Ecology Life History and Intraspecific Competition

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Unformatted text preview: Life History Strategies Life To the uninitiated, nothing could be To worse than accompanying a bunch of “birders” on a field trip. They keep stopping, peering through their binoculars, whispering to each other, and motioning you to keep quiet. Why are they so fascinated with birds? Aren’t they all pretty much the same? Life History Strategies Life Of course, not. Of Even the most naïve non-biologist knows that birds come in an amazing variety of colors and sizes and amateur birders are legion. Life History Strategies Life Of course, not. Even the most naïve Of non-biologist knows that birds come in an amazing variety of colors and sizes and amateur birders are legion. Life History Strategies Life What we are interested in exploring What here is the variety and potential adaptive value of life histories found in all groups of organisms. Life History Strategies Life Since ornithologists such as David Since Lack have contributed so much to our understanding of life histories, we begin by using birds to illustrate the complexity and diversity of life histories. These accounts are mostly based on These Janzen (1983). Janzen The Groove-billed Ani (Crotophaga sulcirostris) 1. 1. The Groove-billed Ani (Crotophaga sulcirostris) is a common and conspicuous bird found in the lowlands and mid-elevations of Central America. Females are about 65 g in mass, but lay extremely large 11 g eggs. Since each female may deposit 4-8 eggs in the nest, the combined total mass of her eggs may exceed her body exceed weight! What is more extraordinary, however, is that this species engages in a communal breeding system. The Groove-billed Ani (Crotophaga sulcirostris) The Groove-billed Ani (Crotophaga sulcirostris) The birds live and breed in a group ranging from The 2-8 adults, with an equal number of males and females. The group defends a common territory, year-round. A single nest is constructed and all females deposit their eggs in it, forming a communal clutch. All members of the group contribute to incubation and feeding of the nestlings. Anis are highly social, roosting and sleeping in close contact with each other while engaging in mutual grooming. The Groove-billed Ani (Crotophaga sulcirostris) However, Vehrencamp (1977, 1978) found that However, there are specific costs and benefits to the individuals participating in this group endeavor. For example, there are individual differences in the number of eggs that get into the nest, in number the amount of time and effort put into amount incubation, and in the care of the nestlings. care Furthermore, the eggs and offspring of the dominant females and males benefit the most. The Groove-billed Ani (Crotophaga sulcirostris) Dominant females lay their eggs last Dominant and actually remove eggs laid by other females from the nest. These dominant females then behave like brood parasites in that they actually put less effort into incubation and feeding than do the subordinate females. The Groove-billed Ani (Crotophaga sulcirostris) On the other hand, so-called alpha On males, who have the most eggs in the nest (and the most to lose), perform a large share of the incubation. The Groove-billed Ani (Crotophaga sulcirostris) What is the advantage of communal What nesting, especially for the subordinate birds? How do the dominant females get How away with dumping the subordinates’ eggs while they do less of the work? eggs The Northern Jacana (Jacana spinosa) 2. 2. The Northern Jacana is found from The Costa Rica northward in Central America wherever there is floating aquatic vegetation. Jacanas have reversed the usual roles of the genders. Males build the nests and incubate and care for the young. The Northern Jacana The The Northern Jacana (Jacana spinosa) Females lay one egg a day for four Females days in a typical clutch. Females are able to lay a second clutch of eggs elsewhere within 7 to 10 days, if necessary. The eggs are quite small (7.9 g) as compared with the average weight of the females (160.9 g). Males are smaller (mean weight of 91.4 g) than females. The Northern Jacana (Jacana spinosa) The mating system is polyandrous. Each The polyandrous Each male defends a small territory while each female defends a territory containing one to four males. Once chicks reach 12-16 weeks of age the females often provide a second clutch for the males to care for. The ratio of males to females varies seasonally and from place to place, but is often skewed in favor of the males. The Northern Jacana (Jacana spinosa) For example, the long-term average at For Turrialba, Costa Rica was 2.3 males per female (Jenni 1983). Jacanas have a very high reproductive potential, but the hatching and fledging survivorship rates are very low. The Frigate bird (Fregata magnificens) 3. 3. The Frigate bird (Fregata magnificens) iis a s large (800-1700 g) seabird with a life history that is unusual because of its low reproductive potential. Both sexes do not become mature until 5 to 8 years of age. Females breed only every other year and lay one egg in a clutch. The egg takes 55 days for incubation and the nestlings grow very slowly. They are fed primarily by the females for as long as 14 months. The Frigate bird (Fregata magnificens) The Frigate bird (Fregata magnificens) Given a 50:50 sex ratio, a new female is Given produced, on average, only every four years! The potential r-value for this species is extremely low, but by contrast survivorship of adults is very high. The life span is 40 or more years. What selective pressures resulted in a life What history so radically different from that of most bird species? most Brown Pelican (Pelecanus occidentalis) 4. 4. Brown pelicans (Pelecanus occidentalis) are one of the best known birds in the Western Hemisphere. They are found on both the Atlantic and Pacific coasts from North Carolina to Brazil and from British Columbia to Chile. Breeding colonies may contain as many as 500 pairs. An adult brown pelican weighs from 2-5 kg; it takes 3-5 years to attain adult plumage. Brown Pelican (Pelecanus occidentalis) Brown Pelican (Pelecanus occidentalis) Males and females share chick-raising Males duties equally, and the normal clutch size is 3 eggs. Incubation takes 30 days and the nestlings need 10-12 weeks to fledge. Schreiber and McCoy (1983) visited a pelican colony four times during the breeding season of 1979 on Isla Guayabo in Costa Rica. Of 430 nests surveyed, most had 3 eggs, but the average was 2.42. Brown Pelican Brown (Pelecanus occidentalis) By their fourth visit the number of By surviving fledglings was 506, which was an average of 1.18 per nest. The Brown pelican is much larger than the Frigate bird, has a much higher reproductive potential, but also has a lower survival rate. lower Oropendola Oropendola (Zarhynchus wagleri) 5. Oropendolas (Zarhynchus wagleri), which which are related to blackbirds and orioles, nest in colonies. Males weigh twice as much as females (212 g versus 110 g) and they have been shown to take twice the energy to fledge as opposed to a female. As a result, male mortality among chicks is much higher during times of food scarcity. much Oropendola Oropendola (Zarhynchus wagleri) Oropendola Oropendola (Zarhynchus wagleri) The sex ratio at colonies is normally The 5:1 in favor of females. In Costa Rica, nesting begins with the dry season (December) and three complete breeding cycles are possible before the beginning of the rainy season in May. The normal clutch size is two, but breeding success is very low. Oropendola Oropendola (Zarhynchus wagleri) The average number of chicks fledged The per nest is 0.40. On the other hand, survivorship of adults is very high. Adults have been recorded living beyond the age of 26 in the field. By contrast to frigate birds, which also have very long adult life spans, this species has a much higher reproductive potential. Oropendola Oropendola (Zarhynchus wagleri) http://www.youtube.com/watch?v=Hkghd7J3ezI Orange-collared manakin (Manacus aurantiacus) http://www.youtube.com/watch?v=T2Bsu4z9Y3k Nightjars and Nighthawks Found in woodlands and open country Become active at twilight and feed on insects. The Pauraque is very common at night along roads and paths at Palo Verde, Costa Rica. Its call is very common. Pauraque http://ibc.lynxeds.com/video/pauraque­nyctidromus­albicollis/bird­was­sitting­along­ro Great Pootoo The Great Potoo is very unusual looking and somewhat owl-like. During the day they look like dead branches. At night they prey on large insects, small birds and lizards. They do not build nests, but females lay a single egg in the crevice on a stump or large branch. Rarely seen, they are recognized by their amazing mournful cries. Great Pootoo Animals ARE Interesting! http://www.youtube.com/watch?v=­ssXJtzFOjA Life History Strategies Life So what have we learned about life So histories from these birds? 1. 1. 2. 2. 3. 3. Nesting ranges from communal to Nesting colonial to pair-wise. Breeding systems vary from communal Breeding to polyandrous to simple pair bonds. Fecundity vary from one egg every other Fecundity year to as many as eight in one clutch. Life History Strategies Life 4. Survivorship of the chicks is as low as Survivorship only 0.40 per nest, but adult survivorship is as high as 40 years. What accounts for all this variation in life What histories? Under what conditions do we find high versus low fecundity and/or survivorship? These are questions we want to attack in this chapter. want Life History Strategies Life Another set of questions we wish to Another address concerns the relationship between the body size of an organism and its reproductive potential. Although body mass does not determine all aspects of life history it is a powerful influence. For example, Figure 6.1 is based on data for 24 species of mammals found in Costa Rica. mammals Figure 6.1. Log length of the pre-reproductive period versus log of mass in 24 species of Costa Rican mammals. Data from Janzen 1983. Note that the slope is close to the predicted value of 0.25. Linear regression is significantly positive. Linear Length of Pre-reproductive period 5 4 3 2 1 0 0 1 2 3 Log Mass 4 5 6 Life History Strategies Life The obvious conclusion is that there is a The higher likelihood of delay in reproductive maturity in the larger animals. Similarly, Figure 6.2 demonstrates that Similarly, animals with larger mass also have a longer interval between births. Litter size and total reproductive output per Litter year were negatively associated with body mass, though the relationships were weak in this set of data. 3 Intervl between births in years 2.5 2 1.5 1 0.5 0 0.5 1.5 2.5 3.5 Log Mass 4.5 5.5 Life History Strategies Life We have known the basics of demography We since the 1920s, but only in 1954 did ecologists begin to systematically begin to examine the diversity of life histories. examine We know that this relationship exists: r = lnRo/G Where G = Generation Time Life History Strategies Life If two of these variables are known, If the third can be determined, as least for a population with a stable age distribution. However, there is no necessary relationship among all three of these variables. three Life History Strategies Life The three variables are: 1) increase per unit time (r) 2) the increase per generation (R0) 3) generation time (G) Life History Strategies Life We know that: 1. r is inversely related to G, is generation time, and generation 2. generation time is directly related to generation size (length or usually mass). mass Figure from: Bonner, J.T. 2006. Matters of Size. Natural History. 115(9): 54-59. 115(9): Life History Strategies Life It follows that: 3. r is inversely related to size (mass). 1. Life span and growth rate are Life negatively associated (Stearns 1992). 1992). Life History Strategies Life 5. High individual growth rates are High positively correlated with r. positively 6. Growth rate is inversely related to Growth body mass. body Life History Strategies Life In summary, small size is associated with: In small 1. 2. 2. 3. 3. fast growth rates, fast high r-values and high short generation times. Large mass is associated with: 1. 2. 2. 3. 3. slow growth rates, slow small r-values and small llong generation times. ong Life History Strategies Life Are these relationships inevitable? We know that mass determines a We mass great deal about an organism. great Mass is inversely related to metabolic Mass rate, and a large number of metabolic functions. functions. Life History Strategies Life Mass is also negatively associated Mass with the intrinsic rate of increase (r). with But mass is positively associated with But generation time, length of life and length of maturation time. length Life History Strategies Life There exists a basic “allometric” equation applicable to both the metabolism and the life history of an organism. This means some variable is changing as size or mass changes. is Life History Strategies Life This equation is well known to physiologists This but is becoming of interest to ecologists. but Y = Y0Mb log Y = log Y0 + b log M Y iis a dependent variable such as metabolic s rate or generation time. rate Y0 is a constant, M is mass and b is a scaling exponent. scaling Life History Strategies Life What is of interest to both What physiologists and ecologists is the tendency for the exponent b to equal some multiple of 0.25. some Life History Strategies Life Going back to the log of the length of Going the pre-reproductive period versus log of mass for 24 species of Costa Rican mammals. The slope = 0.27. mammals. The second figure is the log of interval The between births in years for the same group of mammals. The slope = 0.25. group Length of Pre-reproductive period 5 4 3 2 1 0 0 1 2 3 Log Mass 4 5 6 3 Intervl between births in years 2.5 2 1.5 1 0.5 0 0.5 1.5 2.5 3.5 Log Mass 4.5 5.5 Life History Strategies Life In the next figure we have the In allometric scaling of metabolic rate for allometric organisms ranging from unicellular Protista to homeothermic mammals. The regression lines all have a slope The of 0.75 (a multiple of 0.25). of Life History Strategies Life What we can conclude from all of this What is that mass is a powerful determinant mass of many things, from metabolic rate to life history strategies. life Life History Strategies Life In 1954, an In ecologist, L.C. Cole, investigated life histories. He was He interested in three problems. three Iteroparity versus Semelparity Iteroparity 1. What is the selective advantage of What iteroparity? That is, repeated iteroparity That breeding by long-lived adults. breeding As opposed to semelparity, breeding As semelparity once and then dying. once Iteroparity versus Semelparity Iteroparity Semelparity versus iteroparity is one of the iteroparity most significant differences in life histories among all organisms. organisms. The nautilus is the only living iteroparous spawner among the cephalopods, a mature female nautilus is capable of spawning once every year. Life History Strategies Life 2. What aspect of a life history has the What greatest effect on the r-value of an organism? organism? A. litter or clutch size versus litter B. the length of the pre-reproductive B. the period. period. Life History Strategies Life First, Cole discovered that iteroparity First, iteroparity is of greatest value to organisms when the survivorship of the offspring is uncertain. If, in a given year, all of the offspring may not survive, but adult survivorship is high, there is powerful selection for an iteroparous life history. life Life History Strategies Life Second, he found that Second, the length of the prelength reproductive period had a much greater effect on r than did simple litter size. simple Dragonflies have a long pre-reproductive period. Life History Strategies Life That is, by shortening That the generation time, an organism increases its r-value much more than if it simply increases its litter size. litter Arabidopsis thaliana ideal for study with a short generation time (5 weeks) and a high seed number per plant (10,000). Example Example Four fertility scenarios demonstrating Four the importance of early reproduction early on the value of r. lx = survivorship mx = fertility GRR = Gross Reproductive Rate R0 = Net Reproductive Rate G = Generation Time r = intrinsic rate of increase Age Age lx scenario scenario 1 2 mx mx scenario 3 mx scenario 4 mx 0 1.000 0 0 0 0 1 0.100 0 0 0 0 2 0.050 20 10 0 0 3 0.025 10 30 40 50 4 0.010 0 0 0 0 5 0 0 0 0 0 GRR 30 40 40 50 R0 1.25 1.25 1.00 1.25 Age Age lx scenario scenario scenario scenario 1 2 mx mx scenario 3 mx scenario 4 mx 0 1.000 0 0 0 0 1 0.100 0 0 0 0 2 0.050 20 10 0 0 3 0.025 10 30 40 50 4 0.010 0 0 0 0 5 0 0 0 0 0 G 2.2 2.6 3.0 3.0 r 0.102 0.086 0.000 0.074 Theory of r- and K-selection Theory MacArthur and Wilson (1967). They theorized that colonizing species They would have different life histories from species found late in mature ecosystems. ecosystems. Theory of r- and K-selection Theory For colonizing species the major For components of fitness include: components 1. Arriving first in an open habitat; Arriving meaning having a high dispersal rate. meaning The ability to grow quickly once at a The suitable site. 2. Theory of r- and K-selection Theory 3. The ability to reproduce quickly. Therefore, arriving, quickly harvesting Therefore, resources and reproducing, even if using the resource inefficiently, were selected for in this r-selecting environment. environment. Theory of r- and K-selection Theory On the other hand, in crowded On environments selection favors the efficient use of resources, the ability to survive when resources are scarce and the ability to compete. and This was termed a K-selecting This environment. Theory of r- and K-selection Theory There appears to be a tradeoff in life There histories between competition and colonizing ability. colonizing K-selected species are excellent competitors but poor colonizers. competitors r-selected species are excellent r-selected colonizers but poor competitors. colonizers Theory of r- and K-selection Theory What are these r- and What K-selected traits? In what environments In would you find them? would Comparison of Two Vole Species Regarding Relative K-Selectedness Microtus pennsylvanicus M. breweri Length of Life 0 +1 Body Size 0 +1 Age at First Reproduction 0 +1 Development Rate +1 0 Litter Size 0 +1 Parental Care 0 +1 Overt Agression 0 +1 +1 +6 Total Note: The more K­selected species is given +1 and the less K­selected species 0. Examining r- and K-selection in Seed Sizes in Seeds range over 10 orders of Seeds magnitude. magnitude. Saprophytic and parasitic seeds = 10-6 g Herbs and grasses = 10-5 to 10-2 g Examining r- and K-selection in Seed Sizes in 2 Shrubs and trees from 10--2 to 104 g. to g. The largest seed belongs to a coconut The palm. palm. Seeds are units of dispersal but also Seeds reflect the competitive ability of the seedling. seedling. Seed Size Seed Size Correlations Seed Environmental Factor Usual Seed Size Early Successional Early Stages Stages Small Seeds Late Successional Late Stages Stages Large Seeds Herbaceous Annuals and Small Seeds Herbaceous Perennials Perennials Shrubs and Trees Large Seeds Dispersal Ability Small Seeds Seed Size Correlations Seed Environmental Factor Usual Seed Size Competitive Ability Large Seeds Early Germination Small Seeds High Altitude Small Seeds Short Growing Season Small Seeds Shade/Low Light Shade/Low Availability Availability Large Seeds Seed Size Correlations Seed Environmental Factor Usual Seed Size Low Moisture Low Availability Availability Large Seeds! Desert Conditions Large Seeds! Why? r- and K-selection rtheory not operative theory The physical The environment is the major selective factor. major Not colonizing ability. Not competitive Not ability. ability. Examining r and K-selection Examining Other major selective factors for life histories Other include predation and unpredictable environments. environments. If predators prey mainly on young age If classes or there is no predation, life history often has a “K-selected syndrome”. often If predators prey mainly on adults, the result If is an “r-selected syndrome”. is Examining r and K-selection Examining Take Home Lesson: Use the theory of r- and K-selection Use cautiously when evaluating life histories. histories. Life histories may result from a Life multitude of selective factors. multitude Predation and Life Histories Predation Predation also plays a role in the Predation shaping of life histories. Studies by Reznick and Endler (1982) Studies and Reznick et al. (1997) on guppies have confirmed the effect of predation on life histories. Reznick and Endler (1982) came to Reznick the following conclusions: Predation and Life Histories Predation 1. When a predator prefers mature fish, When the guppies devote a high percentage of their body weight to reproduction, there are short inter-brood intervals, and they mature at a small size (“fast” life cycle). life Predation and Life Histories Predation 2. When a predator prefers immature When stages or no predators are present, the guppies devote a low percentage of body weight to reproduction, there are long inter-brood intervals, and they mature at a large size (“slow” life cycle). cycle). Predation and Life Histories Predation In an experimental test of their In predictions, Reznick et al. (1997) compared the life histories of two populations of guppies (Poecilia populations Poecilia reticulata) lliving in upstream versus reticulata iving downstream habitats. The upstream habitats lacked several The species of fish, many of which prey upon adult guppies, which were present downstream. present Predation and Life Histories Predation The upstream, low-predation The population had later sexual maturity, lower fecundity, less frequent litters, and larger offspring as compared with the high-predation, downstream population. In other words, lack of predation In produced the suite of traits listed under point two above. point Predation and Life Histories Predation If we knew nothing about predation, If we might conclude that such traits were consistent with the K-selection (or slow) syndrome, and that these life histories were shaped by competitive interactions. Predation and Life Histories Predation In a transplant experiment, Reznick et In al. (1997) moved guppies from the high predation to the low predation habitat. After eleven years the transplanted After guppies had evolved life histories similar to the resident populations. Predation and Life Histories Predation In a similar study, Crowl and Covich In (1990) showed that freshwater snails (Physella virgata virgata) also shift also their life history characteristics when exposed to their major predator, the crayfish, Orconectes virilis. Orconectes Predation and Life Histories Predation When exposed to water-borne cues When released when crayfish fed on other members of the population, the snails exhibited rapid growth and delayed reproduction until they reached a size of 10 mm after eight months. In the absence of the cue, snails In typically grew to about 4 mm in 3.5 months and then began reproduction. months Predation and Life Histories Predation Since crayfish selectively prey on the Since smallest individuals, juvenile mortality is high. By delaying the onset of reproduction By and growing to a larger size, snails decrease mortality from size-specific predation. predation. Predation and Life Histories Predation In both of these studies, when In predators concentrated their efforts on immature or smaller stages, the life history of the prey species shifts to a “K-selected” syndrome. Obviously, caution must be used when Obviously, evaluating the potential causes of a particular life history. particular Disease and Life Histories Disease In fact, disease may have a similar In effect. Tasmanian devil populations have Tasmanian been declining since 1996 because of a contagious form of cancer known as facial tumor disease. Disease and Life Histories Disease This disease causes death between This the ages of two and three years. Recent data suggest that Tasmanian Recent devils are now breeding at a younger age. In the past devils began breeding In between the ages of two and four between Disease and Life Histories Disease Disease and Life Histories Disease But now, there has been a 16-fold But increase in breeding at the age of one (Jones et al. 2008). Not only that, but the cancer has Not fundamentally changed the life history from one of iteroparity to one of iteroparity semelparity (reproducing only once in semelparity a life time). life Whales and Hunting There has been a change in the size of Antarctic minke whales (Balaenoptera bonaerensis) at sexual maturity over the last several years. Whales and Hunting There are several hypotheses that might explain this observation: 1. 2. 3. Intraspecific competition with other baleen whales. Massive increase in krill population numbers. Over-fishing by Japanese whalers. References References Jones, M.E., A. Cockburn, R. Hamede, C. Hawkins, H. Jones, Hesterman, S. Lachish, D. Mann, H. McCallum, and D. Pemberton. 2008. Life history change in disease-ravaged Tasmanian devil populations. Proceedings of the National Academy of Science 105: 10023-27. Academy Luksenburg, J. A. and E. C. M. Parsons. 2009. The ‘krill Luksenburg, surplus’ hypothesis and the shift in age at sexual maturity in the Antarctic minke whale (Balaenoptera bonaerensis): A the ): retrospective salute. Poster presentation at the International Marine Conservation Congress, George Mason University, May 17 – 24, 2009. May Intraspecific Competition Intraspecific Competition: “A biological interaction Competition: between two or more individuals for a resource in short supply.” resource Resource: “A substance or factor that Resource: leads to an increase in fitness as its availability in the environment is increased; and which is consumed by consumed the organisms.” the Intraspecific Competition Intraspecific Characteristics: 1. 2. 3. The interaction is reciprocally The negative. negative. The ultimate effect is a decreased The contribution to the next generation. contribution The resource for which they are The competing must be in short supply. competing Intraspecific Competition Intraspecific Types of Competition 1. 2. Intraspecific: within a species Interspecific: between species Modes of Competition 1. Resource or Depletion Competition: Simple removal of the resource without active interference with other individuals. Finding and consuming the resource first. Finding Intraspecific Competition Intraspecific 2. Interference Competition: An An individual actively blocks access to a resource through behavioral, chemical or other means. chemical Includes territoriality and guarding Includes behavior. Defense of an area containing resources or the resource itself. itself. Intraspecific Competition Intraspecific Includes Includes allelopathy among allelopathy plants. That is the secretion of chemicals to inhibit growth or germination of other plants. other Tree of Heaven (Ailanthus altissima) Intraspecific Competition Intraspecific 1. 2. 3. 4. 5. The effects of intraspecific competition can The be classified as: be Increase in mortality Decrease in fertility Reduced size of adults Reduced growth rates (longer development Reduced time) time) Male-male and male-female behaviors Male-male during reproduction during Recruitment of elk calves in Yellowstone National Park as a function of adult population size in the previous year (based on Houston 1982) (based Number of females with calves 0.6 0.5 0.4 0.3 y = -0.03x + 0.55 R2 = 0.62 0.2 0.1 0 3 5 7 9 11 Elk population in previous year (in thousands) 13 Birth rate of the American bison (Bison bison) as a Birth function of population size (Based on Gross et al. 1973) function Number of births per female 1 0.8 0.6 0.4 0.2 0 0 100 200 300 400 Population size 500 600 700 Eggs produced per female beetle/day Fertility versus density in Rhizopertha dominica dominica 10 8 6 4 2 0 1 6 11 16 21 26 Density per gram of wheat 31 36 Percent survival of first-instar larvae to adult Survivorship of the grain beetle, Rhizopertha dominica, versus initial density of first-instar dominica versus larvae larvae 100 80 60 40 20 0 1 2 3 4 5 6 Initial density per grain of wheat 7 8 Law of the Final Constant Yield Yield Agricultural or plant yield per unit area Agricultural yield will increase with density up to a maximum or final yield. Thereafter, increasing density leads to Thereafter, an increase in mortality (“thinning”) and a reduction in the average size per plant. plant. Law of the Final Constant Yield Yield C = Dw Where: C = final constant yield in kilograms per area D = density of plants w = mean weight per plant Taking logs we have: Taking logC = logD + logw logC Law of the Final Constant Yield Yield Or: log w = log C – log D Or: log And finally: log w = (-1) log D + log C log If we use density as the independent variable, If then we have an equation with log w as the dependent variable. This is an equation for a straight line with log C This as the y-intercept and -1 as the slope. as Law of the Final Constant Yield Yield Again, what we expect with an Again, increase in density is that yield will level off at a constant, while the average size per plant decreases. In a perfect world the slope of this line In would be -1.0. But it is usually closer to -0.6 in the experiment we do in lab. (Even lower this year!) (Even Law of the Final Constant Yield Yield Log Density of Surviving Plants Log Mass/Plant Intraspecific Competition Data Fall 2010 4.000 3.500 3.000 2.500 2.000 1.500 y = -0.121x + 2.8826 1.000 R2 = 0.0188 0.500 0.000 0.000 0.200 0.400 0.600 0.800 1.000 1.200 1.400 1.600 1.800 2.000 Log Survivors Log of Survivors vs. Log of Mass per Pot Spring 2009 1.40 1.20 Log of Mass per Pot 1.00 0.80 0.60 0.40 y = 0.784Ln(x) + 0.629 R2 = 0.8662 0.20 0.00 0.00 0.50 1.00 Log of Survivors 1.50 2.00 Intraspecific Competition Intraspecific 3. Reduced size of adults. 4. Reduced growth rates (longer Reduced development time). development Rana tegrina – frog tadpoles or polywogs Male-Male Competition Male-Male Male-Female Competition Examples: Dung beetles Dung (male-male competition) competition) Dunnocks Dunnocks (male-female competition) competition) Male-Females Competition in Dunnocks Dunnocks Mating combinations: Monogamy: one male with one female Polygyny: one male with two or more one females females Polyandry: one female with two or more one males males Polygynandry: multiple males and multiple females females Dunnock Mating http://www.youtube.com/watch?v=hjEt­Z_NMMw Questions? ...
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