Recap Competition model and outcomes Asymmetric competition Habitat

Recap Competition model and outcomes Asymmetric competition Habitat productivity

13. 4 Habitat productivity can influence competition between plant species Two hypotheses: 1. Plants compete more intensively when mineral nutrients are less abundant in the soil (By Grubb and Tilman) Plants compete more intensively when nutrients are less. High nutrients are less likely to limit plant population; thus the intraspecific competition is weak. 2. Competition is less intense when water and nutrients are less abundant (Grime and Keddy) Competition for light is more important than competition for nutrients; limit in water and nutrients would limit the population growth to a certain point that individual plants are widely spread and do not compete for light. Difference between these hypotheses lies in the relative importance placed on belowground aboveground competition for resources --Light or nutrient. (Debate)

Habitat productivity can influence competition between plant species Smooth cordgrass saltmeadow cordgrass, black grass, alder

Habitat productivity can influence competition between plant species Saltmeadow vs Smooth Blackgrass vs saltmeadow Fertilization alters the outcome of competition by removing nutrient limitation on stress-tolerant plants, expand, away from water.

13. 5 Competition may occur through direct interference n n Exploitation: indirectly influencing each other by consuming the same resources (eat same grass by zebras , compete for water uptake by trees, indirectly) Interference: direct influencing each other by preventing others to occupy a habit or access resources (birds, bees chase birds and bees, animals release toxic chemicals). n Meadow vole (wet) and mountain vole (dry). (Asymmetric competition also)

Allelopathy (chemical competition) Figure 16. 14 Some plants (eucalyptus) compete by chemical means. Clumps of shrubby Salvia plants (mint) are usually surrounded by bare zones separating the sage from neighboring grassy areas ( Figure 16. 15)

Australian ironwood trees

Consumers can influence the outcome of competition Keystone predator Starfish prey on mussels, barnacles, limpets, and chitons Remove starfish, what would happen? Species diversity increase or decrease? Why?

Grazing on plant diversity?

Predator can influence the outcome of prey competition Peter Morin, Rutgers Salamander Frog or toad tadpole (300 each of 3 species)

Apparent competition Combined populations of two prey species support a larger predator population neither can support alone. As a result, two prey populations reduced, gives outward appearance of interspecific competition. Experimental supports: Nettle aphid, grass aphid and ladybug beetle (Smith and Smith, page 359) Brought nettle aphid plants to grass aphid plants together suppressed both population, as a results of larger ladybug beetle population.

Apparent competition mediated by pathogens (microbes) Corals can be indirectly harmed by the presence of algae

Antibiotics can reverse the negative effects of algae on coral growth Smith et al. 2006

BIOL 4120: Principles of Ecology Lecture 14: Evolution of Species Interaction Dafeng Hui Office: Harned Hall 320 Phone: 963 -5777 Email: dhui@tnstate. edu

A story of European rabbits in Australia Invasive species and its control. Rabbit and myxoma virus.

Coevolution can occur between hostparasite, predator and prey and competitors n n n Predators exert a selective pressure on prey — any characteristic that enables individual prey to avoid being detected and captured by a predator will increase its fitness Natural selection should • Function to preserve “smarter, ” more evasive prey • Produce “smarter, ” more skilled predators Coevolution: as prey species evolve ways to avoid being caught, predators evolve more effective means to capture them

n n Coevolution is different from adaptation to environments Biological agent: n Stimulate mutual evolutionary responses in the traits of interacting populations n Predator and prey n Adaptations to environment have no reciprocal effect n Foster diversity of adaptations, rather than promote similarity n Avoid competition, predate on same prey etc n Adaptations to physical stress lead to same traits convergence.

Outline (Chapter 17) 14. 1 Adaptations in response to predation demonstrate selection by biological agents 14. 2 Antagonists evolve in response to each other 14. 3 Coevolution in plant-pathogen systems reveals genotype-genotype interactions 14. 4 Consumer and resource populations can achieve an evolutionary steady state 14. 5 Competitive ability responds to selection 14. 6 Coevolution involves mutual evolutionary responses by interacting populations

14. 1 Adaptations in response to predation demonstrate selection by biological agents n n n Coloration is an example of a trait that can evolve in prey under selection from predators Prey: use coloration to avoid predation Predators: can increase the fitness (adaptation) by increasing the efficiency to find well-camouflaged prey or avoid prey with coloration that signals noxious qualities

Crypsis versus warning coloration • Cryptic coloration (colors and patterns, object resemblance)) n Hide in normal environment • Moths on trees. Flounder • Most palatable, edible animals • Warning coloration or aposematism (bold colors with patterns that serve as warning to would-be predators) n Learnt behavior due to bad experience • Bees and wasps • Snake • Skunk (black and white stripes) • Noxious animals Why aren’t all potential prey noxious or unpalatable?

Many palatable organisms have evolved cryptic appearances to avoid detection by predators A Katydid, a stick insect, and a lantern fly

Mantid

Many unpalatable organisms have evolved warning coloration Aggregate to enhance the warning signal.

Mimicry Copy coloration of toxic species • Batesian mimicry Edible species mimic inedible species, non-venomous mimic venomous species Snakes • Mullerian mimicry Unrelated species have a shared color patterns that function to keep predators away Bumblebees, Social wasps Tropical butterfly

Batesian mimics are palatable prey organisms that resemble noxious ones Poisonous coral snake Scarlet king snake

Mullerian mimics are unpalatable species adopt a single pattern of warming coloration. Mantid (b) and moth (c) have both evolved to resemble a wasp (a).

Mullerian mimics are unpalatable organisms a pattern of warning coloration Warning coloration Mullerian mimicry Patterns of black and orange “tiger stripes” or black, red and yellow patterns serve as warning signals.

Predator Defenses Cryptic coloration, warning coloration, Mullerian mimicry, Batesian mimicry

n Predators may use cryptic coloration to blend into background and use deception by resemble the prey

14. 2 Antagonists evolve in response to each other n n Coevolution of pathogen and host by Charles Mode (1958) Pathogen virulence was controlled by V gene Host resistance was controlled by R gene Fitness of host and fitness of pathogen were each contingent on the genotype of the other

n n n Mode’s Conceptual Model: When host is susceptible (rr), selection favors virulent pathogens (VV or Vv) Virulent pathogens cause selection for host resistance (RR or Rr) When host is resistance, selection favors avirulent pathogen (vv) When pathogen is avirulent, selection favors susceptible hosts (rr) Cycling r(host)->V(pathogen)>R(host)->v (pathogen)->r(host)

Evolution in houseflies and their parasitoids David Pimentel et al. Cornell University (1960 s) One control population Not attacked by wasp One treatment population Attacked by wasp Train over three years Reproduction rate for wasp dropped from 135 to 39 progeny per female in the treatment cage, longevity decreased from 7 to 4 days. Then start experiment, allow population size changes

Pimentel’s classic experiment tested for a host evolutionary to a parasitoid Only wasp evolve, control Wasp: parasitoid, Both evolve, experiment Fly: host

Population changes in Pimentel’s parasitoid-host system demonstrated that populations evolve in response to each other

14. 3 Coevolution in plant-pathogen systems reveals genotype-genotype interactions Genetic basis of coevolution Crops and diseases Wheat and wheat rust Wheat rust (fungi): Many different strains Wheat: May be resistant or susceptible to a strain Genotype-genotype interaction: differences in the expression of genotypes in one species depending on the genotypes of another species.

Proportion of wheat rust strain populations in Canada (Green 1975)

Genetic variation in a host may parallel genetic variation in a pathogen Scale insects are sedentary and local populations evolve independently on individual trees (Alstad and Edmunds 1978)

14. 5 Competitive ability responds to selection Competitors exert selection pressure on each other 1. Diverge from one another in terms of the resources they consume 2. Selection for increased efficiency of resource use

Demonstrating genetic variation in competitive ability Francisco Ayala Two fruit fly species: Drosophila serrata and D. nebulosa Cage study in a lab Co-existence: 20 -30% D. serrata and 70 -80% D. nebulosa If remove D. serrata from these populations and put in a cage with unselected stocks of D. nebulosa, D. serrata showed superior competitive ability One general conclusion: Sparse population can evolve the ability to compete against other species more rapidly than dense populations.

Competiton study between fly populations David Pimentel House fly and blowfly Similar life cycle and food requirements Initially, each species won twice Using this facility, Pimentel showed that two species coexist for 70 weeks.

A rare competitor can evolve superior competitive ability A species that is being excluded by another species and becoming rare, can evolve increased interspecific competitive ability rapidly to regain control.

Character displacement Sympatric species: Two species coexist within the same geographic area Allopatric species: Two species’s geographic ranges do not overlap. If competition causes divergence, then the sympatric populations of species 1 and 2 in area B will differ more from each other than the allopatric populations of those speices in areas A and C: Character displacement.

Beak sizes of finches illustrate character displacement Darwin’s Finches Character displacement

Character displacement n The outcome of the competition was a shift in feeding niches. When the shift involves features of the species’ morphology, behavior, or physiology, it is called character displacement.

14. 6 Coevolution involves mutual evolutionary responses by interacting populations Coevolution implies reciprocal evolutionary responses between pairs of populations, as we see in predator-prey, pathogen-host. Pollinator and flower (humingbird and flower) Ants and aphids Aphids suck plant juices and produce large volumes of excreta from which they either do not or can’t extract all the nutrients. Thus honeydew production may simply reflect their diet, rather than having evolved to encourage protection by ants. Ants: voracious generalists and attack any insects they encounter. May not need special adaptations to deter the predators of aphids. Why don’t ants eat aphids they tend? (this restraint is an evolved trait of ants that facilitate ant-homopteran mutualism. )

Plant defenses and herbivore responses Amount of biomass eaten by herbivores: 6 -10% forest, 30 -50% grassland Outbreak of grasshopper, gypsy moths etc can kill. Normally not kill, even stimulate growth.

n n n n Plants defend themselves by producing secondary compounds Legumes (pea family) seeds contain SCs that inhibit the digestive enzymes of insect herbivores But adult bruchid beetles lay eggs on seedpods. Larvae can consume and grow Soybeans are resistant to attack even by bruchid species (produces chemicals that inhibit development of bruchid larvae) A tropical legume also contain a nonprotein amino acid that is toxic to most insect. But one bruchid can feed on the plants, possesses enzymes that degrade the amino acid. <Every defense, a new counterattack devised>

Yucca moth and yucca, an obligate mutualism Moth will lay eggs into the ovary of the flower, then crawls to the top of the pistil of the flower and deposits a bit of pollen on the stigma to make sure plant will Yucca, agave family produce Semelparous, huge flower seeds. Female also carry around pollens to other plants after lay eggs

Phylogenetic trees can reveal preadaptation (traits that become useful for a purpose other than for which they evolved)

Case study: Global Change Invasive plant species, the role of herbivores and Meta-Analysis Wide spread of invasive species: lack of natural enemies (no predators, parasites, pathogens) Results are not conclusive. John Parker, Georgia Tech Question: How native and introduced herbivores affect the abundance of native and introduced plants. Papers: 63 studies Herbivores: bison, deer, rabbits

One specific study of the herbivores: Pampas grass (an introduced species to CA) and native jackrabbits John Lambrinos, University of California Exclude rabbits decreased grass survival to 60%, allow grazing decreased the survival to 5%. Grazing of invasive species by native herbivores decreased survivorship.

What do the results of the metaanalysis tell us? 1. What invasive plant spp encounter matters (escape of native herbivores may be not a reason) 2. Native species survive better with native herbivores (co-evo) 3. Single study can’t reveal this information, as only native or invasive spp used.

The End

14. 4 Consumer and resource populations can achieve an evolutionary steady state Consumer and resource populations evolve continually in response to selection by their antagonists, what’s the end result of the interaction? Do evolution ever stop? Strict or diffuse relationships: one host (wheat-rust) or prey or multiple Evolve toward a steady state in which evolution continues

The End