks. Many also transmit pathogens.
Advantages: disperse easy, safe from host immune system
Disadvantages: exposed to enimies, external enviorment, feeding is hard
Endoparasites:
Where do they live?
Example
Advantages
Disadvantages
Endoparasites live inside their hosts.
Most don’t eat host tissue, but rob the host of nutrients.
Tapeworms inside stomach
Some live in host’s tissues or cells:
Yersinia pestis, bacterium that causes the plague
Mycobacterium tuberculosis, bacterium that causes tuberculosis
Coronavirus SARS-CoV2, which causes COVID-19
Advantages: easy feeding, protected from external enviorment, safe from enimes
Disadvantages: vunarbale to host immune system and dispersal is hard so must rely on complex life cycle and ensalve host
Animal hosts have many kinds of defense mechanisms:
Protective outer coverings include skin and exoskeletons.
Immune systems, biochemical defenses, defensive symbionts.
Vertebrate immune systems
“Memory cells” recognize microparasites from previous exposures.
Other cells engulf and destroy parasites or mark them with chemicals that target them for later destruction.
Some animals eat specific plants to treat or prevent parasite infections.
Woolly bear caterpillars switch from their usual food plants to poison hemlock when parasitic flies lay eggs on their bodies.
Chimpanzees infected with nematodes eat a plant that contains chemicals that kill or paralyze the nematodes (Huffman 1997).
Plants defense systems:
Resistance genes
Nonspecific immune responses such as antimicrobial and antifungal compounds
Chemical signals that “warn” nearby cells of imminent attack
Chemicals that stimulate deposition of lignin, making a barrier to an invader’s spread
Plants have many chemical weapons called secondary compounds.
Counter Defenses: Parasites
lamellocytes
Two challenges in the human host:
Parasites are under strong selection pressure to develop counter defenses
Ectoparasites must have mechanisms to penetrate external defenses or toxic compounds produced by plants, challenges similar to those faced by herbivores and predators.
Endoparasites must cope with defenses found inside the host.
Some hosts can encapsulate endoparasites or their eggs to make them harmless.
Some insects have lamellocytes—blood cells that can form multicellular capsules around large objects such as nematodes
Two challenges in the human host:
Merozoites multiply in red blood cells, but these cells don’t divide or grow, and don’t import nutrients
Infection by Plasmodium causes red blood cells to have an abnormal shape, which are destroyed in the spleen
Host-parasite coevolution:
arms race
When parasites and hosts each possess specific adaptations, it suggests that the species have undergone coevolution.
Coevolution occurs when populations of two interacting species evolve together, each in response to selection pressure imposed by the other.
Transmission is a crucial step in all pathogen/parasite life cycles. Certain species have evolved complex traits that increase their chances to find and invade new hosts.
Some of the best examples of coevolution come from the “arms race” of host parasite evolution. An arms race may stop because of trade-offs:
A trait that improves host defenses or parasite counter defenses may reduce some other aspect of growth, survival, or reproduction.
Parasites Can Change Ecological Communities:
Parasites can change the outcome of species interactions, community composition, and even the physical environment.
Predator–prey interactions
Parasites can affect the physical condition of infected individuals.
Predators may be less able to catch their prey, or prey less able to escape predation.
Parasites can also change the behavior of their host
Changes in community structure: A parasite that attacks a dominant competitor can suppress that species, causing other species to increase.
Climate change is affecting distribution of diseases
The niche:
Fundamental niche:
Realized niche:
Fundamental niche: The full set of resources, plus other abiotic requirements of a species - the potential use of resources - all the environments can exist in - entire pizza
Realized niche: The restricted set of resources that a species is limited to, due to species interactions - organism interacting with each other - but shares pizza
The realized niche is therefore usually smaller than the fundamental niche.
Competition:
1. Interspecific competition:
2. Intraspecific competition:
Competition: Non-trophic interaction(organisms that share trophic level not interacting) between individuals of two or more species in which all species are negatively affected by their shared use of a resource.
- Interspecific competition: Between members of different species
- Intraspecific competition: Between individuals of a single species
Competition mechanisms
A commonly used binary classification of mechanisms:
- Exploitative
- Interference
Allelopathy:
- Exploitative (mutual depletion of shared resources) - two plants in same soil is depleting a shared resource
- Interference (direct interactions between competitors)
Individuals of one species grow on or shade other species, reducing their access to light
Allelopathy: Plants of one species release toxins that harm other species
Carnivores fighting over animal prey
Allelopathy:
Secrete ‘juglone’ : inhibits the growth of other plants
Black walnut trees are so infamous the term “walnut wilt” has been coined
Tree-of-heaven (Ailanthus altissima), sugar maple (Acer saccharum), hackberry (Celtis spp.), and American elm (Ulmus americana) also produce allelochemicals
Allelopathy: Plants of one species release toxins that harm other species
Competition intensity
Competition intensity depends on
- Resource type
- Resource availability
- Density of competing individuals
Belowground competition was most intense in nitrogenlimited plots
Aboveground competition for light increased when light levels were low
Density dependence
Increased neighborhood density results in stronger competition
Negative density dependence important force shaping forest diversity
Competition is often asymmetrical
Experiment silica
Competition reduces available resources for both individuals/species and abundance of both is reduced to some extent
But effects of competition are often unequal, or asymmetrical; one species is harmed more than the other
Example: When one species drives another to extinction
Experiment: growing them alone and in competition with each other
When each species was grown alone, a stable population size was reached and put down the silica
When grown together, they competed for silica, and one species drove the other to extinction
Competitive outcomes
1. Competitive exclusion:
- Coexistence:
- Competitive exclusion: dominant species prevents another species from using essential resources; the inferior species may become locally extinct
- Coexistence: living together at the same time or in the same place despite competing for limiting resources (most common)
Competitive exclusion
competitive exclusion principle:
Resource partitioning:
Experiments on these and many other species led to the competitive exclusion principle:
Two species that use a limiting resource in the same way (AKA sharing the same niche) cannot coexist indefinitely
Resource partitioning: Species using a limited resource in different ways are able to coexist (lead to competitive coexistence).
One species absorbs green wavelengths most efficiently, the other absorbs red most efficiently
Each species could survive when grown alone in either wavelength
When grown together, one drove the other to extinction, depending on light wavelength
Coexistence
Coexistence can occur because of resource partitioning:
Interspecific competition can cause
Character displacement
Coexistence can occur because of resource partitioning:
a population evolves to make use of a different resource
a different area of the habitat
or feeds during a different time of day
Interspecific competition can cause niche differentiation – competing species use the environment differently in a way that leads to coexistence
Two species with essentially the same niche cannot coexist because one will always out-compete and displace the other
Character displacement
When two species compete for resources, natural selection may favor phenotypes that allow them to partition their limiting resources.
Finches inhabiting the Galápagos archipelago are an iconic model for studies of character displacement
Closely-related species differ in beak size
Each species eats a different type of seed:
On islands with only one of the species, beak sizes are similar.
On islands that have both species beak sizes are small and large
Factors affecting competition
The outcome competition between species can be changed by features of the:
The outcome competition between species can be changed by features of the:
1. physical environment
2. disturbance
3. interactions with other species
- Physical environment
Chthamalus is found in upper intertidal zone
Balanus is found in lower intertidal zone (will desiccate higher intertidal zones)
Compare growth rates, survival, and/or reproduction of both species, alone and together
Chthamalus is perfectly capable of surviving in the mid-intertidal zone in the absence of Balanus
Experiment: remove Balanus, compare to control
The realized niche of Chthamalus is a fraction of its fundamental niche due to competition with Balanus
- Disturbance
Disturbances such as fires or storms can kill or damage some individuals, while creating opportunities for others
Some species can persist in an area only if disturbances occur regularly
Example: forest plants that need sunlight are found only where disturbance has opened the tree canopy
