**Study Guide for Ecology EXAM 2**

Bateman's work and fruit flies

Bateman's Principle There is a basic asymmetry in sexually reproducing organisms: a female's reproductive success depends on her ability to make eggs large female gametes require considerable resources the female's ability to gather resources determines her fecundity a male's reproductive success depends on the number of eggs he can fertilize: small male gametes require few resources the male's ability to mate with many females determines his fecundity lecture 12!

limitation types

Density-independent limitations Density independent: factors that limit population size regardless of the population's density. Common factors include climactic events (e.g., tornadoes, floods, extreme temperatures, and droughts). Example: The apple thrip was a common insect pest in Australia that would undergo large population fluctuations. Researchers predicted that these fluctuations were due to seasonal fluctuations in temperature. Their predictions (dotted line) matched closely with actual abundances (bars). 2 Density-dependent limitations Density dependent: factors that affect population size in relation to the population's density. Negative density dependence: when the rate of population growth decreases as population density increases. The most common factors that cause negative density dependence are limiting resources (e.g., food, nesting sites, physical space). As a population's size increases, resources are divided among more individuals, and per capita resources decline to a level at which individuals find it difficult to grow and reproduce. Crowded populations can also generate stress, transmit disease, and attract predators. 2 Density-dependence in animals Examples: Raymond Pearl introduced different densities of fruit flies into bottles with identical amounts of food. As fly numbers increased, competition for food became more intense and adults had fewer progeny and shorter lifespan. In the 1970s, common terns began to colonize Bird Island in Massachusetts. When nest sites became limiting, the population stopped growing and birds began colonizing nearby Ram Island. When nest sites on Ram Island became limiting, they colonized Penikese Island. 2 Density-dependence in plants When plants are grown at high densities, each plant has access to fewer resources such as sunlight, water, and soil nutrients. Example: Horseweed plants were sown at a density of 100,000 per m2. Over time, many individuals died, leading to a hundredfold decrease in density. As density decreased, there was a thousandfold increase in the weight of surviving individuals. Self-thinning curve: a graphical relationship that shows how decreases in population density over time lead to increases in the size of each individual in the population; often has a slope of . 2 Density-dependent limitations Positive density dependence: when the rate of population growth increases as population density increases (also known as inverse density dependence, or Allee effect). Positive density dependence typically occurs when population densities are low, which may make it hard to find mates, particularly when sex ratios are uneven. Low densities can also lead to harmful effects of inbreeding and a higher predation risk. Example: Populations of cowslip with fewer than 100 individuals produced fewer seeds per plant than larger populations. 2 Density-dependent limitations Populations are often regulated by both positive and negative density dependence. Increased densities provide more individuals for breeding. Above some density, resources become limiting and negative density dependence begins to play a role. Example: Herring experience low population growth at low population densities, high population growth at intermediate densities, and low population growth at high densities. ____ Overshoots and die-offs Populations in nature rarely follow a smooth approach to their carrying capacity. Overshoot: when a population grows beyond its carrying capacity; often occurs when the carrying capacity of a habitat decreases from one year to next (e.g., because less resources are produced). Die-off: a substantial decline in density that typically goes well below the carrying capacity. Die-offs often occur when a population overshoots its carrying capacity.

Logistic growth model

A growth model that describes a population whose growth is initially exponential, but slows as the population approaches the carrying capacity of the environment.

Definition of breeding system

A mating system is a way in which a group is structured in relation to sexual behaviour. >>> mating systems include 1.monogamy, 2. polygamy (which includes polygyny, polyandry, and polygynandry), and promiscuity.

Population Regulation

A pattern of population growth in which one or more density-dependent factors increase population size when numbers are low and decrease population size when numbers are high.

Life tables

Age-specific summaries of survival patterns of a population. ***** listing of survivals and deaths in a population in a particular time period and predictions of how long, on average, an individual of a given age will live

The cost of meiosis

As compared to species that reproduce asexually, individuals of diploid species that reproduce sexually pass on only 1/2 of their genetic material to their offspring. This is referred to as the "cost of meiosis"

Comparing growth models Exponential and geometric growth models are identical

Comparing growth models Exponential and geometric growth models are identical, except er takes the place of λ. Hence, When a population is decreasing, λ < 1 and r < 0. When a population is constant, λ = 1 and r = 0. When a population is increasing, λ > 1 and r > 0. Differences between the two models 1. Continuous model is used for organisms that have "year around" reproduction (i.e. humans). 2. Geometric model is used for organisms that reproduce during discrete breeding seasons. 3. To calculate a future population size with the continuous model, one must use the derivative of the equation (Nt=No ert). Under what circumstances does one see exponential growth? 1. When per-capita resources are abundant 2. When predators are absent (i.e. introduced species, "weedy" species) We know that super-abundant resources do not occur forever, so why study exponential growth? 1. All populations have the potential for exponential growth - when populations don't follow exp. growth, can ask why 2. These models recognize the multiplicative nature of population growth & the positive feedback that gives populations the potential to increase at an accelerating rate We know that super-abundant resources do not occur forever, so why study exponential growth? 3. No population increases exponentially forever, but some do for limited time - insect outbreaks, diseases, weedy plants All Exponential growth is temporary! Population Structure and Growth Population Regulation Limits on growth Population growth can be limited by both density-independent and density-dependent factors Density-independent factors (often abiotic) influence population size independent of population density Density-dependent factors are factors that cause resources to become limiting and are related to population size

Costs and benefits of sexual reproduction

Costs of sexual reproduction Sexual organs require considerable energy and resources. Mating behaviors (e.g., floral displays, courtship rituals) require time and energy, and increase risk of herbivory, predation, and parasitism. Asexual Sexual Cost of meiosis: the 50% reduction in the number of a parent's genes passed on to the next generation via sexual reproduction versus asexual production; occurs because sexual genes are haploid. _______ The cost of meiosis can be counterbalanced by hermaphroditism, which is when an individual possesses both male and female gametes. Individuals can contribute one set of genes to offspring via female function and one set via male function. Costs of sexual reproduction can also be offset if the male helps the female take care of offspring, reducing female energy costs. ________ Benefits of sexual reproduction Purging mutations: Sexually reproducing organisms can lose deleterious mutations during meiosis. Due to random assortment, many gametes will not contain mutations. The fusion of two gametes with the same mutation will result in an offspring that is homozygous recessive for that mutation; it is likely that this offspring will not be viable. Asexual organisms do not have any means of purging mutations. Phylogenetic studies demonstrate that the long-term evolutionary persistence of asexual populations appears to be low. _______ Benefits of sexual reproduction Coping with environmental variation: offspring are likely to encounter different environmental conditions than their parents did. Offspring with genetic variation resulting from sexual reproduction have an increased probability of possessing gene combinations that will help them adapt to different conditions. Coping with parasites and pathogens: pathogens have much shorter generation times and larger population sizes than the host species they infect. This allows pathogens to evolve ways around host defenses, and forces hosts to rapidly evolve new defenses. _______ Benefits of sexual reproduction Red Queen Hypothesis: sexual selection allows hosts to evolve at a rate that counters the rapid evolution of parasites. Example: P. antipodarum snails in shallow waters can be infected with trematode worms. In shallow waters, more snails use sexual reproduction than snails in the deeper waters. Experiments demonstrated that trematodes were better at infecting shallow water snails than deep water snails. This demonstrates an evolutionary race between parasites and hosts. _________

Periodic cycles of populations

Cycles in laboratory populations Delayed density dependence may occur because the organism can store energy and nutrient reserves. Example: When populations are low and food is abundant, the water flea Daphnia galeata stores surplus energy as lipid droplets. When resources are less abundant, adults use this stored energy to reproduce. Eventually, lipid reserves are used up and the populations decline to low numbers. In contrast, Bosmina longirostris does not store energy and does not exhibit oscillations in population size. Cycles in laboratory populations Delayed density dependence can occur when there is a time delay in development from one life stage to another. Example: In a study of the sheep blowfly, A. J. Nicholson fed larvae a fixed amount of food but fed the adults unlimited food. The adult population increased to more than 4,000 individuals. As this occurred, larvae had less per capita food and eventually all larvae died. A few surviving larvae restarted the population. In a second experiment, he limited the food given to the adults. This limited reproductive output; eliminated the time delay, and caused the adult population to reach K and remain there. Cyclic population fluctuations Population cycles: regular oscillation of a population over a longer period of time. Some populations can exhibit highly regular fluctuations in size. Example: In the eighteenth century, gyrfalcons were captured and exported from Iceland for European nobility. Export records documented the number of falcons exported each year. Until 1770, gyrfalcons were intensely sought and records indicate a 10-year cycle in falcon abundance. Cyclic population fluctuations Cyclic populations can occur among related species and across large geographic areas (e.g., the synchronous cycles of the capercaillie, black, and hazel grouses in Finland). Foraging Behavior Cyclic behavior of populations Populations have an inherent periodicity and tend to fluctuate up and down, although the time required to complete a cycle differs among species. Populations behave like a swinging pendulum, which is stable when hanging straight up and down. Gravity will force the pendulum back to the center, but momentum causes it to overshoot the center. Populations are stable at their carrying capacity; when reductions in population sizes occur, the population responds by growing—often overshooting carrying capacity. Overshoots can occur when there is a delay between the initiation of breeding and the time that offspring are added to the population.

factors affecting population growth

Death .. Birth ... Immigration... Emigration

Factors that limit populations

Density-independent factor: natural disasters >>> density-dependent factor: the size of a population whose effect is dependent on the number of individuals in the population.

Population Distributions

Distributions of populations Spatial structure: the pattern of density and spacing of individuals in a population. Fundamental niche: the range of abiotic conditions (e.g., temperature, humidity, salinity) under which a species can persist. Competitors, predators, and pathogens may prevent a population from persisting in an area. Realized niche: the range of abiotic and biotic conditions under which a species can persist. Geographic range: a measure of the total area covered by a population (e.g., temperature and drought define the range of sugar maple). • ˗ • ˗ ˗ Distributions of populations Distribution reflects a hierarchy of limiting factors Climate and interactions with competitors Small-scale variation in the environment creates geographic ranges that are composed of small patches of suitable habitat. Example: The geographic range of Fremont's leather flower is just three counties in Missouri. Within those counties, plants are restricted to dry, rocky soils on limestone outcroppings (i.e., limestone glades). Plants are further restricted by variation in glade soil structure and quality. ____________ Distributions of populations We can test whether species are limited by unsuitable environmental conditions. Example: The Lewis' monkeyflower lives at high elevations, whereas the scarlet monkeyflower lives at low elevations. When planted outside their natural elevations, the two species grew poorly and experienced lower survival. This suggests that the plants are limited by unsuitable environmental conditions. Fitness is highest within normal range of species ___________

consequence of resources, predation, global warming, humans

Effects of global warming During the past century, the average temperature of the Earth has increased by 0.8°C. Temperature change can cause a shift in the geographic range of species. Example: Average temperatures in the North Sea have increased 2°C from 1977-2003. Fish species richness in the North Sea has increased steadily over this time, and is positively correlated with ocean temperature. Warmer northern temperatures have caused southern fish species to expand their ranges northward.

Fisher's reproductive value

Fisher's reproductive value The expected future number of offspring of a female of any age, given she has already made it to a certain age (a) ____ Populations Fisher's reproductive value What is the reproductive value of an adult semelparous organism? Va = ba Populations Fisher's reproductive value What is the reproductive value of an adult iteroparous organism? Va =b+b(alt/la)bt t=a+1 current future t=ama x Populations Other important parameters of a population can be estimated with these data Generation Time (T): "seed to seed" - average age at which females gives birth to their offspring - average time for a population to increase by a factor equal to net repro. rate (Ro) - average age of parents of all offspring produced by a single cohort Populations Other important parameters of a population can be estimated with these data Generation Time (T) = (xlxbx) / Ro Populations We have already calculated the average number of offspring produced by an individual (Ro) How do we calculate the per capita rate of increase (and what the heck is the difference!)? r = intrinsic rate of increase (as a rate, it can be positive or negative) r = lnRo / T ------- SEE NOTES FOR THE TWO CALCULATION EXAMPLES!!!!!!

Sex determination and ratio

Genetic sex determination In organisms with separate sexes, the sex ratio of male to female offspring is often one to one. Sex is often determined by inheritance of sex-specific chromosomes (e.g., human females have two X chromosomes (XX); males are XY). The sex that possesses two different chromosomes will produce an approximately equal number of gametes with each chromosome. On average, half of all offspring will be male; half will be female. In some, sex is determined by the presence or absence of a sex-specific chromosome. In bees, ants, and wasps, sex is determined by whether or not eggs are fertilized. _______ Environmental sex determination Environmental sex determination: a process in which sex is determined largely by the environment; this is a type of phenotypic plasticity, where the phenotype is sex. Temperature-dependent sex determination occurs when the sex of an individual is determined by the temperature at which eggs develop. Example: Many reptile species have temperature- dependent sex determination. For the Jacky dragon, females result if eggs are incubated at low or high temperatures; both sexes result at an intermediate temperature. This is adaptive (e.g., males produced at intermediate temperatures have more offspring than males from low or high temperatures). ____________ Offspring sex ratio Females can influence the sex ratios of their offspring. Examples: Females of some species can control whether X- or Y-chromosome sperm fertilize eggs. In hymenopteran insects, females can determine the sex of offspring by deciding whether or not to fertilize eggs. In red deer, male fawns are energetically expensive to care for; young (i.e., yearling) mothers often cannot find enough resources. Yearling mothers can selectively abort male embryos. This results in low male: female offspring; older (i.e., adult) mothers produce a nearly even ratio of male and female offspring because they are able to obtain enough resources. ___________ Frequency-dependent selection In most species, the sex ratio of males to females is nearly even. Frequency dependent selection: when the rarer phenotype in a population is favored by natural selection. In a population with an uneven sex ratio, the rarer sex will compete with fewer individuals for breeding; consequently, the rarer sex will experience higher fitness. Mothers that produce the rarer sex will experience increased fitness because her offspring will produce more offspring; selection should favor a mother that produces the rarer sex. As selection causes the rare sex to become common, the sex ratio of the population will eventually become even. ________ Sex Ratio • Frequency-dependent selection The rarer allele has the highest fitness For sex ratios among offspring, the rarer sex has more offspring on average than the more common sex. ____ Highly skewed sex ratios Skewed sex ratios may occur with local mate competition, which is when competition for mates occurs in a very limited area, and only a few males are required to fertilize all of the females. Example: Fig wasp mothers lay eggs inside of fig fruits and die shortly after. Mating among offspring occurs in the fig, and is often limited to brothers and sisters. Up to 90% of a fig wasp's progeny may be composed of daughters. Since females can lay a fixed number of eggs whereas males can fertilize many females, mothers should produce just enough males to fertilize all females.

survivorship curves

Graph of the proportion of a cohort-static still alive at each age.

Populations

Groups of individuals that belong to the same species and live in the same area

Human breeding system

Human breeding systems Work down by Murdock (1967) - Ethnographic Atlas sampled 849 traditional societies 708 / 849 (83%) were polygynous ~ half were <20% / half >20% 137 / 849 (16%) were monogamous 4 / 849 (0.004%) were polyandrous

Population Dynamics over Time

If diseases are highly infectious or have long periods of infectiousness, then high Ro

logistic equation VS EXPONENTIAL GROWTH MODELS!

LECTURE 14-15 In the logistic equation, each individual added to the population causes an incremental decrease in the per capita population growth rate. Exponential Growth Model 1/ N * d N/ dt Population size (N) Logistic Growth Model 1/ N * d N/ dt r m 0 negative population growth K Population size (N) 2 The logistic growth model As the population increases from a very small size, the rate of increase grows until reaching 1⁄2 the carrying capacity (corresponding to the inflection point). Rate of per capita increase can be modeled as: Individuals in the population continually decline in their ability to contribute to population growth. Density-dependence and factors that control Population Size Reproductive parameters are density-dependent

geometric growth

Let's take this example and calculate a rate of increase for the population. N0 = the number at time zero N1 = (2)N0, N2 = (2)N1, N3 = (2)N2 Now, lets substitute the value of N1 into the equation for N2 N2 = (2)(2)N0, in the same way N3 = (2)(2)(2)N0, and so on... To generalize: Nt=N0 (2)t The value 2 can be any number representing per capita rate. We will call it (lambda), Nt=N0t Nt=N0 t This is known as the geometric growth. It is called the geometric model because growth occurs in steps (i.e., reproduction occurs all at one time) _______

Mating systems

Mating systems Mating system: the number of mates each individual has and the permanence of the relationship with those mates. Sperm generally takes much less energy to produce than eggs. A female's reproductive success depends on how many eggs she can produce and mate quality; a male's success depends on the number of females he can fertilize. Promiscuity: males mate with multiple females and females mate with multiple males and do not create lasting social bonds; common among animals and outcrossing plants. ______ Mating systems Polygamy: a single individual of one sex forms long-term social bonds with more than one individual of the opposite sex. Polygyny: a polygamous mating system in which a male mates with more than one female. Polygyny may evolve when males compete for females, or when a male can defend territory and resources. Polyandry: a polygamous mating system in which a female mates with more than one male. Polyandry may evolve when females search for superior sperm or receive material benefits from each suitor (e.g., spermatophores). ______ Monogamy: when a social bond between a male and female persists through the period that is required for them to rear offspring. Favored when males make important contributions in raising offspring. Occurs in about 90% of bird species because males can offer similar care to offspring as females (e.g., incubating eggs, gathering food). Not common in mammals because males cannot provide the same care as females (e.g., lactation). ________ Extra-pair copulation: when an individual that has a social bond with a mate also breeds with other individuals. Females may use this strategy to obtain superior genotypes and produce offspring with better genetics. Example: Bluethroat chicks are commonly fathered through extra-pair copulation. These chicks have a better immune response (measured by wing swelling in response to an injection of foreign material). Mate guarding: a behavior in which one partner prevents the other partner from participating in extra-pair copulations. _____________________

microhabitat

Microhabitats Variation in habitat at a very fine scale is also important in determining local distribution valley vs. side of mountain and south vs. north facing slopes can vary 30o C air temperature can vary 10o C in only 2.6 m soil temperature is determined in part by soil color

Spatial models Population Structure and Growth

Models of spatial structure Subpopulations: when a large population is broken up into smaller groups that live in isolated patches. When individuals frequently disperse among subpopulations, the whole population functions as a single structure; all subpopulations increase and decrease in abundance synchronously. When dispersal is infrequent, each subpopulation fluctuates independently. *****Basic metapopulation model: a model that describes a scenario in which there are patches of suitable habitat embedded within a matrix of unsuitable habitat; all suitable patches are assumed to be of equal quality. 6 Models of spatial structure ****Source-sink metapopulation model: a population model that builds upon the basic metapopulation model and accounts for the fact that not all patches of suitable habitat are of equal quality. Source subpopulation: in high-quality habitats, subpopulations that serve as a source of dispersers within a metapopulation. Sink subpopulation: in low-quality habitats, subpopulations that rely on outside dispersers to maintain the subpopulation within a metapopulation. 6 Models of spatial structure *****Landscape metapopulation model: a population model that considers both differences in the quality of the suitable patches and the quality of the surrounding matrix (e.g., habitat corridors). Represents the most realistic and most complex spatial structure of populations. ______________ Population demography Demography: the study of populations. In the 19th century, Charles Darwin and other scientists realized that the study of demography could apply to all organisms on Earth. Growth rate: in a population, the number of new individuals that are produced per unit of time minus the number of individuals that die. Intrinsic growth rate (r): the highest possible per capita growth rate for a population. Under ideal conditions, individuals experience maximum r (i.e., maximum reproductive rates and minimum death rates).

Dispersal

Population dispersion Dispersion: the spacing of individuals with respect to one another within the geographic range of a population. Clustered dispersion: when individuals are aggregated in discrete groups (e.g., social groups or clustering around resources). Evenly spaced dispersion: when each individual maintains a uniform distance between itself and its neighbors (e.g., defended territories, croplands). Random dispersion: when the position of each individual is independent of other individuals; not common due to non-random environmental heterogeneity. _________________ Population dispersal Dispersal: the movement of individuals from one area to another. Dispersal is distinct from migration, which is the seasonal movement of individuals back and forth between habitats. It is the mechanism by which individuals can move between suitable habitats. Dispersal allows species to colonize areas outside of their geographic ranges. Dispersal can be a way to avoid areas of high competition or high predation risk. ________________

Distribution characteristics

Population distributions have five important characteristics Geographic range: all the areas where a species is found. Abundance: total number of individuals. Density: number of individuals per unit area or volume. Dispersion: spacing of individuals. Dispersal: the movement of individuals from one area to another ______________ Population characteristics Endemic: species that live in a single, often isolated, location. Cosmopolitan: species with very large geographic ranges that can span several continents. Abundance: the total number of individuals in a population that exist within a defined area (e.g., total number of lizards on a mountain). The total abundance of a population provides a measure of whether a population is thriving or on the brink of extinction. ______________ Population density Density: in a population, the number of individuals per unit area or volume; calculated by dividing abundance by area. If population density is greater than what the habitat can support, some individuals must leave or the population will experience lower growth and survival. The largest density of individuals typically occurs near the center of a population's geographic range. Near the edges of the range conditions become less ideal, and population densities decrease. _____________

Discrete population growth

Reproduction is seasonal, growth rate is represented by lambda

Red Queen Hypothesis, snails and flatworms, why two sexes, isogamy and anisogamy,

Sex, snails and pathogens Predictions: 1. Pathogen should have greatest success infecting snails from same population (they co-evolved together) Sex, snails and pathogens Predictions: 2. If parasites evolve higher rates of infection on common clones, rare snail clones should increase and common ones decrease over time (creating cycles) _________

challenges to the traditional view of breeding systems intersexual conflict

Sexual conflict Mating partners often behave according to their own self-interest. Examples: When a dominant lion takes over a pride, he often kills newborn cubs fathered by a previous dominant male. Females without newborn cubs are able to breed more quickly, so this allows the new dominant male to breed sooner. Male bedbugs mate by stabbing females with a sperm-transferring appendage. Fertilized females live shorter lives and lay fewer eggs. This may have evolved because females tend to resist copulation attempts. Conflict over Mating • Reproductive interests of males and females will often be different - The result is a conflict of interest between two sexes • • - • - • Sexual Conflict Physiological mechanisms A conflict of interests between sexes can result in co- evolutionary sequence similar to that between host and parasite Male fruit fly seminal fluid contains molecules that influence female egg laying rate and remating frequency Beneficial to the male because these adaptations will increase the number of eggs fertilized by his sperm Fluid is toxic to females and shortens her lifespan Favors resistance in females Process leads to co-evolutionary "counter moves" by each sex Conflict over Mating • Divergent interests may lead to conflict over paternity - Results in co-evolution between sexes Conflict over Mating • Process leads to co-evolutionary "counter moves" by each sex

sexual size dimorphism

Sexual dimorphism Many differences between sexes in size, appearance, physiology, & behavior • - - Divergent life histories as related to reproduction may lead to dimorphism females of some species (e.g., spiders) are larger than males because the number of offspring produced varies with size May be especialy common in species with internal fertilization and low levels of sperm competition Sexual dimorphism Sexual dimorphism • For other systems, sex itself provides solution to puzzle of sexual dimorphism

Sexual vs. asexual reproduction

Sexual reproduction Sexual reproduction: a reproduction mechanism in which progeny inherit DNA from two parents. Gonads: the primary sexual organs in animals. Sexual gametes are produced through meiosis, which results in haploid cells containing a single full set of chromosomes. Haploid gametes fuse together to produce a diploid zygote. The distribution of parent chromosomes into the haploid cells is generally random. Mixing of the chromosomes from the two parents results in new combinations of genes in the offspring. ________ Asexual reproduction Asexual reproduction: a reproduction mechanism in which progeny inherit DNA from a single parent. Vegetative reproduction: a form of asexual reproduction in which an individual is produced from the nonsexual tissues of a parent. Many plants reproduce vegetatively from leaf, root, or rhizome tissue (e.g., walking ferns). Clones: individuals that descend asexually from the same parent and bear the same genotype. Binary fission: reproduction through duplication of genes followed by division of the cell into two identical cells. Parthenogenesis: a form of asexual reproduction in which an embryo is produced without fertilization. Animals that reproduce by parthenogenesis are typically all female. Relatively rare in vertebrates. A few examples exist, such as the female boa constrictor that gave birth to two litters of daughters through parthenogenesis. Clones result when germ cells develop directly to egg cells. Genetically variable offspring result when germ cells undergo partial or complete meiosis. ______ Comparing sexual strategies Natural selection should favor the strategy with the highest fitness. If a male can invest in female function while giving up only a small amount of male fitness (or vice versa), selection should favor hermaphroditism. Example: In the case of flowers, the flower structure and floral display are present whether an individual is male or female. The cost of adding a sexual function should be relatively small while providing large fitness benefits. __ Comparing sexual strategies In some cases, the fitness cost of investing in a second sexual function is too high to offset the fitness benefits of hermaphroditism. Example: For many animals, adding a second sexual function requires the growth of complex organs for transmitting gametes. Becoming a male often requires large amounts of time and energy to attract mates and fight with other males. Becoming a female often requires large amounts of time and energy to produce and care for offspring. Among animals, hermaphroditism should occur only among sedentary aquatic animals that simply shed gametes in the water.

breeding system and sexual selection

Sexual selection Females have a limited number of eggs and should select males that maximize her fitness. Males should compete with other males for breeding opportunities. Sexual selection: Natural selection for sex-specific traits that are related to reproduction; leads to a variety of differences between males and females. Sexual dimorphism: the difference in the phenotype between males and females of the same species (e.g., body size, courtship behavior). Primary sexual characteristics: traits related to fertilization. Secondary sexual characteristics: traits related to differences between the sexes in terms of body size, ornaments, color, and courtship. -_____ Sexual Selection Natural Selection - differential reproductive success of individuals in a population based on genetic differences among them. Sexual Selection - selection on variation among one sex (the "limited" sex) in obtaining fertilizations (differential fertilization success) Sexual Selection • - - Two mechanisms of sexual selection: Intrasexual competition: competition among the limited sex for access to the limiting sex morphological traits that favor victory in "combat" alternative strategies to obtain matings Round goby males Sexual Selection Classic Study in sexual selection - elephant seals Sexual Selection Female Natural History • can breed at two years, successful after four • 10-12 feet long, weigh 900 kg • live for ~14 years • pregnant females give birth within 5-6 days after returning to annual breeding site • stay in groups while on shore (up to 400) • fast for 3-4 weeks while nursing • last 3-5 days of nursing, go into estrous • copulate and then wean pup by returning to sea • season lasts for ~1 month Sexual Selection Male Natural History • mature at 5 - 6 years • 16 feet long, 2.5 - 4.5 tonnes (can be as much as ten times larger than females) • males fight for access to females • fights may last up to 45 minutes • fights lead to linear dominance hierarchy • top male (the "alpha" male) controls central area • will move if females move • in any given year, 1/3 of males achieve copulations • top five get 90% of copulations • breeding season lasts 3 months Sexual Selection Male Strategies • wait in water for females to leave • challenge male after long fight • try different harems • imitate females to gain access Sexual Selection Sexual Selection Study Results 68 69 70 71 72 73 74 RAT STP GLS ADR - 0 0 1 48 18 x 0 2 50 1 x x x 16 90 6 x x x x - 0 3 81 37 50 x Most males = 0 Females = 1 per year Sexual Selection Two mechanisms of sexual selection: Mate choice (intersexual competition): the limiting sex (usually female) chooses among the "limited" sex with whom to mate offering of nutrients, territories, or other necessary resources elaborate male plumage and/or courtship displays may result _____

sexual strategies, sex roles, sex ratios,

Sexual strategies Most vertebrates and some plants have separate sexes; most plants and some vertebrates are hermaphrodites. Perfect flowers: flowers that contain both male and female flowers. Simultaneous hermaphrodites: individuals that possess male and female reproductive functions at the same time. Sequential hermaphrodites: individuals that possess male or female reproductive function and then switch to the other. Monoecious: plants that have separate male and female flowers on the same individual. Dioecious: plants that contain either only male flowers or only female flowers on a single individual.

Reproductive Strategies

Sexual strategies Most vertebrates and some plants have separate sexes; most plants and some vertebrates are hermaphrodites. Perfect flowers: flowers that contain both male and female flowers. Simultaneous hermaphrodites: individuals that possess male and female reproductive functions at the same time. Sequential hermaphrodites: individuals that possess male or female reproductive function and then switch to the other. Monoecious: plants that have separate male and female flowers on the same individual. Dioecious: plants that contain either only male flowers or only female flowers on a single individual. _______ Selfing vs. outcrossing For hermaphrodites, self-fertilization (i.e., selfing) occurs when an individual's male gametes fertilize its own female gametes. Since this poses a cost due to inbreeding depression, selection should favor individuals that can breed with other individuals (i.e., outcrossing) when possible. Sequential hermaphroditism avoids the problem of selfing by separating sexual functions in time. Some species have self-incompatibility genes that prevent an organism from being able to self. _____ Mixed mating strategies Some species are able to switch between outcrossing and selfing. When mates are available, individuals outcross. When mates are unavailable, individuals self-fertilize; this may not produce as many viable offspring, but it is better than nothing. Mixed mating can be in response to a lack of resources in the environment. Example: When herbivores consume leaves, plants must expend energy for new tissue growth. In response, some plants such as the orange jewelweed increase rates of self-fertilization.

Social Behavior

Social behaviors Social behaviors: interactions with members of one's own species, including mates, offspring, other relatives, and unrelated individuals. Social behaviors have a genetic basis and are subject to natural selection. Selection has favored cohesive groups and constrained antagonism. Many organisms other than animals exhibit social behaviors. Examples: Bacteria and protists can secrete chemicals to sense each other, and react in "friendly" or "aggressive" ways. Damaged plants emit volatile chemicals that warn other plants. ___ Group benefits A group may be able to fend off predators better than an individual. Dilution effect: the reduced, or diluted, probability of predation to a single animal when it is in a group. More individuals watching for predators allows each individual to spend less time watching, and more time feeding. Example: As flock size of European goldfinches increases, the total amount of time the group spends watching for predators increases. The individual amount of time an individual spends watching decreases. Group benefits Many individuals searching for food may be able to find rare food more easily. Probability of prey capture may increase in a group. Being social makes it easier to find potential mates because large groups attract the attention of females. Lek: the location of an animal aggregation to put on a display to attract the opposite sex. Example: Larger leks of ruffs (a wading bird) attract more females, resulting in an increased percentage of successful male copulations. Group costs Groups of animals are more conspicuous to predators. The risk of parasites increases in groups; high densities can increase the rate at which diseases spread. Risk of disease spread is particularly problematic in aquaculture or livestock operations, where animals are kept at high densities. Example: Tropical fish that live in higher densities on reefs that are not fished (i.e., protected) also have more parasites. Group costs Larger groups are better able to locate food, but that food must be shared among all members. Example: Large flocks of the European goldfinch consume seeds in an area much faster than small flocks. Large flocks have to spend more time flying between patches of seeds. Each bird has to spend more time and energy looking for food. Group costs Living in groups can lead to aggression among members. Example: Chickens are well-known for fighting when raised under crowded conditions. When one chicken receives an injury that causes a spot of blood on its feathers, other chickens will peck at the spot, causing more injury, more spots of blood on other chickens, and more group fighting. Allowing only best-performing social groups (i.e., those that exhibit less fighting) selects for chickens that behave better in groups and that have a greater lifetime egg production. ---- Territories Territory: any area defended by one or more individuals against the intrusion of others. Defending a high-quality territory generally assures greater resources (e.g., food, nest sites). Territories can be transient or relatively permanent. Examples: Many migratory bird species will establish summer breeding territories for months. Shorebirds that stop along their migration route may defend areas for a few hours or days before continuing on their journey. Dominance hierarchies Dominance hierarchy: a social ranking among individuals in a group, typically determined through contests such as fighting or other contests of strength or skill. Occurs when defending a territory is impractical; such as when conspecific density is high and it is not possible to defend against all of them. Once a hierarchy is established, contests are resolved quickly in favor of the first-ranked member. First-ranked members dominate all; second-ranked members dominate all but first-ranked, and so on.

temporal variation and age structure

Temporal variation refers to change with time, while spacial variation means change in places or in geographical locations Age structure fluctuations When an age group contains a high or low number of individuals, the population likely experienced high birth or death rates in the past. Example: From 1946-1951, researchers determined the age of harvested whitefish by examining their scales. In 1947, there was a large number of 3-year- old fish. This cohort continued to dominate the population's age structure in subsequent years. Age structure fluctuations Long-term fluctuations in age structure can be determined for a forest by examining tree rings. Example: In a Pennsylvanian forest, researchers removed samples of wood from tree trunks to count growth rings. In the 1500s, the forest was largely composed of several species of oak trees. Fire and drought in the mid-1600s led to an increase in white pine trees. As the white pines grew, they shaded out conspecifics and allowed American beech and eastern hemlock trees to grow.

Sexual conflict

The evolution of phenotypic characteristics that confer a fitness benefit to one sex but a fitness cost to the other.

The logistic growth model

The logistic growth model Carrying capacity (K): the maximum population size that can be supported by the environment. Logistic growth model: a growth model that describes slowing growth of populations at high densities; it is represented by: S-shaped curve: the shape of the curve when a population is graphed over time using the logistic growth model. Inflection point: the point on a sigmoidal growth curve at which the population has its highest growth rate. 2 The logistic growth model Example: Georgyi Gause raised two species of protists in test tubes and added a fixed amount of food each day. Populations initially grew in size, but eventually stabilized at different carrying capacities. To test whether carrying capacities were determined by the amount of resources, he doubled the amount of food in each test tube. With twice as much food available, populations grew to sizes that were twice as large as those in the first experiment.

time lags (effect of r and τ)

Time lag - when the response to density is time delayed. Individuals do not immediately adjust reproduction when resources change and these delays can affect population dynamics. 1. Seasonal availability of resources 2. Growth responses of predator populations How to incorporate time lags into the model? dN/dt = rN(1-N/K) dN/dt is controlled by population size at some time t - (tau) in the past dN/dt = rN(t)(1-Nt- /K) The behavior of this equation depends on two factors: 1. Length of the time lag 2. "Response time" of population (populations with fast growth have short response time) 3. These two factors expressed as the product "r" The size of the product controls population growth. 1. Small r - pop. increases smoothly to K 2. Medium r - damped oscillations 3. Large r - stable oscillations with amplitude increasing with r

Doubling time

Time period required for a population experiencing exponential growth to double in size completely.

Ideal free distribution

When individuals distribute themselves among different habitats in a way that allows them to have the same per capita benefit - assumes perfect knowledge of habitat variation

Why two sexes

Why two sexes? Primitive Condition = Isogamy (all gametes are the same size) ... ch.11

growth rates

___________ is the amount of increase that a specific variable has gained within a specific period and context.

Estimating distribution properties Geographic range and body size

_________________________ Population fluctuations All populations experience fluctuations due to factors such as availability of resources, predation, competition, disease, parasites, and climate. Fluctuations include random and cyclic changes through time. Some populations tend to remain relatively stable over long periods. Example: Over 30 years, the population of red deer on the Isle of Rum in Scotland has remained relatively stable. Population fluctuations In contrast, some populations exhibit much wider fluctuations. Example: Over a single year, the algae population in Lake Erie exhibits wide fluctuations from 0-7,000 cells per cm3. Small organisms (e.g., algae) tend to reproduce much faster than larger organisms (e.g., red deer), so their populations often respond faster to favorable and unfavorable conditions. Larger organisms have a lower surface-area-to-volume ratio, which allows them to maintain homeostasis in the face of unfavorable environmental changes. Age structure fluctuations When an age group contains a high or low number of individuals, the population likely experienced high birth or death rates in the past. Example: From 1946-1951, researchers determined the age of harvested whitefish by examining their scales. In 1947, there was a large number of 3-year- old fish. This cohort continued to dominate the population's age structure in subsequent years. Age structure fluctuations Long-term fluctuations in age structure can be determined for a forest by examining tree rings. Example: In a Pennsylvanian forest, researchers removed samples of wood from tree trunks to count growth rings. In the 1500s, the forest was largely composed of several species of oak trees. Fire and drought in the mid-1600s led to an increase in white pine trees. As the white pines grew, they shaded out conspecifics and allowed American beech and eastern hemlock trees to grow. Overshoots and die-offs Populations in nature rarely follow a smooth approach to their carrying capacity. Overshoot: when a population grows beyond its carrying capacity; often occurs when the carrying capacity of a habitat decreases from one year to next (e.g., because less resources are produced). Die-off: a substantial decline in density that typically goes well below the carrying capacity. Die-offs often occur when a population overshoots its carrying capacity. Cyclic population fluctuations Population cycles: regular oscillation of a population over a longer period of time. Some populations can exhibit highly regular fluctuations in size. Example: In the eighteenth century, gyrfalcons were captured and exported from Iceland for European nobility. Export records documented the number of falcons exported each year. Until 1770, gyrfalcons were intensely sought and records indicate a 10-year cycle in falcon abundance. Cyclic population fluctuations Cyclic populations can occur among related species and across large geographic areas (e.g., the synchronous cycles of the capercaillie, black, and hazel grouses in Finland). Foraging Behavior Life History Evolution

landscape models

a model that considers both the differences in quality of suitable patches and quality of surrounding matrix.

Four processes affect population growth

birth, B = number born into a population per unit time death, D = number dying in a population per unit time immigration, I = number moving into a population per unit time emigration, E = number moving out of a population per unit time _____ If interested in knowing the number of individuals from time t to time t + 1... Nt + 1 = Nt + B - D + I - E N = B+I-D-E (change in population size) In practice we like to assume that the population is closed (i.e. I and E are zero), so we only have to worry about B and D. (N = B - D) Living populations do not change by constant numbers, but rather each individual has the potential to reproduce. We assume the population is growing smoothly. 300 spiders per year 150 spiders per six months 1.64 spiders per 2 days... Continuous growth is an approximation. But it allows us to describe growth as a continuous differential equation dN / dt = B - D What exactly do B and D represent in this equation? B and D represent number of births/deaths over very short period of time (because of differential equation) They are still dependent on population size (1000 birds lay more eggs than 25, even in a short time period) So, B = bN where b is the instantaneous birth rate (births / individual time) and D = dN where d is the instantaneous death rate (deaths / individual time) Substituting and simplifying: dN / dt = (b - d)N Per capita growth rate then is b - d = r (r = intrinsic rate of increase) For populations that reproduce continuously, the equation that describes their growth is: dN/dt=rN The solution to this equation is: Nt=No ert Because the population has a rate of reproduction (each individual in the population has the potential to reproduce), the type of growth of the population will be... Exponential growth! How does r affect population growth? r>0 r=0 r<0 N Time Assumptions of the Continuous Population Growth Model 1. Constant b and d (no density dependence) 2. No genetic structure 3. No age or size structure 4. Continuous growth that is a function of current size (no time lags) Population Structure and Growth Populations Life tables Continuous population growth Doubling time One way to compare population growth is to use the idea of doubling time. Doubling time is the amount of time required for a population to double given a constant r-value.

Handicap principle

explains how evolution may lead to "honest" or reliable signaling between animals which have an obvious motivation to bluff or deceive each other.

Life History Evolution

explains the design of phenotypes for reproductive success

What is a population? Ecological niche

group of organisms of the same species living in a particular geographic area -- Ecological niche modeling As a general rule, populations can grow larger in more suitable habitats. Understanding the realized niche of a species aids in species conservation and can help to limit the spread of invasive species. Ecological niche modeling: the process of determining the suitable habitat conditions for a species. Ecological envelope: the range of ecological conditions that are predicted to be suitable for a species (differs from the realized niche, which describes conditions in which a species currently exists). Predicting the potential geographic range of a species is difficult when only a few individuals exist; researchers can use historic distributions of species. ------ Modeling invasive species Ecological niche modeling can predict the expansion of pest species. Example: The Chinese bushclover was brought to the United States to control erosion, provide cattle feed, and reclaim mined land. Ecologists collected data on the environmental conditions under which bushclover lived in eastern Asia. They used this data to quantify the ecological envelope of bushclover and predicted all locations to which it subsequently spread. Since bushclover has not spread to all predicted locations, other ecological factors may limit its distribution.

Separate sexes vs. hermaphrodites

hermaphrodites: a person or animal having both male and female sex organs or other sexual characteristics, either abnormally or (in the case of some organisms) as the natural condition.

Ideal free distribution

lecture 14-15 The ideal free distribution Whenever possible, individuals choose habitats that provide the most energy. As individuals move to a high-quality habitat, resources must be divided among more individuals (i.e., reduced per capita benefit). Per capita benefit can fall so low that an individual would benefit by moving to the low-quality habitat. Ideal free distribution: when individuals distribute themselves among different habitats in a way that allows them to have the same per capita benefit; assumes perfect knowledge of habitat variation. Ideal Free Distribution • Ideal - because individuals choose a habitat (a "patch") based on where rewards are highest • Free - because are able to disperse where they wish • A word about mathematical models... Ideal Free Distribution - Assumptions • Move among patches with no or minimal cost • Knowledge of all patches • Knowledge of what others are doing • Patch use (food intake) is related to fitness • All individuals are of equal quality • As number of foragers increase, suitability of patch decreases ______ Ideal Free Distribution - Predictions • Proposed as a "null" model • Feeding rate will be same, regardless of patch quality • Distribution of individuals will be proportional to distribution of resources /--_______________-- The ideal free distribution Stickleback fish were distributed evenly throughout an aquarium. Researchers manipulated the abundance of prey (i.e., water fleas) on each side of the aquarium such that one side had one-fifth the abundance of water fleas as the other side. Within five minutes of starting the experiment, the fish distributed themselves across the aquarium in a ratio that was approximately four to one. When the abundance of food on each side was changed, the fish quickly adjusted their distribution ratio. ___________ The ideal free distribution Individuals in nature rarely meet the expectations required by the ideal free distribution. Individuals may not be aware that other habitats exist. Fitness is not solely determined by maximizing resources; other factors may influence distribution such as the presence of predators or territory owners. 6 The ideal free distribution The ideal free distribution can allow populations in low-quality habitats to persist over time. Example: Blue tits breed in both downy oak and holm oak forests. Downy oak forests produce six times as many caterpillar prey. Downy oak forests support more breeding pairs, and pairs produce more offspring. Holm oak bird populations would experience an annual decline of 13% if they were not supported by dispersal of offspring from downy oak forests.

Summary of exponential models

most popular

heterogeneity of habitat

promoting beta diversity and ultimately contributing to overall higher global diversity.

Continuous population growth

reproduce at variable times, not seasonally; exponential population growth will occur; dN/dt=rN

Hamilton-Zuk hypothesis

specifically proposes that females choose males with features that are honest indicators of low parasite load (parasite resistance)

Senescence

the natural physical decline brought about by aging

runaway selection

trait becomes reinforced generation after generation until it is greatly exaggerated ( until there is no variety can be produced.