Lecture #3 Review. Reproduction, Migration and Dispersal 1) Sex is nearly universal, despite its considerable costs to organisms. Its value is the maintenance of genetic diversity, which increases adaptability to environmental challenges.
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Reproduction, Migration and Dispersal
1) Sex is nearly universal, despite its considerable costs to organisms. Its value is the maintenance of genetic diversity, which increases adaptability to environmental challenges.
2) Sexes may be separate (in gonochoristic species), simultaneous, or sequential in the same body. The contributions of different sexes to the next generation determine the value of hermaphroditism, as well as the relative sizes of males and females. For example, if the relative advantage of a sequential hermaphrodite functioning as a large female and small male have an advantage in maximizing offspring production, this will select for male-female transitions..
3) Fertilization success is affected by the mode of sperm transfer, the volume of gamete production, the distance between males and females, water turbulence, the timing of spawning, and behavior. Free spawning has a number of costs, and planktonic gametes have special problems in ensuring fertilization, but specialized sperm attractants exist.
4) Marine species differ in parentalcare. Most species have free-swimming larvae, but some guard or brood eggs, brood young within body cavities, or have live birth like mammals.
5) Inalgae and corals, nonsexual reproduction involves colonial individuals (modules) that are connected to each other and exchange nutrients.
6) Gamete production and larval life must be timed to allow settlement and promote dispersal, to avoid being swept to inappropriate habitats, and to counter predation. Egg size decreases with increasing egg numbers.
7) Marine invertebrate offspring may be (1) directly developed and brooded or released as small adults, (2) dispersed to a small degree by means of short-lived, yolk-dependent lecithotrophic larvae, or (3) dispersed great distances by longer-lived plankton-feeding planktotrophic larvae.
8) Despite the potential for dispersal, planktonic larvae often settle near their origin, owing to behavior and cyclonic currents. On the microscale, larvae use a number of cues to find their settlement site.
9) The geographic range of species with planktonic dispersal is greater than the range of species without planktonic larvae. Genetic variation can be used to identify barriers to coastal zone dispersal.
10)Migratory patterns include: Anadromy - breeding in freshwater and living in seawater (e.g., salmon, shad, sea lamprey); catadromy - Adults living in freshwater then migrate to seawater to spawn (e.g., eels); and oceanodromy- living totally in seawater but migrating from adult habitat to spawning habitat )e.g., herring and cod)
Space is a limiting resource to these colonies of colonial ascidians
When two species compete for identical, limited resources, one will be more successful and will eventually eliminate the other
two species of Paramecium
predict the outcome of
indv of species 2 on
an indv of species 1
α21 – effect of an
indv of species 1 on
an indv of species 2
α21 & α21 = competition coefficients
How does interspecific competition affect N?
How does interspecific competition affect N?
r1N1 K1-N1 - α12N2
r2N2 K2-N2- α21N1
What does it mean ifα12= 1? What ifα12= 0.5?
Estuarine salinity gradient
How do we measure competition in nature?
1. Observe the patterns of distribution and see if they conform to predictions of competition theory
One conclusion is that white and brown shrimp are in competition with each other (competition theory would predict this distribution)
Weak argument: there are multiple explanations for this distribution
Connell (1961) Experiments with barnacles
Two species – Chthamalus stellatus and Balanus balanoides(now Semibalanus balanoides)
Chthamalus adults in upper zone, juveniles in both upper and lower zone.
Balanus only in lower zone
Ha: Competition for space with Balanus prevents adult Chthalamus from occurring in the lower area
Ho: When present together Balanus has no effect on Chthalamus
expands in the absence of the
Location in intertidal zone
consumes only one prey type
consumes many prey types
CS Fig. 4.7