Population ecology focuses on the numbers and structures in populations. Part of this study involves reproduction strategies in relation to habitat.

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1 Optin G.5 - Ppulatin Eclgy G Distinguish between r-strategies and K-strategies Ppulatin eclgy fcuses n the numbers and structures in ppulatins. Part f this study invlves reprductin strategies in relatin t habitat. r- strategies Reprduce rapidly Large number f ffspring Reprduce nce Shrt lifespan Small bdies Usually pineer rganisms K- strategies Reprduce slwly Small number f ffspring Lnger lifespan Parental care Reprduce mre than nce Larger bdies Fund in stable, established habitats Because K-strategists are larger, they cnsequently require a larger habitat. Their later maturity als means that they need mre prtectin frm predatrs. They will perfrm better in envirnments where cmpetitin is high and there are n vacant niches. Examples include elephants, whales and trtise. G Discuss the envirnmental cnditins that favur either r-strategies r K-strategies. In a mre predictable envirnment, K-strategies will be used t maximise fitness, by investing resurces in lng-term develpment and lnger life. When the envirnment is unstable, it is mre beneficial t prduce a greater number f ffspring as quickly as pssible, thus emplying r-strategies. Eclgical disruptin favurs r- strategists, which include pathgens and pest species.

2 r-strategist Characteristic K-strategist ften pineer rganisms, can live in variable envirnments favured envirnment stable habitats with ther established species early in life cycle, frequently, rate f reprductin slw, with few ffspring with many ffspring shrt lifespan lng variable, but usually belw carrying capacity f the size f ppulatin small, with greater time spent rearing yung habitat pr cmpetitrs respnse t cmpetitin strng cmpetitrs frequent tendencies fr immigratin and emigratin rarer high mrtality and variable survival qualities mrtality and survival rates lw mrtality and usually regular survival qualities It is nt always pssible fr bilgists t agree n which strategies rganisms display. Fr example, if we lk at human ppulatins, the strategies seem t depend n the circumstances. In develped parts f the wrld, mst peple will cnfrm t K-strategies. In less develped parts, hwever, mre r-strategies are used. Sme rganisms display extreme r- r K- strategies, hwever mst rganisms have life histries that are n the intermediate f the cntinuum. Sme species can even switch strategies depending n the envirnmental cnditins. G Describe ne technique used t estimate the ppulatin size f an animal species based n a capture-mark-release-recapture methd In the study f ppulatins, the cllectin f accurate infrmatin n the size f ppulatins present in a habitat is very imprtant. A ttal cunt f all the members f a ppulatin is called a census. This gives the mst accurate data, hwever it is usually impractical. This is because the ppulatin may be lcated in a very large area, fast mving r nly active fr shrt perids f time.

3 A Lincln index, r the capture, mark, release, recapture (MRR) technique, is a mre practical methd fr estimating the size f a ppulatin when they are small and mbile. This can be dne with rings, tags, r dabs f paint r nail varnish. The first sample is caught and marked (n1). The methd f marking shuld be resistant t misture r the deliberate actins f the animal. It als shuld nt harm the animal, such as increased visibility t predatrs. Fr mre significant results, are larger sample shuld be caught. After their release, the marked individuals shuld be free t distribute themselves randmly amng the whle ppulatin. Once this has happened, the secnd sample is taken (n2). Any frm sample 2 that were marked (therefre belnging als t sample 1) are classified int sample 3 (n3). Once this data has been cllected, the fllwing frmula is used. A number f assumptins are made when using this technique: All individuals have an equal chance f being selected The mark des nt affect the mrtality r natality f the individuals The individuals mix randmly after release Emigratin and immigratin are balanced r zer G Describe the methds used t estimate the size f cmmercial fish stcks Since fish are an imprtant surce f fd fr many human ppulatins, they tend t be explited cmmercially, mre ften marine species. Ppulatins are cmmnly shared amng a number f harvesting cuntries. As a result, ver-fishing is becming an increasing prblem. In this case, there is cnflict between the ecnmic and cnservatin interests. The demand fr harvest and the need fr ecnmic returns fr fishermen must be balanced with ur need t sustain these resurces. In recent years, the scale f cmmercial fishing in Western Eurpe has seriusly depleted stcks.

4 If these ppulatins are cnsistently ver-fished, stcks will be rapidly depleted t pint where they cllapse and can n lnger supprt a cmmercial fishery. Fishery research services f natinal gvernments measure and assess the fur parameters in rder t gain infrmatin abut the state f fish stcks. These include: Fishing mrtality - the prprtin f fish stcks taken each year during cmmercial fishing Spawning stck bimass - the ttal mass f mature fish in the ppulatin Recruitment - the number f yung fish prduced each year which survive t enter the spawning stck Landings - the ttal annual tnnage f fish landed by the fishing fleet. Obtaining the Infrmatin Market Sampling Infrmatin abut fish length and age is cllected frm landing samples The age structure f the ppulatin is estimated Changes in availability can be identified Discard Sampling Mass f fish caught then discarded is measured The discarded fish are either f n cmmercial value, belw legal size, r quta limits have been reached A mre accurate picture f the available stcks can be created Research Vessel Surveys The distributin and abundance f adult stcks is investigated Using snar, the bimass f surface species can be detected Trawling surveys give an index f the abundance f bttm-dwelling species Eclgical cmputer mdels are used with this data t create a picture f the ttal bimass f living fish acrss the area studied, and als track changes in trends

5 G Outline the cncept f maximum sustainable yield in the cnservatin f fish stcks The maximum sustainable yield (r MSY) f a stck represents the maximum average catch that a stck can sustain ver an indefinite perid f time. This will crrespnd t the ptimum balance between the reprductive rate and the grwth rate f the stck, as well as the death due t harvesting and natural mrtality. The MSY shuld be exactly half the carrying capacity f the species, since it is at this stage that the ppulatin grwth is the highest. Harvesting at MSY will usually result in lwer harvest rate at many fisheries. The maximum sustainable yield is usually higher than the ptimum sustainable yield. Fr the MSY t be calculated, a gd knwledge Natural Mrtality f the relatinship between the size f the stck and the number f juveniles prduced each year is required. Hwever, there is a natural variatin Harvesting Optimum Balance Reprductin in the prductin f juveniles, which makes establishing this relatinship difficult. This may lead t setting the maximum sustainable yield t high r lw. Data needs t be cllected ver at Grwth least 20 years. There are still reliable methds fr btaining an adequate apprximatin f the MSY

6 G Discuss internatinal measures that wuld prmte the cnservatin f fish Fishing natins have had t implement varius cntrl measure t cpe with their verexpliting f their fishing resurces. These have included bans n the fishing f certain species. If these are respected, breeding stcks are allwed t recver. The Eurpean Unin is regulating fishing arund the shres f the member states thrugh varius measures: Technical Cnservatin (TC) Ttal Allwable Catches (TAC) and Qutas This maintains breeding stcks, preventing yung fish frm being remved frm the ppulatin It invlves setting minimum landing sizes and specific mesh sizes s that small fish may escape An annual mass f fish that may be landed is agreed The mass is based n advice f scientists frm the Internatinal Cuncil fr Explitatin f the Sea (ICES) Separatr devices can be used t avid vulnerable stck Types f fishing gear may be restricted Each state then receives a quta accrding t their dependence n fishing Certain areas may be clsed dwn frm fishing At the same time, funding is maintained fr natinal marine bilgy statin t carry ut research t gain a clear picture f the eclgy in that area, and f the key stages f the life cycles rganisms in the relevant fd chain. Other measures are: Mnitring f stcks and reprductin rates Qutas fr catches Minimum net sizes t stp immature fish being caught Banning drift nets, which catch many different species indiscriminately Mratria (temprary suspensin) n catching endangered species