Ecology Exam 2 Flashcards
monogamy
pair bond between female and male
polygamy
several of one sex, only one of the other
polygyny
one male, several females
polyandry
one female, several males
simultaneous
multiple pair bonds occur at same time
simultaneous polygyny
one male with two or more females at the same time
simultaneous polyandry
one female with two or males at the same time
sequential
multiple pair bonds occur over a single breeding season
sequential polygyny
one male with two or more females, but only one at a time
sequential polyandry
one female with two or more males, but only one at a time
difference between males and females
females have larger gametes and care for the developing zygote, males have smaller gametes and play less of a role
what does greater female investment mean
this sex generally has fewer offspring and thus pays more attention to offspring quality
as sexual dimorphism increases…
males more able to ‘defend’ multiple females and probability of polygyny increases
polygyny threshold
territory quality varies so much that it is better for a female to mate with an already-mated male on ‘good’ territory than to mate with a monogamous male on ‘bad’ territory
monogamy may be favored when…
offspring require attention from both parents
95% of passerine birds are monogamous, when are they polygynous?
polygyny occurs in productive and patchy environments (areas with good and bad places for feeding young)
monogamy isn’t perfect because of…
extra-pair paternity
extra-pair paternity
father raising some offspring belonging to another males
why is polygyny in lizards extremely common?
lizards have no parental care
why are mammals more likely to be monogamous?
females have a larger investment in offspring than males and are predisposed towards more parental care than males
what is a greater male to female ratio correlated with?
higher likelihood of polygyny
when polygyny occurs in yellow bellied marmots, what is the result?
females tend to suffer and prefer monogamy, males benefit and prefer polygyny (harems); males must work hard to maintain harems
why do tinamou engage in sequential polyandry?
the males give parental care rather than females
what makes polyandry more likely?
kin selection
what are two alternative sexual strategies?
- if you’re not winning, change the game
- sex change
what are examples alternate strategies?
cuttlefish males pretend to be females until they’re large enough to compete with other males
lekking male tries to attract females, satellite males sneaks copulations at edge of lek
sunfish males are territorial or non-territorial, non-territorial sneak in and fertilize eggs
dung beetles are horned (large and mate) or hornless (smaller, alternate burrow to sneak in and mate)
what are examples of sex change?
if the male in hogfish population disappears, most dominant female becomes the male
younger crepidula mollusks settle on older mollusks, youngest are males and oldest are females, males become females as they age
types of geographic range
extensive and restricted
types of habitat tolerance
broad and narrow
types of local population size
large and small
how are sessile organisms dispersed in space?
random, clumped, or uniform (overdispersed)
what can happen in uniform dispersion?
organisms may be poisoning one another or using up nearby resources
what can happen in clumped dispersion?
habitat clumped or mutualisms may be occurring between organisms
how can a single individual be used to characterize space use in mobile organisms?
use radio transmitter or other tracking device, get set of points and use them to calculate home range
home range
area that is ‘normally’ frequented by the animal
minimum convex polygon method
smallest area that encloses all points or has points on boundaries, no inner angle > 180 degrees
behavioral definition of territory
a defended area
ecological definition of territory
an exclusive area (no other animal or group occurs there)
center of gravity method
take home range and compute average X and Y coordinates in space; if home ranges are on average spaced out, they are over-dispersed and probably territorial
what broadly determines territory size?
balance between benefits and costs
what happens to benefits as territory size increases?
benefits first increase, then level out because you ‘max out’ the resources you utilize
what happens to cost as territory size increases?
costs accelerate with larger territory diameters because area = (pi)r^2
what is the optimal solution to territory size?
max benefits while minimizing costs
what happens to territory size if territories improve (more resources, less risk of predation)?
territory size should decrease
what happens to territory size as competitors become more numerous?
territory size decreases
what specifically determines territory size?
avoidance of predation
increase or facilitate mating opportunities
competition for other limiting resources
increased food supply
effect of avoidance of predation
animals defend territories because those with territories are less vulnerable to predators
familiarity with good hiding places
spacing
effect of increase or facilitate mating opportunities
reproduce undisturbed
increased number of potential mates with larger territory
effect of competition for other limiting resources
compete for reproductive sites, etc.
increased food supply effects who in a territory?
an individual or pair defending territory
offspring raised on territory
future offspring
as organism’s food requirement (metabolic rate) increases…
territory size should increase
as food density increases…
territory size should decrease
interspecific (between-species) evidence for increased food supply motivating territoriality
larger organisms have larger territories
predators have larger territories than herbivores of same weight
intraspecific (within-species) evidence for increased food supply motivating territoriality
snowy owl and lemmings (Pitelka): Territory size of snowy owls inversely correlated with lemming density.
nuthatches (Enokkson and Nilsson): Both observational and experimental work show that territory size decreases as food density increases
fence lizards, Sceloporus sp. (Simon): Both ♂ and ♀ defend territories (males are larger and have larger territories). For both ♂ and ♀, territory size inversely
correlated with food density. When food density increased by adding mealworms, territory size decreased. When food addition stopped, territory size increased
other adaptive rationales for territoriality
australian magpie (Carrick): defend territories in small groups from other flocks. Surveys found that group size is unrelated to territory size; disease avoidance
may drive territory defense.
dragonfly territories: may function as mating sites or prevent other dragonflies from laying eggs on its territory (decreasing food competition for its offspring).
sex ratio
number of males per female
primary sex ratio
sex ratio of all individuals at birth; may change over time because of differential survival
sex ratio in polygynous species
male mortality is greater than female mortality, so as population ages the sex ratio decreases
secondary sex ratio
sex ratio at reproductive maturity
why do sex ratios tend towards 50:50?
R.A. Fischer’s argument for maintenance
1. in diploid species, every organism has a male and female parent that contribute equally to future generations
2. if mutation changes sex ratio, the rarer sex becomes more valuable that the more common sex
3. since rarer sex is more valuable, selection favors rarer sex –> back to 50:50
what are complications with R.A. Fisher’s argument?
- if one sex is more costly to produce per individual, fewer of that sex will be produced –> total cost of male production should equal total cost of female production
- if males and females experience different mortality rates between birth and maturity, primary sex ratio should shift in order to produce 50:50 secondary sex ratio at maturity
sex ratio in atlantic silversides
low water temp –> females produced
high water temp –> males produced
if silversides are kept in only warm water, strong selective pressure for individuals capable of producing females to restore 50:50 ratio
sex ratio in polygynous anolis lizards
large offspring have higher fitness as males, small offspring have higher fitness as females
mothers in good condition should produce males, mothers in poor condition should produce females
when might larger females be advantageous?
larger mothers may be able to carry more eggs, raise better offspring
parasitic wasp example
hole size determines weevil larvae size –> corn kernels with larger holes produce more females, smaller holes produce more males
age structure
% of individuals in different age classes
type I survivorship curve
low initial mortality, with most mortality occurring at older ages (not common: humans, some large mammals and lizards)
type II survivorship curve
equal chance of dying at all ages (uncommon: most birds, lizards, some mammals)
type III survivorship curve
high initial mortality, lower mortality in older organisms (most common: most invertebrates, plants, many fishes, etc.)
cohort
those individuals in the population born during a specific time interval (example: 1/1/1987 through 12/31/1987)
Lx
% of individuals in a cohort surviving to age X (probability from surviving from birth to age X)
Mx
‘fecundity’ –> the number of offspring produced by an individual of age X while at that age (NOT a probability)
R0
net reproductive rate –> the average number of offspring per female over the course of its lifetime, averaged across all ages
equation for R0
R0 = Σlxmx
If R0 > 1…
the population is growing
If R0 < 1…
the population is decreasing
generation time
average age of reproduction
generation time simple calculation
generation time = (α + ω)/2
generation time complex calculation
generation time = Σxlxmx /R0
why add complexity to the equation?
organisms may differ in likelihood of reaching different ages, or in number of offspring produced at each age
Va
reproductive value –> the number of offspring expected to be produced by an organism of age A over the rest of her life
why does Va initially increase over time?
newborn organisms may die before reproducing, an organism just entering reproductive maturity is more valuable than an infant
organisms with which survivorship curve should focus on conservation and resource management?
type III
λ
geometric rate of increase –> the ratio of population size at two points in time
when does R0 not equal λ?
if a species has overlapping generations and/or continuous reproduction
T
average generation time per population
T equation
T = (ΣXLxMx)/R0
r
intrinsic rate of increase for a population (r = per capita births - per capita deaths)
r equation
r = ln(R0)/T
Nt
number of individuals at time t
N0
number of individuals at t = 0
geometric population growth equation
Nt = N0λ^t
when is geometric population growth used?
for organisms that experience pulsed reproduction (example: insects that produce a single generation per year, annual plants, etc.) –> generations CANNOT overlap
when is exponential population growth used?
for organisms with continuous population growth in an unlimited environment
exponential population growth equation
Nt = N0e^(rt)
exponential growth equation expressed as a differential equation
dN/dt = rN
or
dN/dt = B - D = (b - d)N = rN; where N = total number of individuals in population, B = raw number of births, D = raw number of deaths, b and d = per capita rates of birth and death
effect of r on population growth rate (exponentially)
large r = faster rate, small r = slower rate
K
carrying capacity of species (limit to population size of that species in that area)
when is K higher?
on larger islands or in better habitats
logistic population growth equation
dN/dt = rN[1 - (N/K)]
If N is small…
N/K ≈ 0 and ‘drops out’
dN/dt = rN (1-0) = rN(1) = rN = exponential growth
If N is large…
N/K ≈ 1
dN/dt = rN(1-1) = rN(0) = no growth
r is highest when…
N is lowest and declines as a linear function of N
reaches zero when N=K
what is the max value of dN/dt?
at K/2
optimal yield
N at which dN/dt is highest
population size that should be maintained for max harvest rate
effect of varying r vs. K
the larger the r, the quicker the ‘slope’/more steep the slope
the larger the K, the higher the max N
when is the logistic growth equation appropriate?
best fit with small, rapidly reproducing organisms with uniform populations (individuals are very similar to one another)
in larger organisms, population age structure creates oscillations as individual large organisms are more variable
logistic growth equation with time lag
dN/dt = rN_t[1 - (N_(t-L)/K)]
L
time lag
effect of L
the larger L is, the more oscillations in the graph
why add time lag?
present population size (N_t) and K are not as relevant as past population size (N_t-L) and K
development takes time, reproductive output is not yet in sync with present conditions and time lag is necessary
per capita growth rate equation
PCGR = (dN/dt)/N
PCGR decreases as N increases
negatively density-dependent
PCGR increases as N increases
positively density-dependent
PCGR is unrelated to N
density-independent
how might negative density-dependence happen?
competition for resources
competition for territories
increased crowding increases disease prevalence
how might positive-density dependence happen?
more mating opportunities if more individuals around
large groups defend against predators and get resources more efficiently
how might density-independence happen?
weather, catastrophes, natural disasters
