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Home , Parasitism

Exploitation: , Herbivory, & Disease • Terms

Herbivore œ consume but usually do not kill them

Predator œ kill and consume other

Parasites œ live on the tissue of organisms, usually weakens them but does not usually kill them

Parasitoid œ usually kill their host, seen mostly in organisms with rapid life cycles ( and )

Pathogens œ induce disease in their hosts

1 Exploitation: Predation, Herbivory, Parasitism & Disease

• Parasites and That Manipulate Host Behavior

œ Parasites That Alter the Behavior of Hosts œ many parasites alter the behavior of the host to spread the parasite further

• Acanthocephalans (SpineyHeaded )

œ Infect amphipods

œ Alter amphipod behavior to make it more likely for them to be ingested by beaver, and muskrats

» Uninfected amphipods demonstrate negative phototaxis

» Infected organisms demonstrate positive phototaxis œ this brings them closer to the surface of the water and makes them more likely to be eaten

2 Exploitation: Predation, Herbivory, Parasitism & Disease

• Janice Moore (1983, 84) œ observed a complex relationship between three organisms:

œ An Acanthocephalan, Plagiorhynchus cylindricans

œ A terrestrial isopod, a pill bug Armadillidium vulgare, this serves as the intermediate host for Plagiorhynchus

œ The European , Sturnus vulgaris

Initial observations showed that only 1% of pill bugs were infected whereas 40 % of are infected œ from this she proposed that Plagiorhynchus alters the behavior of the pill bug to make it more likely to beingested œ via controlled experiments she found that in fact this was the case, the pill bug‘s behavior was altered in several ways:

œ Infected pill bugs spend less time in sheltered areas

œ Spend more time in high humidity environments on light colored backgrounds

3 Exploitation: Predation, Herbivory, Parasitism & Disease

4 Exploitation: Predation, Herbivory, Parasitism & Disease

5 Exploitation: Predation, Herbivory, Parasitism & Disease

• A that Mimics Flowers œ

Observation:

A Rocky Mt. Plant called Arabis exists for several years as a rosette then at some point bolts, producing flowers then seeds

Found That:

Arabis can be infected by a called Pucinia monoica which alters the life cycle of Arabis

Upon the rust invades meristematictissue causing it to grow atypically the next year

stem elongates leaves grow close together near the ends of the stem leaves take on a yellow color and resemble flowers of Rannunculus These yellow leaves attract many insects which in turn serve to spread the rust 6 Exploitation: Predation, Herbivory, Parasitism & Disease

7 Exploitation: Predation, Herbivory, Parasitism & Disease

• The Entangling of Exploitation with

œ Predation, Parasitism, and Competition in Populations of Tribolium (flour ) œ last chapter observed competition between T. castaneum and T. confusum dictated by temperature and humidity œ it has also been observed that a parasite, Adelina, can effect this relationship

8 Exploitation: Predation, Herbivory, Parasitism & Disease

• An Herbivorous Stream and Its Algal œ in many cases the exploiter greatly effects the population it is exploiting

œ Lamberti& Resh(1983) studied the larvae of a stream caddisfly, Helicopsyche • larvae forms a —portable house“ allowing it to feed upon and without being eaten itself • proposed that these larvae greatly effect the populations that it feeds upon because of this protection • reach densities of 4000 m2, this many individuals can greatly reduce their food supply

9 Exploitation: Predation, Herbivory, Parasitism & Disease

œ Experimental Design #1

• Unglazed tiles (15.2 cm x 7.6 cm) placed on the bottom of a creek

• Observed over a 7 week period

œ Colonization by algae

œ Invasion of Helicopsyche

10 Exploitation: Predation, Herbivory, Parasitism & Disease

• of algae and numbers of the caddisfly

11 Exploitation: Predation, Herbivory, Parasitism & Disease

œ Experimental Design #2

• Placed control tiles directly on stream bottom

• Placed experimental tiles 15 cm above the bottom, supported by a J œ rod that adults could not climb up and down to deposit

12 Exploitation: Predation, Herbivory, Parasitism & Disease

• Influence of elevating tiles on colonization by H. borealis

13 Exploitation: Predation, Herbivory, Parasitism & Disease

• Influence of excluding H. borealis on of bacteria and algae

14 Exploitation: Predation, Herbivory, Parasitism & Disease • An Introduced Cactus and Herbivorous Moth œ dramatic effects on populations can also occur in the absence of exploiters œ this is frequently the case with introduced œ The cactus ( stricta) introduced into Australia during the mid- 1800‘s • By 1930 covered 24 million hectares • An attempt to control these cacti was the introduction of a mothlarvae, Cactoblastis œ Larvae had two adverse affects on the cacti

» They fed on it directly

» Created wounds that permitted the entrance of killing pathogens

œ in 20 months the cactus population was reduced from 12,000/ha to 27/ha and a dynamic equilibrium was reached (as seen in nature)

A similar attempt is being utilized to try and control purple loosestrife and wooly adelgids

15 Exploitation: Predation, Herbivory, Parasitism & Disease

16 Exploitation: Predation, Herbivory, Parasitism & Disease

• A Pathogenic Parasite, a Predator and its Prey œ many ecological experiments are done at a small scale and interpolated up, on a few rare instances we have the ability to observe large scale, natural events

œ Sweden, Lindstrom (1994) œ discussed the relationship between a that caused in fox and the effect their decline had on hare populations

17 Exploitation: Predation, Herbivory, Parasitism & Disease

18 Exploitation: Predation, Herbivory, Parasitism & Disease

• Cycles of Abundance in Snowshoe Hare and Their Predators œ in many populations cycles of —boom and bust“ are observed, these can take place on a days to decades scale œ a classic study is one where data accumulated from the Hudson Bay Co. over a 200 yr. Period was used

19 Exploitation: Predation, Herbivory, Parasitism & Disease

20 Exploitation: Predation, Herbivory, Parasitism & Disease

œ Several explanations for these observations have been proposed:

• Elton (1924) œ variations were tied to sun spots œ MacLulichand Moran shot this down since they did not correspond

• Keith (1963) œ came up with — theories“ œ he stated that as the population grew:

œ Disease and parasitism increased

œ High densities resulted in physiological stress

œ Starvation resulted as food supply decreased

With further studies Keith found that food supplies and predators have a great affect

21 Exploitation: Predation, Herbivory, Parasitism & Disease

Food Supply

Hare require a great deal of food, during winter eat as much as 1500 g/day (typically 300 g/day) œ during this time biomass has decreased from 530 kg/ha in late November to 160 kg/ha by late March, frequently resulting in food shortages

Hare also affect their food œ heavy browsing causes them to produce turpenes and phenolicresins, hare find these substances distasteful œ the affects of this can last for up to 2 years œ some feel that this —triggers“ the 10 year cycle

Predators

Many other predators feed upon snowshoe hare: Goshawks, Great Horned Owls, Red Fox and Coyotes

22 Exploitation: Predation, Herbivory, Parasitism & Disease

• Experimental Tests of Food and Impacts

œ Performed detailed, long term experiments with snowshoe hares inan attempt to answer the question

• 8 years • 1 km2 blocks in undisturbed boreal forest; separated by 1 km • 3 controls, 6 experimental • Hares given unlimited food on 2 experimental blocks • 2 of the plots were fertilized, increasing food quality • Fenced in 2 plots, excluding mammalian predators but not , one received supplemental food (these were not replicated because ofintense demands of checking the fences, temps of -45o C

23 Exploitation: Predation, Herbivory, Parasitism & Disease

œ Results • Hares increased in all plots, followed by a decline

• Fertilizer did increase plant growth but not number of hares

• Hare numbers did increase, compared to controls on plots that:

œ Supplemented food (3x hare increase)

œ Predator reduction (2x hare increase)

œ Predator reduction + food supplementation (11x hare increase)

24 Exploitation: Predation, Herbivory, Parasitism & Disease • Population Cycles in Mathematical and Laboratory Models

œ Mathematical Models œ Lotaka/Volteraœ Volteraobserved that during WWI, when fishing was reduced, the number of increased while their prey decreased œ from this these two attempted to develop a model to reflect these trends œ in their model two major assumptions are required

• Host population increases exponentially

• Size of the population is limited by an exploiter

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26 Exploitation: Predation, Herbivory, Parasitism & Disease

Graphically these equations show a typical pattern showing reciprocal effects

27 Exploitation: Predation, Herbivory, Parasitism & Disease

œ Laboratory Models œ Utida(1957) set up an experiment using the Adzuki Bean Weevil and a œ these were grown in petridishes at 30o C and 75% RH

28 Exploitation: Predation, Herbivory, Parasitism & Disease

• Refuges and Host Persistence in Laboratory and Mathematical Models

œ Gause‘s Experiments

29 Exploitation: Predation, Herbivory, Parasitism & Disease

œ Huffaker(1958) used two mites, one served as the predator and the other as the prey œ he set up an environment using oranges, rubber balls, petroleum jelly and posts for —ballooning“ œ the mites demonstrated slightly different dispersal behavior

• Eotertranychus sexmaculatus moved either by crawling or ballooning

• Typhlodromus occidentalis moved by crawling only

30 HUFFAKER’S MITES Making it easier for the prey to escape and harder for the predator to follow.

Vaseline lines slow predator movements between oranges.

Wooden pegs speed prey movements. They climb up the pole and produce a silk strand then are dispersed by air movements. 31 Exploitation: Predation, Herbivory, Parasitism & Disease

This concept of refuges is incorporated in Lotka-Voltera’s equations as p – it now should be realized how ever that its value although constant in a given environm ent can be different in different 32 Exploitation: Predation, Herbivory, Parasitism & Disease

• The Variety of Refuges

œ Space œ burrows, , air, H20, others can be more subtle

Example: - The example of Opuntia being affected by an insect and a pathogen did not result in of cactus, although it didgreatly decrease it numbers œ several reasons:

hard for insects to find isolated cacti

insects don‘t attack cacti growing on nutrient poor soils, food of too poor a quality

some cacti grow at altitudes on or above 600-900m, too cold for the insects to exist

33 Exploitation: Predation, Herbivory, Parasitism & Disease

œ Protection By Numbers œ large numbers of organisms can serve as a refuge in several ways

• Large groups intimidate

• Decreased probability of any one individual being eaten (dependent upon density)

• Predators demonstrate a combined response being both functional and numerical

œ Prey Consumed/Predator X Predators/Area = Prey Consumed/Area

• As prey density increases the percentage of prey consumed decreases

34 Exploitation: Predation, Herbivory, Parasitism & Disease

35 Exploitation: Predation, Herbivory, Parasitism & Disease

œ by an Australian œ Masting- Eucalyptus produce seeds every year but they remain on the tree until fire causes their release

36 Exploitation: Predation, Herbivory, Parasitism & Disease

œ Predator Satiation by Periodical Cicadas œ Magicicada emerge every 13 yrs. in the south and 17 yrs. in the north œ these periodic booms in population can be extraordinary œ 4 million/ha which equates to 1,900 œ 3,700 kg/ha **highest biomass production of terrestrial ever recorded.

37 Exploitation: Predation, Herbivory, Parasitism & Disease

œ Size as a Refuge

38 Exploitation: Predation, Herbivory, Parasitism & Disease

• Individual size

• Projection of a larger size

• Grouping to appear bigger

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