Comparative Ecology: Parasitism, Competition, and Succession

Parasitism

when one organism feeds on another, but does not normally kill it outright

Predation

involves a predator killing and consuming its prey

Kleptoparasitism

When one species steals resources from another

Microparasites

parasites too small to be seen with the naked eye

Macroparasites

parasites large enough to be seen with the naked eye

Parasitoids

similar to microparasites but they ultimately sterilize, kill, and (sometimes) consume the host

Ectoparasites

live on the outside of the host; tend to be polyphagous, having many host species (like leeches)

Endoparasites

live on the inside of the host; seems to require greater specialization; need to prevent the host's defenses to stay alive; more often monophagous

Holoparasites

lack chlorophyll and are totally dependent on the host plant for water and nutrients

Hemiparasites

photosynthesize but they lack a root system to draw up water & depend on their host for that function

Definitive hosts

the host in which parasites exhibit sexual reproduction

Intermediate hosts

species containing non-reproducing forms of the parasite

Parasites modifying host behavior

Starlings contain adult parasitic worm; the eggs are passed in the bird's feces; pillbugs eat the feces and ingest the parasitic eggs; juvenile parasites change the pillbug's behavior, causing it to wander out into the open; songbirds prey on pillbugs, completing the life cycle

Schistosomiasis

It poses a major global health issue with over 200 million people infected, especially in developing countries

Life cycle of Plasmodium

The malaria parasite, a single-celled species in the genus Plasmodium has a complex life cycle involving two hosts: mosquitoes and vertebrates.

Plasmodium's effect on mosquitoes

Plasmodium interferes with the ability of the mosquito to draw up blood from its hosts.

Increased attack rates of mosquitoes

This increases the number of attacks the infected mosquitoes make in order to try and obtain enough blood.

Brood parasitism

A specific kind of kleptoparasitism in which individuals manipulate others to feed and look after their young

Mafia hypothesis

Proposes that cuckoos or cowbirds repeatedly check their host's nests and destroy all of their eggs if their owner is not present

Innate immunity

Constituted by the body's defenses present at birth. Example: the skin and mucous membranes protect the body from invasion by microparasites.

Acquired immunity

Develops after the body is exposed to a parasite. Example: viruses, bacteria, toxins, cancers, and even pollen may trigger defenses that target specific substances.

Parasite-removal studies

Investigators remove the parasites and re-examine the densities of their host populations.

Parasites

Small sizes and the unusual life history of many parasites makes them difficult to remove from hosts.

Effects of Parasites

Many parasites impair the health of their hosts rather than kill them directly, making the effects of parasites on host populations even more difficult to gauge.

Weakened Hosts

Weakened or unhealthy hosts may fall prey to predators more often than healthy, unparasitized hosts.

Malaria Inoculation

Some bird populations have been innoculated against malaria by capturing nesting adults and administering primaquine in solution.

Sudden Oak Death Syndrome

A recent and severe disease of many plant species in California, which causes leaf spots, oozing of dark sap, and twig dieback.

Biological Control

The use of natural enemies, including parasitoids and predators.

Factors Influencing Biological Control Success

5 necessary attributes: general adaptability to the environment, high searching capacity for hosts, high rate of increase relative to the hosts, good dispersal ability, minimal time lag effects in responding to changes to hosts numbers.

Critical Threshold Density Formula

Nt=1/BL

Transmission Rate (B)

B - transmission rate of the disease.

Infectious Period (L)

L - the average period of time over which the infected host remains infectious.

Climate Change and Parasites

Global warming will hasten disease development and transmission of diseases.

Predicted Diseases from Climate Change

Wildlife Conservation (2008) predicted that a 'deadly dozen' diseases from avian flu to yellow fever were likely to spread because of climate change.

Plant Pathogens and Temperature

Many plant pathogens cause greater damage at higher temperatures than lower ones.

Vector-borne Diseases

Vector-borne diseases such as African typanonomsomiasis, malaria, Lyme disease, yellow fever, and dengue fever have increased in incidence or range in recent years, particularly at higher altitudes.

Intraspecific Competition

Competition between the same species.

Interspecific Competition

Competition between different species.

Exploitation Competition

Organisms compete through the consumption of a limited resource.

Interference Competition

Individuals interact directly with one another.

Amensalism

A biological interaction where one organism harms another without any benefit to itself.

Example of Amensalism

Where one species produces and secretes chemicals from its roots that inhibit the growth of another species.

Apparent Competition

Two species do not compete for the same resource but they do share at least one natural enemy.

Associational Susceptibility

Occurs in plants where herbivores spill over from one species to another.

Example of Associational Susceptibility

In northern Utah, the caterpillars of the moth, Alsophila pometaria, known as fall cankerworms, prefer to feed on box elder trees and are rarely found on isolated cottonwood trees.

Factors Affecting Competition

Parasites, temperature, moisture.

Guild

Connotes a group of species that feed on the same resource and in the same way.

Enemy Release Hypothesis

Suggests invasives are released from their natural enemies and can devote more resources to growth, and thus competition. This leads to the evolution of increased competitive ability.

Superior Competitor Hypothesis

Suggests invasives are more efficient users of natural resources than natives or non-invasives.

Propagule Pressure Hypothesis

Suggests invasives produce more progeny than some native species, and by sheer weight of numbers this permits them entry into natural communities.

Lack of environmental constraints hypothesis

Suggests pre-adaptation of some invaders to existing environmental conditions.

Biological control

Natural enemies such as predators and parasites are released against pests. Often these natural enemies are the ones that control the pest in its native country.

Lotka-Volterra model for Species 1

(dN1/dt)=r1N1 X ((K1-N1)/K1)

Lotka-Volterra model for Species 2

(dN2/dt)=r2N2 X ((K2-N2)/K2)

R*

The resource level at which organismal gains by growth equal losses to predators or disease.

Competitive exclusion principle

Complete competitors cannot coexist; Gause concluded that species with exactly the same requirements cannot live together in the same place and use the same resources, that is, occupy the same niche.

Resource partitioning

The differentiation of niches, both in space and time, that enables similar species to coexist in a community.

Example of resource partitioning

MacArthur found that four of the species occupied different heights and portions in the tree and each probably fed on a different range of insects.

Proportional similarity

PS=Σpi

Predator-mediated coexistence

Dominant competitors will never be able to eliminate poor competitors.

Character displacement

Tendency for two species to diverge in morphology, and thus resource use because of competition.

Example of character displacement

When three species of finch, Geospiza fuliginosa, G. fortis, and G. magnirostis, were found together on the islands of Pinta and Marchena their bill depths were different.

Facilitation

The enhancement of a population of one species by another.

Mutualism

An interaction between two species in which both benefit.

Commensalism

An association between two organisms in which one benefits and the other is not harmed.

Obligate mutualism

Where neither species can live without the other; lichens are an inseparable mix of fungi and algae.

Facultative mutualism

The interaction is beneficial but not essential to the survival and reproduction of either species; many ant species exist in mutualistic relationships with aphids.

Dispersive mutualism

Includes plants and the pollinators that disperse their pollen, and plants and the fruit eaters that disperse the plant's seeds.

Defensive mutualism

Involves an animal defending a plant or an herbivore.

Resource-based mutualism

Involves the increased acquisition of resources for both species.

Pollination syndromes

Some pollinators visit only flowers of one particular plant species.

Mutualistic cheating

In Maine, the grass pink orchid produces no nectar but receives pollinators because it mimics the rose pogonia.

Competition avoidance hypothesis

Competition with the parent plant is avoided, but there is no guarantee that the seed will fall into an optimal habitat.

Predator escape hypothesis

Seed predators congregate under parent trees to feed on the fallen seeds, so well-dispersed seeds suffer less predation.

Colonization hypothesis

Constantly shifting environmental conditions for seed germination means that parental location is not always a good predictor of seedling success.

Directed dispersal hypothesis

Some dispersers distribute seeds into optimal sites.

Myrmecochory

The seed-dispersal by ants.

Elaiosomes

Tropical and temperate plants that produce seeds with lipid-rich attachments called elaiosomes or arils.

Beltian bodies

Protein-rich granules.

Nectaries

Nectar-producing glands that are physically apart from the flower.

Mycorrhizae

Require soluble carbohydrates from their host and they supply mineral resources and water.

Endosymbiosis theory

A relationship whereby two species live in close association with one another.

Gene megacenters of cultivated plants

Middle east - wheat; China - rice; South east asia - bananas; Africa - yams; Central america - potatoes; Mediterranean - grapes.

Inquilinism

Occurs when one species uses a second species for housing (orchids grow in forks of tropical trees).

Phoresy

When one organism uses a second organism for transportation (flower-inhabiting mites travel between flowers in the nostrils of humming birds).

Metabiosis

An organism uses something produced by the first, usually after its death (hermit crabs use snail shells for protection).

Associational resistance

Palatable plants can gain protection against herbivores through an association with unpalatable neighbors.

Bottom-up model

Proposes that the host plant quantity or quality limits the density of herbivores, which in turn sets limits on the abundance of predators.

Top-down model

Proposes that plant densities are limited by herbivores and that herbivores are limited by predators.

Nitrogen-limitation hypothesis

Suggests that organisms select their food in terms of the nitrogen content of the tissues.

Trophic cascade

Also referred to as top-down control; effects of top-down control may percolate down from predators through herbivores to plants.

Green earth hypothesis

Since the Earth appears 'green', and plants are common, herbivores must have little impact on plant abundance.

Ecosystem exploitation hypothesis

Strength of mortality factors varies with plant productivity, the rate of production of plant biomass.

Environmental stress hypothesis

In stressful habitats higher trophic levels have little effect because they are rare or absent, and plants are affected mainly by environmental stress.

Key factor analysis

k=logNt - logN(t+1).

Indispensable mortality

Number of adults merged X MSR of a particular stage.

Compensatory mortality

When new mortality sources reduce other natural mortality sources, resulting in no overall increase in the total mortality rate.

Additive mortality

When new mortality sources increase the total mortality rate without any offsetting reduction in other natural causes of death.

Genetic diversity

Genetic variation within a species.

Community diversity

Variation among communities.